feat: add Apache HttpClient 5.x adapter for Sentinel

Add sentinel-apache-httpclient5-adapter module that integrates Sentinel
flow control with Apache HttpClient 5.x outgoing HTTP requests.

Features:
- ExecChainHandler-based integration (SentinelApacheHttpClient5Handler)
- Configurable resource name extraction (METHOD:URL format by default)
- Query string and fragment stripping in resource names
- Customizable fallback handling (throws SentinelRpcException by default)
- Configurable resource name prefix (default: "httpclient:")

Follows the same architecture pattern as the existing HttpClient 4.x
adapter while adapting to HC5's ExecChainHandler API.

Closes #3614

Change-Id: I966295da9419beac99451fc6c9c31b1d75a9e7e6
Co-developed-by: Cursor <noreply@cursor.com>

Author: uuuyuqi

sentinel-adapter/pom.xml

@@ -21,6 +21,7 @@
         <module>sentinel-apache-dubbo-adapter</module>
         <module>sentinel-apache-dubbo3-adapter</module>
         <module>sentinel-apache-httpclient-adapter</module>
+        <module>sentinel-apache-httpclient5-adapter</module>
         <module>sentinel-sofa-rpc-adapter</module>
         <module>sentinel-grpc-adapter</module>
         <module>sentinel-zuul-adapter</module>

sentinel-adapter/sentinel-apache-httpclient5-adapter/README.md

@@ -0,0 +1,77 @@
+# Sentinel Apache HttpClient 5.x Adapter
+
+## Introduction
+
+Sentinel provides integration for Apache HttpClient 5.x to enable flow control for outgoing HTTP requests.
+
+## Usage
+
+### Add dependency
+
+```xml
+<dependency>
+    <groupId>com.alibaba.csp</groupId>
+    <artifactId>sentinel-apache-httpclient5-adapter</artifactId>
+    <version>x.y.z</version>
+</dependency>
+```
+
+### Build the HttpClient
+
+```java
+CloseableHttpClient httpclient = HttpClients.custom()
+    .addExecInterceptorBefore(ChainElement.MAIN_TRANSPORT.name(), "sentinel",
+        new SentinelApacheHttpClient5Handler())
+    .build();
+```
+
+Or with custom configuration:
+
+```java
+SentinelApacheHttpClientConfig config = new SentinelApacheHttpClientConfig();
+config.setPrefix("httpclient:");
+config.setExtractor(myExtractor);
+config.setFallback(myFallback);
+
+CloseableHttpClient httpclient = HttpClients.custom()
+    .addExecInterceptorBefore(ChainElement.MAIN_TRANSPORT.name(), "sentinel",
+        new SentinelApacheHttpClient5Handler(config))
+    .build();
+```
+
+### Configuration
+
+| Name | Description | Type | Default Value |
+|------|------------|------|---------------|
+| prefix | Customize resource prefix | `String` | `httpclient:` |
+| extractor | Customize resource extractor | `ApacheHttpClientResourceExtractor` | `DefaultApacheHttpClientResourceExtractor` |
+| fallback | Handle request when it is blocked | `ApacheHttpClientFallback` | `DefaultApacheHttpClientFallback` |
+
+### Resource Extractor
+
+The default extractor generates resource names in the format `METHOD:url` (e.g. `GET:http://example.com/api/users`),
+with query parameters and fragments stripped. You can customize this by implementing `ApacheHttpClientResourceExtractor`:
+
+```java
+public class MyResourceExtractor implements ApacheHttpClientResourceExtractor {
+    @Override
+    public String extractor(ClassicHttpRequest request) {
+        // custom resource name extraction logic
+        return request.getMethod() + ":" + request.getRequestUri();
+    }
+}
+```
+
+### Fallback
+
+The default fallback throws `SentinelRpcException`. You can customize the behavior:
+
+```java
+public class MyFallback implements ApacheHttpClientFallback {
+    @Override
+    public ClassicHttpResponse handle(ClassicHttpRequest request, BlockException e) {
+        // return a custom response or throw exception
+        throw new SentinelRpcException(e);
+    }
+}
+```

sentinel-adapter/sentinel-apache-httpclient5-adapter/pom.xml

@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <groupId>com.alibaba.csp</groupId>
+        <artifactId>sentinel-adapter</artifactId>
+        <version>${revision}</version>
+        <relativePath>../pom.xml</relativePath>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <name>${project.groupId}:${project.artifactId}</name>
+
+    <artifactId>sentinel-apache-httpclient5-adapter</artifactId>
+    <packaging>jar</packaging>
+
+    <properties>
+        <apache.httpclient5.version>5.1</apache.httpclient5.version>
+        <spring.boot.version>2.1.3.RELEASE</spring.boot.version>
+        <spring-test.version>5.1.5.RELEASE</spring-test.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.alibaba.csp</groupId>
+            <artifactId>sentinel-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.httpcomponents.client5</groupId>
+            <artifactId>httpclient5</artifactId>
+            <version>${apache.httpclient5.version}</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.alibaba</groupId>
+            <artifactId>fastjson</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+            <version>${spring.boot.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-test</artifactId>
+            <version>${spring.boot.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-test</artifactId>
+            <version>${spring-test.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>

