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<article id="spring-cloud与dubbo的区别详解" class="article article-type-spring" itemscope itemprop="blogPost">
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<a href="/2019/09/18/cloud与dubbo的区别详解/" class="article-date">
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<a class="article-title" href="/2019/09/18/cloud与dubbo的区别详解/">Springcloud与dubbo的区别详解</a>
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<p>面试问到的关于spring cloud理解和spring cloud与dubbo的区别详解<br>今天下午面试被问到这个问题,当时没答上来,毕竟之前工作也都只是简单的使用,并没有真正去了解过两个之间的区别<br>晚上自己查了一些文档,有点感悟在这里写一下<br>首先两个都是国内比较火的微服务架构<br>先介绍一下微服务<br><strong>微服务架构是一种架构模式，它将单一应用程序划分成一组小的服务，服务之间互相配合，达到最终的目的</strong></p>
<p>优点是可以将繁杂的代码堆分解,每一个微服务实现单一的功能,并通过接口与其他服务沟通合作<br>每个微服务之间相互独立部署技术使用更加灵活<br>这里先介绍一下我比较熟悉的spring cloud ,它基于Spring Boot实现各种功能</p>
<h3 id="核心为以下五个"><a href="#核心为以下五个" class="headerlink" title="核心为以下五个"></a>核心为以下五个</h3><h4 id="1-Eureka-注册中心——Netflix-Eureka-功能类似于dubbo的注册中心，比如zookeeper。"><a href="#1-Eureka-注册中心——Netflix-Eureka-功能类似于dubbo的注册中心，比如zookeeper。" class="headerlink" title="1.Eureka 注册中心——Netflix Eureka 功能类似于dubbo的注册中心，比如zookeeper。"></a>1.Eureka 注册中心——Netflix Eureka 功能类似于dubbo的注册中心，比如zookeeper。</h4><p>eureka是一个基于REST的服务，用于定位服务，以实现云端中间层服务发现和故障转移。服务注册与发现对于微服务架构来说是非常重要的，有了服务发现和注册，只需要使用服务的标识符，就可以访问到服务，而不需要修改服务<br>Eureka server提供服务注册和发现.<br> Eureka Server提供服务注册服务。各个服务提供者节点启动后，会在Eureka Server中进行注册，这样Eureka server中的服务存储可用信息并且可以直观的看到.<br>Service Provider服务提供方将自身服务注册到Eureka，从而使服务消费方能够找到。<br>Service Consumer服务消费方从Eureka获取注册服务列表，从而能够消费服务。</p>
<h4 id="2-客服端负载均衡——Netflix-Ribbon-Feign"><a href="#2-客服端负载均衡——Netflix-Ribbon-Feign" class="headerlink" title="2.客服端负载均衡——Netflix Ribbon/Feign"></a>2.客服端负载均衡——Netflix Ribbon/Feign</h4><p>为了提供并发量，有时同一个服务提供者可以部署多个。这个客户端在调用时要根据一定的负责均衡策略完成负载调用。<br>Ribbon是Netflix发布的云中间层服务开源项目，主要功能是提供客户端负载均衡算法。Ribbon客户端组件提供一系列完善的配置项，如，连接超时，重试等。<br> 比如今天面试就问到了连接超时时间<br> 负载均衡算法最常用的有随机RandomRule和轮询RoundRobinRule两种<br> 代码网上有很多就不一一列出<br> Feign是一个声明式的Web Service客户端，它的目的就是让Web Service调用更加简单,相当于在Ribbon的基础上继续封装了一层,类似于springmvc在servlet的基础上做了一层封装<br> 它 提供了HTTP请求的模板，通过编写简单的接口和插入注解，就可以定义好HTTP请求的参数、格式、地址等信息。会完全代理HTTP请求，<br> 可插拔的注解支持，包括Feign注解和JAX-RS注解;<br>支持可插拔的HTTP编码器和解码器;<br>支持Hystrix和它的Fallback;<br>支持Ribbon的负载均衡;<br>支持HTTP请求和响应的压缩。<br>这看起来有点像我们springmvc模式的Controller层的RequestMapping映射 Feign是用@FeignClient来映射服务的。</p>
<h4 id="3-服务网关——Netflix-Zuul"><a href="#3-服务网关——Netflix-Zuul" class="headerlink" title="3.服务网关——Netflix Zuul"></a>3.服务网关——Netflix Zuul</h4><p>Zuul 是netflix开源的一个API Gateway 服务器, 本质上是一个web servlet应用。<br>Zuul 在云平台上提供动态路由，监控，弹性，安全等边缘服务的框架。Zuul 相当于是设备和 Netflix 流应用的 Web 网站后端所有请求的前门，也要注册入Eureka.<br>前面这一层俗称为“网关层”，其存在意义在于，将”1对N”问题 转换成了”1对1”问题（路由），同时在请求到达真正的微服务之前，可以做一些预处理（过滤），比如：来源合法性检测，权限校验，反爬虫之类…</p>
<h4 id="4-断路器——Netflix-Hystrix"><a href="#4-断路器——Netflix-Hystrix" class="headerlink" title="4.断路器——Netflix Hystrix"></a>4.断路器——Netflix Hystrix</h4><p>在理想状态下，一个应用依赖的服务都是健康可用的，我们可以正常的处理所有的请求,但是天有不测风云<br> 当微服务中某一个服务出问题的时候发生延迟，所有的请求都阻塞在依赖的服务,大多数服务器的线程池就出现阻塞(BLOCK),影响整个线上服务的稳定性<br>高并发的依赖失败时如果没有隔离措施，当前应用服务就有被拖垮的风险<br> Hystrix是保证微服务群健壮框架,做了隔离,熔断,降级等操作.最终达到不会由于某一个服务出问题而导致雪崩现象,让整体群死掉.</p>
<h5 id="资源隔离（限流）："><a href="#资源隔离（限流）：" class="headerlink" title="资源隔离（限流）："></a>资源隔离（限流）：</h5><p> 包括线程池隔离和信号量隔离，限制调用分布式服务的资源使用，某一个调用的服务出现问题不会影响其他服务调用。<br>(1) 线程池隔离模式：使用一个线程池来存储当前请求，线程池对请求作处理，设置任务返回处理超时时间，堆积的请求先入线程池队列。这种方式要为每个依赖服务申请线程池，有一定的资源消耗，好处是可以应对突发流量（大量流量来临时，处理不完可将数据存储到线程池队里慢慢处理）<br>(2）信号量隔离模式：使用一个原子计数器（或信号量）记录当前有多少个线程在运行，请求来先判断计数器的数值，若超过设置的最大线程个数则丢弃该类型的新请求，若不超过则执行计数操作请求来计数器+1，请求返回计数器-1。这种方式是严格的控制线程且立即返回模式，无法应对突发流量（流量洪峰来临时，处理的线程超过数量，其他的请求会直接返回，不继续去请求依赖的服务）</p>
<h5 id="融断："><a href="#融断：" class="headerlink" title="融断："></a>融断：</h5><p> 当失败率达到阀值自动触发降级(如因网络故障/超时造成的失败率高)，熔断器触发的快速失败会进行快速恢复。<br> 正常情况下，断路器处于关闭状态(Closed)，<br>如果调用持续出错或者超时，电路被打开进入熔断状态(Open)，后续一段时间内的所有调用都会被拒绝(Fail Fast)，<br>一段时间以后，保护器会尝试进入半熔断状态(Half-Open)，允许少量请求进来尝试，<br> 如果调用仍然失败，则回到熔断状态<br> 如果调用成功，则回到电路闭合状态;</p>
<h5 id="降级机制："><a href="#降级机制：" class="headerlink" title="降级机制："></a>降级机制：</h5><p> 超时降级、资源不足时(线程或信号量)降级，降级后可以配合降级接口返回托底数据。<br> 所谓降级，就是当某个服务熔断之后，服务器将不再被调用，此时客户端可以自己准备一个本地的fallback回调，返回一个缺省值。<br>这样做，虽然服务水平下降，但好歹可用，比直接挂掉要强，当然这也要看适合的业务场景。</p>
<h5 id="缓存："><a href="#缓存：" class="headerlink" title="缓存："></a>缓存：</h5><p> 提供了请求缓存、请求合并实现。</p>
<h4 id="5-分布式配置——Spring-Cloud-Config"><a href="#5-分布式配置——Spring-Cloud-Config" class="headerlink" title="5.分布式配置——Spring Cloud Config"></a>5.分布式配置——Spring Cloud Config</h4><p> 微服务架构中，每个项目都有一个yml配置，管理起来麻烦。spring cloud config主要用来管理这些yml<br> 它支持配置服务放在配置服务的内存中（即本地），也支持放在远程Git仓库中。在spring cloud config 组件中，分两个角色，一是config server，二是config client。<br>今天由于时间有限先介绍下概念,改天再具体将代码实现</p>
<h3 id="接下来说说两者区别"><a href="#接下来说说两者区别" class="headerlink" title="接下来说说两者区别"></a>接下来说说两者区别</h3><p>Dubbo，是阿里巴巴服务化治理的核心框架，在中国被广泛使用；<br>Spring Cloud 是Spring的产品,他们专注开发出通用、开源、稳健的开源框架</p>
<pre><code>对比了网上一些说法总的来说</code></pre><p>社区活跃度spring更加活跃<br>Dubbo有中文文档对中国开发者来说更加友好<br>Dubbo只是实现了服务治理，而Spring Cloud分别覆盖了微服务架构下的方方面面，服务治理只是其中的一个方面，一定程度来说，Dubbo只是Spring Cloud Netflix中的一个子集。但是在选择框架上，方案完整度恰恰是一个需要重点关注的内容。<br>Dubbo晋升为Apache顶级项目对Dubbo将进一步的优化,潜力无限<br> 并且两者之上还有一个进化版本<br> spring-cloud-dubbo</p>
<p> <a href="http://springcloud.cn/view/327" target="_blank" rel="noopener">详情见Spring Cloud中国社区</a></p>
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<article id="photo-mybatis" class="article article-type-photo" itemscope itemprop="blogPost">
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<time datetime="2019-05-10T15:17:32.000Z" itemprop="datePublished">2019-05-10</time>
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<a class="article-title" href="/2019/05/10/mybatis/">mybatis中的$与#</a>
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<p>#{}(接收普通参数,预编译,性能好,安全性高)<br>$正好相反他是直接拼接字符串</p>
<ol>
<li>${}</li>
</ol>
<ul>
<li>只能获取的是传过来的对象的一个属性(拼接字符串)<pre><code>select * from product where id= ${id}
-> 危险:有SQL注入的问题
这种方式能不用就不要使用</code></pre></li>
</ul>
<p> 2.#{}</p>
<ul>
<li>#：即可以获取传过来的一个值，也可以获取传过来的对象的属性(占位)<pre><code>select * from product where id= ?
防SQL注入,性能也更好</code></pre></li>
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<time datetime="2018-06-28T15:19:33.000Z" itemprop="datePublished">2018-06-28</time>
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<a class="article-title" href="/2018/06/28/mybatisTwo/">mybatis 的十分详细的入门教程第二弹</a>
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<p><strong>mybatis 的十分详细的入门教程第二弹</strong></p>
<h2 id="步骤-复习"><a href="#步骤-复习" class="headerlink" title="步骤(复习)"></a>步骤(复习)</h2><h3 id="导包"><a href="#导包" class="headerlink" title="导包"></a>导包</h3><p> 核心包</p>
<p>mybatis-3.2.1.jar</p>
<p> 依赖包</p>
<p>asm-3.3.1.jar<br>cglib-2.2.2.jar<br>commons-logging-1.1.1.jar<br>javassist-3.17.1-GA.jar<br>log4j-1.2.17.jar<br>slf4j-api-1.7.2.jar<br>slf4j-log4j12-1.7.2.jar</p>
<p> 数据库依赖包</p>
<p>mysql-connector-java-5.1.26-bin.jar</p>