sentinel-adapter/sentinel-apache-httpclient5-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/apache/httpclient5/SentinelApacheHttpClient5Handler.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright 1999-2020 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.adapter.apache.httpclient5;
+
+import com.alibaba.csp.sentinel.Entry;
+import com.alibaba.csp.sentinel.EntryType;
+import com.alibaba.csp.sentinel.ResourceTypeConstants;
+import com.alibaba.csp.sentinel.SphU;
+import com.alibaba.csp.sentinel.Tracer;
+import com.alibaba.csp.sentinel.adapter.apache.httpclient5.config.SentinelApacheHttpClientConfig;
+import com.alibaba.csp.sentinel.slots.block.BlockException;
+import com.alibaba.csp.sentinel.util.StringUtil;
+import org.apache.hc.client5.http.classic.ExecChain;
+import org.apache.hc.client5.http.classic.ExecChainHandler;
+import org.apache.hc.core5.http.ClassicHttpRequest;
+import org.apache.hc.core5.http.ClassicHttpResponse;
+import org.apache.hc.core5.http.HttpException;
+
+import java.io.IOException;
+
+/**
+ * Apache HttpClient 5.x adapter for Sentinel.
+ *
+ * <p>This handler implements {@link ExecChainHandler} to intercept outgoing HTTP requests
+ * and protect them with Sentinel flow control.</p>
+ *
+ * <p>Usage example:</p>
+ * <pre>{@code
+ * CloseableHttpClient httpclient = HttpClients.custom()
+ *     .addExecInterceptorBefore(ChainElement.MAIN_TRANSPORT.name(), "sentinel",
+ *         new SentinelApacheHttpClient5Handler())
+ *     .build();
+ * }</pre>
+ *
+ * @author qihuai.wyq
+ */
+public class SentinelApacheHttpClient5Handler implements ExecChainHandler {
+
+    private final SentinelApacheHttpClientConfig config;
+
+    public SentinelApacheHttpClient5Handler() {
+        this.config = new SentinelApacheHttpClientConfig();
+    }
+
+    public SentinelApacheHttpClient5Handler(SentinelApacheHttpClientConfig config) {
+        this.config = config;
+    }
+
+    @Override
+    public ClassicHttpResponse execute(ClassicHttpRequest classicHttpRequest, ExecChain.Scope scope,
+                                       ExecChain execChain) throws IOException, HttpException {
+        String name = config.getExtractor().extractor(classicHttpRequest);
+        if (StringUtil.isEmpty(name)) {
+            return execChain.proceed(classicHttpRequest, scope);
+        }
+
+        if (StringUtil.isNotEmpty(config.getPrefix())) {
+            name = config.getPrefix() + name;
+        }
+
+        Entry entry = null;
+        try {
+            entry = SphU.entry(name, ResourceTypeConstants.COMMON_WEB, EntryType.OUT);
+            return execChain.proceed(classicHttpRequest, scope);
+        } catch (BlockException e) {
+            return config.getFallback().handle(classicHttpRequest, e);
+        } catch (IOException | HttpException | RuntimeException e) {
+            Tracer.traceEntry(e, entry);
+            throw e;
+        } catch (Throwable t) {
+            Tracer.traceEntry(t, entry);
+            throw new RuntimeException(t);
+        } finally {
+            if (entry != null) {
+                entry.exit();
+            }
+        }
+    }
+}

sentinel-adapter/sentinel-apache-httpclient5-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/apache/httpclient5/config/SentinelApacheHttpClientConfig.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 1999-2020 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.adapter.apache.httpclient5.config;
+
+import com.alibaba.csp.sentinel.adapter.apache.httpclient5.extractor.ApacheHttpClientResourceExtractor;
+import com.alibaba.csp.sentinel.adapter.apache.httpclient5.extractor.DefaultApacheHttpClientResourceExtractor;
+import com.alibaba.csp.sentinel.adapter.apache.httpclient5.fallback.ApacheHttpClientFallback;
+import com.alibaba.csp.sentinel.adapter.apache.httpclient5.fallback.DefaultApacheHttpClientFallback;
+import com.alibaba.csp.sentinel.util.AssertUtil;
+
+/**
+ * @author qihuai.wyq
+ */
+public class SentinelApacheHttpClientConfig {
+
+    private String prefix = "httpclient:";
+    private ApacheHttpClientResourceExtractor extractor = new DefaultApacheHttpClientResourceExtractor();
+    private ApacheHttpClientFallback fallback = new DefaultApacheHttpClientFallback();
+
+    public String getPrefix() {
+        return prefix;
+    }
+
+    public void setPrefix(String prefix) {
+        AssertUtil.notNull(prefix, "prefix cannot be null");
+        this.prefix = prefix;
+    }
+
+    public ApacheHttpClientResourceExtractor getExtractor() {
+        return extractor;
+    }
+
+    public void setExtractor(ApacheHttpClientResourceExtractor extractor) {
+        AssertUtil.notNull(extractor, "extractor cannot be null");
+        this.extractor = extractor;
+    }
+
+    public ApacheHttpClientFallback getFallback() {
+        return fallback;
+    }
+
+    public void setFallback(ApacheHttpClientFallback fallback) {
+        AssertUtil.notNull(fallback, "fallback cannot be null");
+        this.fallback = fallback;
+    }
+}

sentinel-adapter/sentinel-apache-httpclient5-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/apache/httpclient5/extractor/ApacheHttpClientResourceExtractor.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 1999-2020 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.adapter.apache.httpclient5.extractor;
+
+import org.apache.hc.core5.http.ClassicHttpRequest;
+
+/**
+ * Extracts Sentinel resource name from an Apache HttpClient 5.x request.
+ *
+ * @author qihuai.wyq
+ */
+public interface ApacheHttpClientResourceExtractor {
+
+    /**
+     * Extract resource name from the given request.
+     *
+     * @param request the HTTP request
+     * @return the resource name, or {@code null}/{@code ""} to skip Sentinel protection
+     */
+    String extractor(ClassicHttpRequest request);
+}