<h3 id="domain"><a href="#domain" class="headerlink" title="domain"></a>domain</h3><p>数据库建表</p>
<p>domain映射</p>
<p>getset</p>
<p>tostring</p>
<h3 id="配置文件"><a href="#配置文件" class="headerlink" title="配置文件"></a>配置文件</h3><p>拷贝文档</p>
<p>修改为自己的数据库配置</p>
<p>引用数据库四大金刚properties文件</p>
<h3 id="dao"><a href="#dao" class="headerlink" title="dao"></a>dao</h3><p>新建接口</p>
<p>mapper.xml拷贝文档</p>
<p>写入sql查询或其他操作</p>
<p>mybatis配置文件引入mapper.xml</p>
<h3 id="log4j"><a href="#log4j" class="headerlink" title="log4j"></a>log4j</h3><p>拷贝log4j.properties文件</p>
<h3 id="测试"><a href="#测试" class="headerlink" title="测试"></a>测试</h3><h2 id="映射"><a href="#映射" class="headerlink" title="映射"></a>映射</h2><p>(mapper==dao==repostory)</p>
<h3 id="mapper层"><a href="#mapper层" class="headerlink" title="mapper层"></a>mapper层</h3><p>不需要实现类</p>
<p>mapper.xml文件放入mapper包</p>
<p>名字跟接口一致==类名+”mapper”</p>
<p>命名空间 === mapper接口全限定名</p>
<p>方法名 === sql 的 Id</p>
<p>引入mapper.xml</p>
<p>session.getMapper()</p>
<p>自动获取实现类</p>
<h3 id="sql写到类里"><a href="#sql写到类里" class="headerlink" title="sql写到类里"></a>sql写到类里</h3><p>接口查询方法头加注解@select(sql)</p>
<p>其他操作注解与sql一致</p>
<h3 id="高级-模糊查询"><a href="#高级-模糊查询" class="headerlink" title="高级||模糊查询"></a>高级||模糊查询</h3><p>写一个query类写入查询条件</p>
<p>sql传入query对象</p>
<p>sql里拼接字符串的放方法 concat(可变参数,列名随意放,可变参数)</p>
<p>damo</p>
<p><img src="https://img-blog.csdnimg.cn/20190803221210161.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2pjZXRwb29y,size_16,color_FFFFFF,t_70" alt="在这里插入图片描述"></p>
<p>mybatis可以进行if判断</p>
<p>demo</p>
<p><img src="https://img-blog.csdnimg.cn/20190803221310928.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2pjZXRwb29y,size_16,color_FFFFFF,t_70" alt="在这里插入图片描述"></p>
<h4 id="特殊符号"><a href="#特殊符号" class="headerlink" title="特殊符号"></a>特殊符号</h4><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">&lt; <span class="tag"><</span></span><br><span class="line"><span class="tag">&<span class="attr">gt</span>; ></span></span><br><span class="line"><![CDATA[数据]]> cdata中的数据不会被识别为语法</span><br></pre></td></tr></table></figure>
<h4 id="where查询问题"><a href="#where查询问题" class="headerlink" title="where查询问题"></a>where查询问题</h4><p>demo</p>
<p>[外链图片转存失败(img-QEkuVrdp-1564823219925)(1564712967398.png)]<img src="https://img-blog.csdnimg.cn/20190803221439485.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2pjZXRwb29y,size_16,color_FFFFFF,t_70" alt="在这里插入图片描述"></p>
<h4 id="批处理"><a href="#批处理" class="headerlink" title="批处理"></a>批处理</h4><h5 id="批添加"><a href="#批添加" class="headerlink" title="批添加"></a>批添加</h5><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--这里写集合 批量添加--></span></span><br><span class="line"> <span class="tag"><<span class="name">insert</span> <span class="attr">id</span>=<span class="string">"bitchSave"</span> <span class="attr">parameterType</span>=<span class="string">"list"</span>></span></span><br><span class="line"> insert into employee (name, age, sex) values </span><br><span class="line"> <span class="tag"><<span class="name">foreach</span> <span class="attr">collection</span>=<span class="string">"list"</span> <span class="attr">item</span>=<span class="string">"emp"</span> <span class="attr">separator</span>=<span class="string">","</span>></span></span><br><span class="line"> ( #{emp.name},#{emp.age},#{emp.sex})</span><br><span class="line"> <span class="tag"></<span class="name">foreach</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">insert</span>></span></span><br></pre></td></tr></table></figure>
<h5 id="两种批删除"><a href="#两种批删除" class="headerlink" title="两种批删除"></a>两种批删除</h5><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--批删除list--></span></span><br><span class="line"> <span class="tag"><<span class="name">delete</span> <span class="attr">id</span>=<span class="string">"bitchDelete"</span> <span class="attr">parameterType</span>=<span class="string">"list"</span>></span></span><br><span class="line"> delete from employee where id in</span><br><span class="line"> <span class="tag"><<span class="name">foreach</span> <span class="attr">collection</span>=<span class="string">"list"</span> <span class="attr">item</span>=<span class="string">"id"</span> <span class="attr">separator</span>=<span class="string">","</span> <span class="attr">open</span>=<span class="string">"("</span> <span class="attr">close</span>=<span class="string">")"</span>></span></span><br><span class="line"> #{id}</span><br><span class="line"> <span class="tag"></<span class="name">foreach</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">delete</span>></span></span><br><span class="line"> <span class="comment"><!--批删除arr--></span></span><br><span class="line"> <span class="tag"><<span class="name">delete</span> <span class="attr">id</span>=<span class="string">"bitchDeleteByArr"</span> <span class="attr">parameterType</span>=<span class="string">"long[]"</span>></span></span><br><span class="line"> delete from employee where id in</span><br><span class="line"> <span class="tag"><<span class="name">foreach</span> <span class="attr">collection</span>=<span class="string">"array"</span> <span class="attr">item</span>=<span class="string">"id"</span> <span class="attr">separator</span>=<span class="string">","</span> <span class="attr">open</span>=<span class="string">"("</span> <span class="attr">close</span>=<span class="string">")"</span>></span></span><br><span class="line"> #{id}</span><br><span class="line"> <span class="tag"></<span class="name">foreach</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">delete</span>></span></span><br></pre></td></tr></table></figure>
<h5 id="动态修改"><a href="#动态修改" class="headerlink" title="动态修改"></a>动态修改</h5><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--动态修改,<set>可以自动加set关键字去逗号--></span></span><br><span class="line"> <span class="tag"><<span class="name">update</span> <span class="attr">id</span>=<span class="string">"dynamicUpdate"</span> <span class="attr">parameterType</span>=<span class="string">"cn.itsource.domain.Employee"</span> ></span></span><br><span class="line"> update employee</span><br><span class="line"> <span class="tag"><<span class="name">set</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">if</span> <span class="attr">test</span>=<span class="string">"name!=null and name!=''"</span>></span></span><br><span class="line"> name = #{name},</span><br><span class="line"> <span class="tag"></<span class="name">if</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">if</span> <span class="attr">test</span>=<span class="string">"age!=null"</span>></span></span><br><span class="line"> age = #{age},</span><br><span class="line"> <span class="tag"></<span class="name">if</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">if</span> <span class="attr">test</span>=<span class="string">"sex!=null"</span>></span></span><br><span class="line"> sex = #{sex},</span><br><span class="line"> <span class="tag"></<span class="name">if</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">set</span>></span></span><br><span class="line"> where id = #{id}</span><br><span class="line"> <span class="tag"></<span class="name">update</span>></span></span><br></pre></td></tr></table></figure>
<h2 id="映射关系"><a href="#映射关系" class="headerlink" title="映射关系"></a>映射关系</h2><h3 id="多对一-many-to-One"><a href="#多对一-many-to-One" class="headerlink" title="多对一(many to One)"></a>多对一(many to One)</h3><p>== 一对一</p>
<p>新建两个表</p>
<p>多方添加一方的外键</p>
<p>创建😀domain</p>
<p>多方持有一方对象</p>
<p>创建mapper</p>
<p>创建mapper.xml</p>
<p>核心配置文件引入mapper.xml</p>
<h4 id="写保存方法"><a href="#写保存方法" class="headerlink" title="写保存方法"></a>写保存方法</h4><p>多方sql里#{dir.id}点出一方id</p>
<p>多方中保存一方</p>
<p>先保存一方,再保存多方</p>
<p>一方保存后获取id才能添加外键</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--添加多方方法,使用#{dir.id}类中的分类点出id存入数据库--></span></span><br><span class="line"> <span class="tag"><<span class="name">insert</span> <span class="attr">id</span>=<span class="string">"save"</span> <span class="attr">parameterType</span>=<span class="string">"cn.itsource._02many2one.Product"</span>></span></span><br><span class="line"> insert into t_product (name, dir_id)</span><br><span class="line"> values (#{name}, #{dir.id})</span><br><span class="line"> <span class="tag"></<span class="name">insert</span>></span></span><br></pre></td></tr></table></figure>
<h4 id="查询所有"><a href="#查询所有" class="headerlink" title="查询所有"></a>查询所有</h4><p>方法与mapper.xml对应</p>
<p>join on</p>
<p>以下三种方式都使用这条sql</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">select</span> p.id pid, p.name pname, dir.id dirid, dir.name dirname</span><br><span class="line"><span class="keyword">from</span> T_product p</span><br><span class="line"><span class="keyword">join</span> productdir dir <span class="keyword">on</span> dir.id = p.dir_id</span><br></pre></td></tr></table></figure>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--查询所有的sql 引入下面三条ProductResultmap返回--></span></span><br><span class="line"> <span class="tag"><<span class="name">select</span> <span class="attr">id</span>=<span class="string">"findAll"</span> <span class="attr">resultMap</span>=<span class="string">"ProductResultmap"</span>></span></span><br><span class="line"> select p.id pid, p.name pname, dir.id dirid, dir.name dirname</span><br><span class="line"> from T_product p</span><br><span class="line"> join productdir dir on dir.id = p.dir_id</span><br><span class="line"> <span class="tag"></<span class="name">select</span>></span></span><br></pre></td></tr></table></figure>
<p>三种方法从多方查询出一方</p>
<p>第一种官方推荐</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--查询所有的resultMap 官方推荐的写法--></span></span><br><span class="line"> <span class="comment"><!--id为标识符 type是多方类型--></span></span><br><span class="line"> <span class="tag"><<span class="name">resultMap</span> <span class="attr">id</span>=<span class="string">"ProductResultmap"</span> <span class="attr">type</span>=<span class="string">"cn.itsource._02many2one.Product"</span>></span></span><br><span class="line"> <span class="comment"><!--分别是属性和列中的名字 id使用<id> 其他属性使用<result>--></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">property</span>=<span class="string">"id"</span> <span class="attr">column</span>=<span class="string">"pid"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">column</span>=<span class="string">"pname"</span> <span class="attr">property</span>=<span class="string">"name"</span>/></span></span><br><span class="line"></span><br><span class="line"> <span class="comment"><!--关联 association javaType一方的类型 property 一方在多方类里的属性名--></span></span><br><span class="line"> <span class="tag"><<span class="name">association</span> <span class="attr">property</span>=<span class="string">"dir"</span> <span class="attr">javaType</span>=<span class="string">"cn.itsource._02many2one.ProductDir"</span>></span></span><br><span class="line"> <span class="comment"><!--分别是属性和列中的名字 id使用<id> 其他属性使用<result>--></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">property</span>=<span class="string">"id"</span> <span class="attr">column</span>=<span class="string">"dirid"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">property</span>=<span class="string">"name"</span> <span class="attr">column</span>=<span class="string">"dirname"</span>/></span></span><br><span class="line"> <span class="tag"></<span class="name">association</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">resultMap</span>></span></span><br></pre></td></tr></table></figure>
<p>第二种野路子省事</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--查询所有的resultMap 省事的野路子--></span></span><br><span class="line"> <span class="tag"><<span class="name">resultMap</span> <span class="attr">id</span>=<span class="string">"ProductResultmap2"</span> <span class="attr">type</span>=<span class="string">"cn.itsource._02many2one.Product"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">column</span>=<span class="string">"dirid"</span> <span class="attr">property</span>=<span class="string">"dir.id"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">column</span>=<span class="string">"dirname"</span> <span class="attr">property</span>=<span class="string">"dir.name"</span>/></span></span><br><span class="line"> <span class="tag"></<span class="name">resultMap</span>></span></span><br></pre></td></tr></table></figure>
<p>第三种性能最差发送多条sql能不用则不用</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!--查询所有的resultMap 嵌套映射 --></span></span><br><span class="line"> <span class="tag"><<span class="name">resultMap</span> <span class="attr">id</span>=<span class="string">"ProductResultmap3"</span> <span class="attr">type</span>=<span class="string">"cn.itsource._02many2one.Product"</span>></span></span><br><span class="line"> <span class="comment"><!--分别是属性和列中的名字 id使用<id> 其他属性使用<result>--></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">property</span>=<span class="string">"id"</span> <span class="attr">column</span>=<span class="string">"pid"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">column</span>=<span class="string">"pname"</span> <span class="attr">property</span>=<span class="string">"name"</span>/></span></span><br><span class="line"></span><br><span class="line"> <span class="comment"><!--性能较差,能不用就不要用 select="cn.itsource._02many2one.ProductDirMapper.findOne"是另一条sql column="dirid"是传递过去的参数--></span></span><br><span class="line"> <span class="tag"><<span class="name">association</span> <span class="attr">property</span>=<span class="string">"dir"</span> <span class="attr">javaType</span>=<span class="string">"cn.itsource._02many2one.ProductDir"</span></span></span><br><span class="line"><span class="tag"> <span class="attr">column</span>=<span class="string">"dirid"</span> <span class="attr">select</span>=<span class="string">"cn.itsource._02many2one.ProductDirMapper.findOne"</span>/></span></span><br><span class="line"> <span class="tag"></<span class="name">resultMap</span>></span></span><br></pre></td></tr></table></figure>
<h3 id="一对多"><a href="#一对多" class="headerlink" title="一对多"></a>一对多</h3><p>== 多对多</p>
<p>关联集合使用collection而不是association</p>
<p>官方推荐方法 一条sql性能比较好 返回</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"> <span class="comment"><!--第一种方法--></span></span><br><span class="line"> <span class="tag"><<span class="name">select</span> <span class="attr">id</span>=<span class="string">"findAll"</span> <span class="attr">resultMap</span>=<span class="string">"findAllresultMap2"</span>></span></span><br><span class="line"> select p.id pid, p.name pname, dir.id dirid, dir.name dirname</span><br><span class="line"> from productdir dir</span><br><span class="line"> join t_product p on p.dir_id = dir.id</span><br><span class="line"> <span class="tag"></<span class="name">select</span>></span></span><br><span class="line"> </span><br><span class="line"> </span><br><span class="line"> </span><br><span class="line"><span class="comment"><!--返回格式map--></span></span><br><span class="line"> <span class="comment"><!--第一种方法的resultMap--></span></span><br><span class="line"> <span class="tag"><<span class="name">resultMap</span> <span class="attr">id</span>=<span class="string">"findAllresultMap"</span> <span class="attr">type</span>=<span class="string">"cn.itsource._03one2many.ProductDir"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">property</span>=<span class="string">"id"</span> <span class="attr">column</span>=<span class="string">"dirid"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">property</span>=<span class="string">"name"</span> <span class="attr">column</span>=<span class="string">"dirname"</span>/></span></span><br><span class="line"></span><br><span class="line"> <span class="comment"><!--property="products"是一方里的多方属性--></span></span><br><span class="line"> <span class="comment"><!--ofType="cn.itsource._03one2many.Product"是多方属性--></span></span><br><span class="line"> <span class="comment"><!--一对多里使用conlection标签--></span></span><br><span class="line"> <span class="tag"><<span class="name">collection</span> <span class="attr">property</span>=<span class="string">"products"</span> <span class="attr">ofType</span>=<span class="string">"cn.itsource._03one2many.Product"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">column</span>=<span class="string">"pid"</span> <span class="attr">property</span>=<span class="string">"id"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">column</span>=<span class="string">"pname"</span> <span class="attr">property</span>=<span class="string">"name"</span>/></span></span><br><span class="line"> <span class="tag"></<span class="name">collection</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">resultMap</span>></span></span><br></pre></td></tr></table></figure>
<p>第二种方式性能差</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"> <span class="comment"><!--第二种方法,先查一方,再用多方查询一方发送多条sql--></span></span><br><span class="line"> <span class="tag"><<span class="name">select</span> <span class="attr">id</span>=<span class="string">"findAll"</span> <span class="attr">resultMap</span>=<span class="string">"findAllresultMap2"</span>></span></span><br><span class="line"> select dir.id dirid, dir.name dirname</span><br><span class="line"> from productdir dir</span><br><span class="line"> <span class="tag"></<span class="name">select</span>></span></span><br><span class="line"><span class="comment"><!--返回格式map--></span></span><br><span class="line"> <span class="comment"><!--惯例还有第二种方法 性能最差发送多条sql能不用则不用 column="dirid"是传递过去的参数</span></span><br><span class="line"><span class="comment"> select="cn.itsource._03one2many.ProductMapper.findAllBydirId"是sql的路径</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">--></span></span><br><span class="line"> <span class="tag"><<span class="name">resultMap</span> <span class="attr">id</span>=<span class="string">"findAllresultMap2"</span> <span class="attr">type</span>=<span class="string">"cn.itsource._03one2many.ProductDir"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">property</span>=<span class="string">"id"</span> <span class="attr">column</span>=<span class="string">"dirid"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">property</span>=<span class="string">"name"</span> <span class="attr">column</span>=<span class="string">"dirname"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">collection</span> <span class="attr">property</span>=<span class="string">"products"</span> <span class="attr">ofType</span>=<span class="string">"cn.itsource._03one2many.Product"</span> <span class="attr">select</span>=<span class="string">"cn.itsource._03one2many.ProductMapper.findAllBydirId"</span> <span class="attr">column</span>=<span class="string">"dirid"</span> ></span></span><br><span class="line"> <span class="tag"><<span class="name">id</span> <span class="attr">column</span>=<span class="string">"pid"</span> <span class="attr">property</span>=<span class="string">"id"</span>/></span></span><br><span class="line"> <span class="tag"><<span class="name">result</span> <span class="attr">column</span>=<span class="string">"pname"</span> <span class="attr">property</span>=<span class="string">"name"</span>></span><span class="tag"></<span class="name">result</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">collection</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">resultMap</span>></span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment"><!--调用的sql 用一方id查询多方--></span></span><br><span class="line"></span><br><span class="line"> <span class="tag"><<span class="name">select</span> <span class="attr">id</span>=<span class="string">"findAllBydirId"</span> <span class="attr">parameterType</span>=<span class="string">"Long"</span> <span class="attr">resultType</span>=<span class="string">"cn.itsource._03one2many.Product"</span>></span></span><br><span class="line"> select * from t_product where dir_id = #{dirid}</span><br><span class="line"> <span class="tag"></<span class="name">select</span>></span></span><br></pre></td></tr></table></figure>
<h3 id="缓存"><a href="#缓存" class="headerlink" title="缓存"></a>缓存</h3><h4 id="自带一级缓存"><a href="#自带一级缓存" class="headerlink" title="自带一级缓存"></a>自带一级缓存</h4><h4 id="二级缓存"><a href="#二级缓存" class="headerlink" title="二级缓存"></a>二级缓存</h4><p>核心配置中加入<cache>标签即可</cache></p>
<p>然后domain必须序列化</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">实现Serializable</span><br></pre></td></tr></table></figure>
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<a class="article-title" href="/2018/06/19/mybatisOne/">mybatis 的十分详细的入门教程</a>
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<h2 id="一-mybatis-的十分详细的入门教程"><a href="#一-mybatis-的十分详细的入门教程" class="headerlink" title="一. mybatis 的十分详细的入门教程"></a>一. mybatis 的十分详细的入门教程</h2><h3 id="mybatis起源"><a href="#mybatis起源" class="headerlink" title="mybatis起源?"></a>mybatis起源?</h3><p>MyBatis 本是apache的一个开源项目iBatis,<br>2010年这个项目由apache software foundation 迁移到了google code，<br>并且改名为MyBatis<br>iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。<br>iBATIS提供的持久层框架包括SQL Maps（XML映射配置）和Data Access Objects（Dao）</p>
<h3 id="mybati介绍"><a href="#mybati介绍" class="headerlink" title="mybati介绍"></a>mybati介绍</h3><p>MyBatis 是一个支持普通SQL查询，存储过程( Oracle最后一天)和高级映射的优秀持久层框架。<br>MyBatis 消除了几乎所有的JDBC代码和手工设置参数以及结果集的检索。<br>MyBatis 使用简单的 XML或注解用于配置和原始映射，将接口和 Java 的POJOs（Plain Old Java Objects，普通的 Java对象）映射成数据库中的记录。<br>MyBatis不能自动创建表，如果能够自动建表，必须自己先准备好建表的sql语句。</p>
<h3 id="起步"><a href="#起步" class="headerlink" title="起步"></a>起步</h3><p> 步骤<br>1 导包<br>2 建表(product)<br>3 domain(Product)<br>4 准备dao层(CRUD)<br>5 测试(不是必需的)<br>注意:我们要引哪些包?<br>1 一定要引入驱动包(不要忘了)<br>2 导入mybatis的核心包<br>3 导入mybatis的依赖包</p>
<p>jar包可以去网上下载<br><img src="https://img-blog.csdnimg.cn/20190801210153975.png" alt="导入jar包"></p>
<p>MyBatis-Config.xml配置文件(直接拷贝,后续会讲解)</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br></pre></td><td class="code"><pre><span class="line"><?xml version="1.0" encoding="UTF-8" ?></span><br><span class="line"><!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"</span><br><span class="line"> "http://mybatis.org/dtd/mybatis-3-config.dtd"> </span><br><span class="line"></span><br><span class="line"><configuration></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> <!--引入配置文件四大金刚--></span><br><span class="line"> <properties resource="db.properties"></properties></span><br><span class="line"></span><br><span class="line"> <!--别名--></span><br><span class="line"> <typeAliases></span><br><span class="line"> <package name="cn.itsource.domain"></package></span><br><span class="line"> </typeAliases></span><br><span class="line"></span><br><span class="line"> <!--环境们--><!--默认环境--></span><br><span class="line"> <environments default="development"></span><br><span class="line"> <!--环境--></span><br><span class="line"> <environment id="development"></span><br><span class="line"></span><br><span class="line"> <transactionManager type="JDBC"></transactionManager></span><br><span class="line"> <!--</span><br><span class="line"> dataSource:数据库，连接池(配置四大金刚:driven,url,username,password)</span><br><span class="line"> type:连接池的类型 UNPOOLED|POOLED|JNDI</span><br><span class="line"> UNPOOLED: 这个数据源的实现是每次被请求时简单打开和关闭连接</span><br><span class="line"> POOLED:这是 JDBC 连接对象的数据源连接池的实现</span><br><span class="line"> JNDI:这个数据源的实现是为了使用如 Spring 或应用服务器这类的容器</span><br><span class="line"> --></span><br><span class="line"> <dataSource type="POOLED"></span><br><span class="line"> <property name="driver" value="${jdbc.driver}"></property></span><br><span class="line"> <property name="url" value="${jdbc.url}"></property></span><br><span class="line"> <property name="username" value="${jdbc.username}"></property></span><br><span class="line"> <property name="password" value="${jdbc.password}"></property></span><br><span class="line"></span><br><span class="line"> </dataSource></span><br><span class="line"> </environment></span><br><span class="line"> </environments></span><br><span class="line"><mappers></span><br><span class="line"> <!--在核心配置文件中找到咱们的SQL映射文件--></span><br><span class="line"> <mapper resource="cn/itsource/dao/Productmaper.xml"></mapper></span><br><span class="line"></mappers></span><br><span class="line"></configuration></span><br></pre></td></tr></table></figure>
<p>properties文件</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">jdbc.driver=com.mysql.jdbc.Driver #数据库驱动</span><br><span class="line">jdbc.url=jdbc:mysql:///mybatis #mybatis改为你的表名</span><br><span class="line">jdbc.username=root #数据库账号</span><br><span class="line">jdbc.password=123456 #数据库密码</span><br><span class="line">#四大金刚</span><br></pre></td></tr></table></figure>
<p>核心文件中有一个mappers,它指向了一个映射文件。映射文件在哪？</p>
<p>,这个xml就是咱们需要的映射文件，它就可以体现出ORM，并且在这里面,也可以愉快的写sql语句</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><?xml version="1.0" encoding="UTF-8"?></span><br><span class="line"><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" </span><br><span class="line">"http://mybatis.org/dtd/mybatis-3-mapper.dtd"></span><br><span class="line"><!-- </span><br><span class="line"> 这个Mapper的主要功能就是写sql</span><br><span class="line"> mapper:根</span><br><span class="line"> namespace:命令空间 (用来确定唯一) 以前这个是可以不加的,现在必需加</span><br><span class="line"> namespace的值，规则的：映射文件XxxMapper.xml所在的包+domain类名+Mapper</span><br><span class="line"> --></span><br><span class="line"><mapper namespace="cn.itsource.mybatis.day1._1_hello.ProductMapper"></span><br><span class="line"> <!-- </span><br><span class="line"> select : 这里面写查询语句</span><br><span class="line"> id:用来确定这条sql语句的唯一</span><br><span class="line"> 以后我们确定唯一,也就是找sql语句 : namespace +.+ id</span><br><span class="line"> 例: cn.itsource.mybatis.day1._1_hello.ProductMapper.get</span><br><span class="line"> parameterType : 传入的参数类型 long:大Long _long:小long (具体的对应请参见文档)</span><br><span class="line"> resultType : 结果类型(第一条数据返回的对象类型) 自己的对象一定是全限定类名</span><br><span class="line"> --></span><br><span class="line"> <select id="get" parameterType="long" resultType="cn.itsource.domain.Product"></span><br><span class="line"> select * from product where id = #{id}</span><br><span class="line"> </select></span><br><span class="line"></mapper></span><br></pre></td></tr></table></figure>
<p>注意事项</p>
<p>我们的映射文件一般情况下是和它对应的domain实体类在同一个层级<br>② 这个映射文件的名称一般叫做 XxxMapper.xml (Xxx代表的是实体类名称)<br>③ namespace的名称为了确定唯一性，请大家根据我的要求取名<br> 如我们有一个类：<br> cn.itsource.domain.Product / cn.itsource.domain.Student<br> 那这里取名应该是：<br> cn.itsource.domain.ProductMapper /cn.itsource.domain.StudentMapper<br>④ 除了MyBatis支持的类型，其它的类型都通通使用全限定名 </p>
<p> 配置完后我们需要了解几个类<br> 2 拿到SqlSessionFactory之前需要读取核心的xml配置文件<br> 3 需要构造者(SqlSessionFactoryBuilder)来创建它</p>
<p>咱们说过，需要通过它去拿到一个SqlSession对象(相当于JDBC的连接)<br>必需要有SqlSession这个对象，我们才可以去执行相应的Sql</p>
<h2 id="这里使用一个简单的类与数据库表来测试一下"><a href="#这里使用一个简单的类与数据库表来测试一下" class="headerlink" title="这里使用一个简单的类与数据库表来测试一下"></a>这里使用一个简单的类与数据库表来测试一下</h2><p> <img src="https://img-blog.csdnimg.cn/20190801211818911.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2pjZXRwb29y,size_16,color_FFFFFF,t_70" alt="在这里插入图片描述">省略getset方法与tostring<br> 表<br> <img src="https://img-blog.csdnimg.cn/20190801211925878.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2pjZXRwb29y,size_16,color_FFFFFF,t_70" alt="在这里插入图片描述"></p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><!--命名空间--></span><br><span class="line"><mapper namespace="cn.itsource.dao.Productmaper"></span><br><span class="line"></span><br><span class="line"><!--查找所有--></span><br><span class="line"> <select id="findAll" resultType="Product"></span><br><span class="line"> select * from product</span><br><span class="line"> </select></span><br></pre></td></tr></table></figure>
<p> 写一个工具类</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line">public class MyBatisUtil {</span><br><span class="line"> private static SqlSessionFactory factory;</span><br><span class="line"></span><br><span class="line"> /**</span><br><span class="line"> * 静态代码块加载对象</span><br><span class="line"> */</span><br><span class="line"> static {</span><br><span class="line"> try {</span><br><span class="line"> //读取配置文件</span><br><span class="line"> Reader resourceAsReader = Resources.getResourceAsReader("mybatis-config.xml");</span><br><span class="line"> //创建工厂</span><br><span class="line"> factory = new SqlSessionFactoryBuilder().build(resourceAsReader);</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> } catch (Exception e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> System.err.println(e.getMessage()+"配置文件可能出错");</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> /**</span><br><span class="line"> * 获取sqlSession对象</span><br><span class="line"> * @return</span><br><span class="line"> */</span><br><span class="line"> public static SqlSession getSqlSessionInstance(){</span><br><span class="line"> return factory.openSession();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p> 测试类<br> <figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">@Test</span><br><span class="line"> public void testutil2() throws Exception {</span><br><span class="line"> SqlSession sqlSessionInstance = MyBatisUtil.getSqlSessionInstance();</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> List<Product> list = sqlSessionInstance</span><br><span class="line"> .selectList("cn.itsource.dao.Productmaper.findAll");</span><br><span class="line"> System.out.println(list);</span><br><span class="line"></span><br><span class="line"> }</span><br></pre></td></tr></table></figure></p>
<p> 测试无误<br> <img src="https://img-blog.csdnimg.cn/20190801212419633.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2pjZXRwb29y,size_16,color_FFFFFF,t_70" alt="在这里插入图片描述">`接下来写dao层crud</p>
<p> 接口<br> <figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line"> package cn.itsource.dao;</span><br><span class="line"></span><br><span class="line">import cn.itsource.domain.Product;</span><br><span class="line"></span><br><span class="line">import java.util.List;</span><br><span class="line"></span><br><span class="line">/**</span><br><span class="line"> * Product CRUD</span><br><span class="line"> */</span><br><span class="line">public interface IProductDao {</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> void delete(Long id);</span><br><span class="line"></span><br><span class="line"> void update(Product product);</span><br><span class="line"></span><br><span class="line"> void add(Product product);</span><br><span class="line"></span><br><span class="line"> List<Product> findall();</span><br><span class="line"></span><br><span class="line"> Product findOne(Long id);</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">`</span><br></pre></td></tr></table></figure></p>
<p> 实现类<br> <figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br></pre></td><td class="code"><pre><span class="line"> package cn.itsource.dao.impl;</span><br><span class="line"></span><br><span class="line">import cn.itsource.dao.IProductDao;</span><br><span class="line">import cn.itsource.domain.Product;</span><br><span class="line">import cn.itsource.utils.MyBatisUtil;</span><br><span class="line">import org.apache.ibatis.session.SqlSession;</span><br><span class="line"></span><br><span class="line">import java.util.List;</span><br><span class="line"></span><br><span class="line">/**</span><br><span class="line"> * CRUD </span><br><span class="line"> */</span><br><span class="line">public class ProductDaoImpl implements IProductDao {</span><br><span class="line"> public static final String NAMESPACE = "cn.itsource.dao.Productmaper.";</span><br><span class="line"></span><br><span class="line"> @Override</span><br><span class="line"> public void delete(Long id) {</span><br><span class="line"> SqlSession session = MyBatisUtil.getSqlSessionInstance();</span><br><span class="line"> try {</span><br><span class="line"> session.delete(NAMESPACE + "delete", id);</span><br><span class="line"> session.commit();</span><br><span class="line"> } catch (Exception e) {</span><br><span class="line"> session.rollback();</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> } finally {</span><br><span class="line"> session.close();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> @Override</span><br><span class="line"> public void update(Product product) {</span><br><span class="line"> SqlSession session = MyBatisUtil.getSqlSessionInstance();</span><br><span class="line"> try {</span><br><span class="line"> session.update(NAMESPACE + "update", product);</span><br><span class="line"> session.commit();</span><br><span class="line"> } catch (Exception e) {</span><br><span class="line"> session.rollback();</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> } finally {</span><br><span class="line"> session.close();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> @Override</span><br><span class="line"> public void add(Product product) {</span><br><span class="line"> SqlSession session = MyBatisUtil.getSqlSessionInstance();</span><br><span class="line"> try {</span><br><span class="line"> session.insert("cn.itsource.dao.Productmaper.add", product);</span><br><span class="line"> session.commit();</span><br><span class="line"> } catch (Exception e) {</span><br><span class="line"> session.rollback();</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }finally {</span><br><span class="line"> session.close();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> @Override</span><br><span class="line"> public List<Product> findall() {</span><br><span class="line"> try {</span><br><span class="line"> return MyBatisUtil.getSqlSessionInstance().selectList("cn.itsource.dao.Productmaper.findAll");</span><br><span class="line"> } catch (Exception e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> return null;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> @Override</span><br><span class="line"> public Product findOne(Long id) {</span><br><span class="line"> try {</span><br><span class="line"> return MyBatisUtil.getSqlSessionInstance().selectOne("cn.itsource.dao.Productmaper.findOne", id);</span><br><span class="line"> } catch (Exception e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> return null;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>在配置文件中写sql</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br></pre></td><td class="code"><pre><span class="line"><?xml version="1.0" encoding="UTF-8" ?></span><br><span class="line"><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"</span><br><span class="line"> "http://mybatis.org/dtd/mybatis-3-mapper.dtd"></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><!--命名空间--></span><br><span class="line"><mapper namespace="cn.itsource.dao.Productmaper"></span><br><span class="line"></span><br><span class="line"><!--查找一个--></span><br><span class="line"> <select id="findOne" parameterType="long" resultType="cn.itsource.domain.Product"></span><br><span class="line"> select * from product where id = #{id}</span><br><span class="line"> </select></span><br><span class="line"><!-- 查询所有 的sql --></span><br><span class="line"> <select id="findAll" resultType="Product"></span><br><span class="line"> select * from product</span><br><span class="line"> </select></span><br><span class="line"><!-- 添加sql --></span><br><span class="line"> <!--useGeneratedKeys="true" keyColumn="id" keyProperty="id" 添加后获取主键 --></span><br><span class="line"> <insert id="add" parameterType="cn.itsource.domain.Product" useGeneratedKeys="true" keyColumn="id" keyProperty="id"></span><br><span class="line"> INSERT INTO product</span><br><span class="line"> (productName,dir_id,salePrice,supplier,brand,cutoff,costPrice)</span><br><span class="line"> values</span><br><span class="line"> (#{productName},#{dir_id},#{salePrice},#{supplier},#{brand},#{cutoff},#{costPrice})</span><br><span class="line"> </insert></span><br><span class="line"><!-- 删除sql --></span><br><span class="line"> <delete id="delete" parameterType="long"></span><br><span class="line"> delete from product where id = #{id}</span><br><span class="line"> </delete></span><br><span class="line"><!-- 更新sql --></span><br><span class="line"> <update id="update" parameterType="cn.itsource.domain.Product"></span><br><span class="line"> update product</span><br><span class="line"> set productName = #{productName},</span><br><span class="line"> dir_id = #{dir_id},</span><br><span class="line"> salePrice = #{salePrice},</span><br><span class="line"> supplier = #{supplier},</span><br><span class="line"> brand = #{brand},</span><br><span class="line"> cutoff = #{cutoff},</span><br><span class="line"> costPrice = #{costPrice}</span><br><span class="line"> where id = #{id}</span><br><span class="line"> </update></span><br><span class="line"></span><br><span class="line"></mapper></span><br></pre></td></tr></table></figure>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br></pre></td><td class="code"><pre><span class="line"> 测试类</span><br><span class="line">package cn.itsource.Test;</span><br><span class="line"></span><br><span class="line">import cn.itsource.dao.IProductDao;</span><br><span class="line">import cn.itsource.dao.impl.ProductDaoImpl;</span><br><span class="line">import cn.itsource.domain.Product;</span><br><span class="line">import cn.itsource.utils.MyBatisUtil;</span><br><span class="line">import org.apache.ibatis.io.Resources;</span><br><span class="line">import org.apache.ibatis.session.SqlSession;</span><br><span class="line">import org.apache.ibatis.session.SqlSessionFactoryBuilder;</span><br><span class="line">import org.junit.Test;</span><br><span class="line"></span><br><span class="line">import java.io.Reader;</span><br><span class="line">import java.util.List;</span><br><span class="line"></span><br><span class="line">public class MybatisimplTest {</span><br><span class="line"> @Test</span><br><span class="line"> public void test() throws Exception {</span><br><span class="line"> IProductDao productDao = new ProductDaoImpl();</span><br><span class="line"> List<Product> findall = productDao.findall();</span><br><span class="line"> findall.forEach( v -> System.out.println(v));</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> @Test</span><br><span class="line"> public void testfindone() throws Exception {</span><br><span class="line"> IProductDao productDao = new ProductDaoImpl();</span><br><span class="line"> Product one = productDao.findOne(1L);</span><br><span class="line"> System.out.println(one);</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line"> @Test</span><br><span class="line"> public void testadd() throws Exception {</span><br><span class="line"> IProductDao productDao = new ProductDaoImpl();</span><br><span class="line"> Product one1 = productDao.findOne(2L);</span><br><span class="line"> one1.setId(null);</span><br><span class="line"> productDao.add(one1);</span><br><span class="line"> System.out.println(one1);</span><br><span class="line"> }</span><br><span class="line"> @Test</span><br><span class="line"> public void testupdate() throws Exception {</span><br><span class="line"> IProductDao productDao = new ProductDaoImpl();</span><br><span class="line"> Product one1 = productDao.findOne(1L);</span><br><span class="line"> one1.setProductName("张扬");</span><br><span class="line"> productDao.update(one1);</span><br><span class="line"> }</span><br><span class="line"> @Test</span><br><span class="line"> public void testdelete() throws Exception {</span><br><span class="line"> IProductDao productDao = new ProductDaoImpl();</span><br><span class="line"> productDao.delete(1L);</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>crud注意事项</p>
<p>下面的点都很重要，是大家在使用MyBatis的时候经常出现的点。希望大家引起重视。出现问题的时候心态放平,不要狂躁,慢慢的找。基本咱们使用MyBatis中出的错都在这里。<br>使用框架的时候配置信息变多，在配置里写的都是字符串，而且经常是要对应的。因为，这里希望大家要切记：写的时候细心，出现错误找字符串要耐心，<br> 1 主配置中未配置相应的mapper(当然，这个路径也可能写错)<br> 2 在代码中调用Sql的时候路径写错<br> 3 Sql写错,这个应该还好找<br> 4 当我们在配置文件中很多地方如果写错，即便是你还没有使用也可能会报错<br> 5 写Sql的标签不需要全部一致(如添加不一定必需使用insert),但是它的属性会不同<br> 6 在传入与返回参数时全限定类名写错<br> 在开发的时候，要边做边测试。 在某一步出现错误后，删除新加的代码看有没有问题，如果删除部分代码后运行成功，就相应的可以缩小排错的范围。</p>
<h4 id="SqlSessionFactoryBuilder"><a href="#SqlSessionFactoryBuilder" class="headerlink" title="SqlSessionFactoryBuilder"></a>SqlSessionFactoryBuilder</h4><p>建造者模式:我们最后拿到的这个对象是非常复杂的. 用这个建造者就它先为我们把这些复杂的代码完成.<br>这个类可以被实例化，使用和丢弃。一旦你创建了SqlSessionFactory后，这个SqlSessionFactoryBuilder类就不需要存在了。因此SqlSessionFactoryBuilder实例的最佳范围是方法范围（也就是本地方法变量）。<br>你可以重用SqlSessionFactoryBuilder来创建多个SqlSessionFactory实例，但是最好的方式是<br>不需要保持它一直存在来保证所有XML解析资源，因为还有更重要的事情要做。<br> <strong>总结来说就是用完可以随意丢弃且只用一次,</strong></p>
<h4 id="SqlSessionFactory-类似于jpa的EntityMangerFactory"><a href="#SqlSessionFactory-类似于jpa的EntityMangerFactory" class="headerlink" title="SqlSessionFactory(类似于jpa的EntityMangerFactory)"></a>SqlSessionFactory(类似于jpa的EntityMangerFactory)</h4><p> 一旦被创建，SqlSessionFactory应该在你的应用执行期间都存在。没有理由来处理或重新创建它。使用SqlSessionFactory的最佳实践是在应用运行期间不要重复创建多次<br>** 是一个重量级对象 , 我们使用静态代码块单例模式**</p>
<h4 id="SqlSession"><a href="#SqlSession" class="headerlink" title="SqlSession"></a>SqlSession</h4><p>每个线程都应该有它自己的SqlSession实例。SqlSession的实例不能被共享，也是线程不安全的。因此最佳的范围是请求或方法范围。<br><strong>绝对不能将SqlSession实例的引用放在一个类的静态字段甚至是实例字段中。<br>也绝不能将SqlSession实例的引用放在任何类型的管理范围中，比如Serlvet架构中的HttpSession。</strong></p>
<p>如果你现在正用任意的Web框架，要考虑SqlSession放在一个和HTTP请求对象相似的范围内。换句话说，基于收到的HTTP请求，你可以打开了一个SqlSession，然后返回响应，就可以关闭它了。关闭Session很重要， </p>
<h3 id="列名与属性名不对应的解决方案-resultMap"><a href="#列名与属性名不对应的解决方案-resultMap" class="headerlink" title="列名与属性名不对应的解决方案 resultMap"></a>列名与属性名不对应的解决方案 resultMap</h3><p>大家应该有注意到，前面咱们做映射文件的时候，只做了表与对象之间的联系。并没有做列与字段之间的联系。那么它们之间是怎么联系上的呢？<br>由于之前咱们的列名与属性名是一样的，因此框架进行了自动的识别。<br>那么：如果咱们的列名与属性名不一致了(对应不上)，这时候应该怎么办呢？<br>这时候，就需要我们开发人员告诉MyBatis，我们需要把哪些列名与属性名对应上。</p>
<p><img src="https://img-blog.csdnimg.cn/20190801213637960.png" alt="在这里插入图片描述"></p>
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<a href="/2017/07/02/部分的知识/" class="article-date">
<time datetime="2017-07-02T12:53:52.000Z" itemprop="datePublished">2017-07-02</time>
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<a class="article-title" href="/2017/07/02/部分的知识/">关于注解部分的知识</a>
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<p>所有关于注解的文章都绕不开这四个注解,我们也不例外<br>@Target<br>@Retention<br>@Documented<br>@Inherited<br>接下来就一个个的介绍<br>首先是 <strong>@Target</strong><br>这个注解用来标志当前定义的注解是打在哪个位置的,比如类上,方法上,字段上,可以写多个<br>通过源码我们可以看到内部是一个数组,所有可以写多个</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">@Documented</span><br><span class="line">@Retention(RetentionPolicy.RUNTIME)</span><br><span class="line">@Target(ElementType.ANNOTATION_TYPE)</span><br><span class="line">public @interface Target {</span><br><span class="line"> /**</span><br><span class="line"> * Returns an array of the kinds of elements an annotation type</span><br><span class="line"> * can be applied to.</span><br><span class="line"> * @return an array of the kinds of elements an annotation type</span><br><span class="line"> * can be applied to</span><br><span class="line"> *数组表示此属性可以写多个值</span><br><span class="line"> */</span><br><span class="line"> ElementType[] value();</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>它可以使用的值有以下这些<br><img src="https://img-blog.csdnimg.cn/20190913031812404.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2pjZXRwb29y,size_16,color_FFFFFF,t_70" alt="在这里插入图片描述"><br>ElementType是一个枚举类内部就是上面列举出的几个属性当然,也可以不用这个枚举,直接写字符串效果是一样的<br>那么他们分别代表什么呢<br>TYPE:类、接口(包括注解类型) 或enum声明。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"> FIELD:字段声明(包括enum常量).,也就是打在字段上</span><br><span class="line"></span><br><span class="line"> METHOD:方法声明。</span><br><span class="line"></span><br><span class="line"> PARAMTER:形式参数声明。,方法的形参上</span><br><span class="line"></span><br><span class="line"> CONSTRUCTOR:构造函数声明。constructort上</span><br><span class="line"></span><br><span class="line"> LOCAL_VARIABLE：局部变量声明。方法内变量</span><br><span class="line"></span><br><span class="line"> ANNOTATION_TYPE：注解类型声明。打在注解上</span><br><span class="line"></span><br><span class="line"> PACKAGE：包声明</span><br><span class="line"></span><br><span class="line"> TYPE_PARAMETER：参数类型声明</span><br><span class="line"></span><br><span class="line"> TYPE_USE:使用一个类型，详见：java.lang.annotation.ElementType</span><br></pre></td></tr></table></figure>
<p><strong>@Retention 注解</strong><br>指的是注解的生命周期<br>即会保留到哪个阶段。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">SOURCE：源码级别保留，编译后即丢弃。</span><br><span class="line">CLASS:编译级别保留，编译后的class文件中存在，在jvm运行时丢弃，这是默认值。</span><br><span class="line">RUNTIME： 运行级别保留，编译后的class文件中存在，在jvm运行时保留，可以被反射调用。</span><br></pre></td></tr></table></figure>
<p><strong>@Documented 注解</strong><br>能被javadoc此类的工具文档化 无值<br><strong>@Inherited注解</strong><br>当你想让你的自定义注解被继承时,可以使用这个注解,也没有参数取值</p>
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<article id="page-oop" class="article article-type-page" itemscope itemprop="blogPost">
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<time datetime="2017-04-21T12:40:43.000Z" itemprop="datePublished">2017-04-21</time>
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<a class="article-title" href="/2017/04/21/oop/">JAVA面向对象</a>
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<h2 id="JAVA面向对象的思维"><a href="#JAVA面向对象的思维" class="headerlink" title="JAVA面向对象的思维"></a>JAVA面向对象的思维</h2><pre><code>面向对象三大基本特征：封装、继承、多态。而面向对象的过程就是围绕对象进行工作的过程。
类是一种数据类型
对象则是这种类型的一个具体实例</code></pre><p>对象分为两个部分，动态部分【行为】与静态部分[描述]。</p>
<p>①静态部分：顾名思义就是不能动的部分，这个部分被称为“属性”，任何对象都会具备其自身属性，如一个人，它包括高矮、胖瘦、性别、年龄等属性。<br>②动态部分：具有这些属性的人会执行哪些动作这个人可以哭泣、微笑、说话、行走，这些是这个人具备的行为（动态部分），<br>.Java语言的设计思想：希望将现实生活中的，对象与对象之间的关系在计算机系统得以体现，从而构建计算机系统<br> 对于事物的思考：需要类，需要对象【万事万物皆对象 万事万物皆可分类】<br> 类：对于类思考：万事万物简单思考：<br> 类：具备两大特性【属性】<br> 1.静态属性：信息描述，学生，姓名，年龄 ，身高<br> 2.动态行为：处理数据，人来说：会走，会跑……</p>
<p><strong>封装</strong><br>通过给类中的成员（字段，方法，构造方法）添加访问权限来实现访问控制</p>
<p><strong>继承</strong><br>(1)泛化和特化<br> <em>①泛华：在多个子类的基础上面抽取共有属性的行为到一个父类中去<br> ②特化：在一个父类的基础上拓展子类特有的属性和行为，生成一个新的子类<br> ③原则：父类存放共性，子类存放特性</em><br>(2)Java中类的继承特点<br> <em>①Java中类的继承是单继承<br> ②可以支持多重继承每一个类都//也就是间接继承<br> ③有一个直接父类,如果没有看到显示的继承代码,那么就隐式继承就Object</em><br>(3)继承到父类的那些东西<br> <em>①非私有的字段及方法<br> ②父类特性<br> ③静态方法不能被覆写</em><br>1)如果是父类装子类对象调父类和子类都有的静态方法，会调用父类方法</p>
<p><strong>多态</strong><br>(1)一种事物的多种形态<br>(2)使用aml：装入子类对象存在多种可能性：<br>(3)编译是看的是Animal类型【只看类型不看值】<br>(4)运行时看的是实际存放的对象【真实类型】<br>(5)官方概念：编译时跟运行时类型不一致就产生了多态<br>(6)民间理解：父类类型的变量，存放子类类型的对象，可能存放子类类型的对象有多种可能<br>(7)多态存在的前提：必须有继承关系<br>(8)多态应用<br>①方法参数传递：方法形参父类类型，允许传子类类型对象<br>②方法返回值<br>(9)多态的好处：<br>①屏蔽了不同子类之间实现的差异<br>(10)加强面向对象编程思想：<br>①此处体现java语言设计思想，希望将现实生活中的对象与对象之间的关系在计算机系统得以体现</p>
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<article id="post-JAVA中-与equals的区别" class="article article-type-post" itemscope itemprop="blogPost">
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<a href="/2017/03/21/JAVA中-与equals的区别/" class="article-date">
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<a class="article-title" href="/2017/03/21/JAVA中-与equals的区别/">JAVA中==与equals的区别</a>
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<p> == 和 equals 都是比较是否相等,请问它们到底有什么区别呢?<br>相等 :<br> 传统的理解一般都是数字值是否相等;<br>在程序中任何东西都是数据,都会比较是否相等[ 对象 ]<br> == 比较运算符<br>基本数据类型变量: 比较的就是值是否相等;<br>引用数据类型变量: 比较的是对象的地址是否一样;（排除特殊 String）<br> equals 方法[最初定义在根类Object中的,比较对象是否相等]<br> 基本数据类型 : 不能够使用! 基本数据类型不是对象,不能够调用Object中的方法<br> 引用数据类型 : 但是在Object的源码中定义的就是 == 进行比较比较<br>定义好的类没有覆写过equals方法，则会直接调用到了Object中的equals方法,那么本质还是在使用==比较<br>在实际开发中,自定义类：一般比较对象，都是通过对象的属性值进行比较,所以自定义类，会经常覆写Object中的此方法,把自己的比较规则写在方法里面;<br>⑫覆写equals方法的意义：定义类，覆写equals方法，自己制定规则，比较自定义类对象的静态属性<br>(5)打印过程实际上调用了toString方法</p>
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