Require Java 21 or newer

As Java 25 is available for a couple of months now,
it is time to drop support for Java 17. Starting with this commit, Jenkins supports only Java 21 and 25, or newer.

See https://www.jenkins.io/blog/2023/11/06/introducing-2-2-2-java-support-plan/.

Author: uhafner

core/src/main/java/jenkins/monitor/JavaVersionRecommendationAdminMonitor.java

@@ -78,7 +78,6 @@ public class JavaVersionRecommendationAdminMonitor extends AdministrativeMonitor
 
     static {
         NavigableMap<Integer, LocalDate> supportedVersions = new TreeMap<>();
-        supportedVersions.put(17, LocalDate.of(2026, 3, 31)); // Temurin: 2027-10-31
         supportedVersions.put(21, LocalDate.of(2027, 9, 30)); // Temurin: 2029-09-30
         supportedVersions.put(25, LocalDate.of(2029, 9, 30)); // Temurin: 2031-09-30
         SUPPORTED_JAVA_VERSIONS = Collections.unmodifiableNavigableMap(supportedVersions);

war/pom.xml

@@ -133,7 +133,6 @@ THE SOFTWARE.
   <build>
     <finalName>jenkins</finalName>
     <plugins>
-      <!-- TODO When Java 11 usage declines to a terminal level, this can be deleted. -->
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
@@ -143,43 +142,10 @@ THE SOFTWARE.
             <configuration>
               <rules>
                 <requireJavaVersion>
-                  <version>11</version>
+                  <version>21</version>
                 </requireJavaVersion>
                 <enforceBytecodeVersion>
-                  <maxJdkVersion>11</maxJdkVersion>
-                  <excludes>
-                    <exclude>io.jenkins.tools:bridge-method-annotation</exclude>
-                    <exclude>org.jenkins-ci:annotation-indexer</exclude>
-                    <exclude>org.jenkins-ci:commons-jelly</exclude>
-                    <exclude>org.jenkins-ci:commons-jelly-tags-fmt</exclude>
-                    <exclude>org.jenkins-ci:commons-jelly-tags-xml</exclude>
-                    <exclude>org.jenkins-ci:crypto-util</exclude>
-                    <exclude>org.jenkins-ci.main:cli</exclude>
-                    <exclude>org.jenkins-ci.main:jenkins-core</exclude>
-                    <exclude>org.jenkins-ci.main:remoting</exclude>
-                    <exclude>org.jenkins-ci.main:websocket-jetty12-ee9</exclude>
-                    <exclude>org.jenkins-ci.main:websocket-spi</exclude>
-                    <exclude>org.jenkins-ci:memory-monitor</exclude>
-                    <exclude>org.jenkins-ci:symbol-annotation</exclude>
-                    <exclude>org.jenkins-ci:task-reactor</exclude>
-                    <exclude>org.jenkins-ci:version-number</exclude>
-                    <exclude>org.jvnet.hudson:commons-jelly-tags-define</exclude>
-                    <exclude>org.jvnet.winp:winp</exclude>
-                    <exclude>org.kohsuke:access-modifier-annotation</exclude>
-                    <exclude>org.kohsuke.stapler:json-lib</exclude>
-                    <exclude>org.kohsuke.stapler:stapler</exclude>
-                    <exclude>org.kohsuke.stapler:stapler-groovy</exclude>
-                    <exclude>org.kohsuke.stapler:stapler-jelly</exclude>
-                    <exclude>org.springframework.security:spring-security-core</exclude>
-                    <exclude>org.springframework.security:spring-security-crypto</exclude>
-                    <exclude>org.springframework.security:spring-security-web</exclude>
-                    <exclude>org.springframework:spring-aop</exclude>
-                    <exclude>org.springframework:spring-beans</exclude>
-                    <exclude>org.springframework:spring-context</exclude>
-                    <exclude>org.springframework:spring-core</exclude>
-                    <exclude>org.springframework:spring-expression</exclude>
-                    <exclude>org.springframework:spring-web</exclude>
-                  </excludes>
+                  <maxJdkVersion>21</maxJdkVersion>
                 </enforceBytecodeVersion>
               </rules>
             </configuration>
@@ -190,15 +156,15 @@ THE SOFTWARE.
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
         <configuration>
-          <release>11</release>
-          <testRelease>11</testRelease>
+          <release>21</release>
+          <testRelease>21</testRelease>
         </configuration>
       </plugin>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
         <configuration>
-          <release>11</release>
+          <release>21</release>
         </configuration>
       </plugin>
       <plugin>

war/src/main/java/executable/Main.java

@@ -76,7 +76,7 @@ public class Main {
      * This list must remain synchronized with the one in {@code
      * JavaVersionRecommendationAdminMonitor}.
      */
-    private static final NavigableSet<Integer> SUPPORTED_JAVA_VERSIONS = new TreeSet<>(List.of(17, 21, 25));
+    private static final NavigableSet<Integer> SUPPORTED_JAVA_VERSIONS = new TreeSet<>(List.of(21, 25));
 
     /**
      * Sets custom session cookie name.

war/src/test/java/executable/MainTest.java

@@ -13,26 +13,26 @@ void unsupported() {
         assertJavaCheckFails(8, true);
         assertJavaCheckFails(11, false);
         assertJavaCheckFails(11, true);
+        assertJavaCheckFails(17, false);
+        assertJavaCheckFails(17, true);
     }
 
     @Test
     void supported() {
-        assertJavaCheckPasses(17, false);
-        assertJavaCheckPasses(17, true);
         assertJavaCheckPasses(21, false);
         assertJavaCheckPasses(21, true);
+        assertJavaCheckPasses(25, false);
+        assertJavaCheckPasses(25, true);
     }
 
     @Test
     void future() {
-        assertJavaCheckFails(18, false);
-        assertJavaCheckFails(19, false);
-        assertJavaCheckFails(20, false);
         assertJavaCheckFails(22, false);
-        assertJavaCheckPasses(18, true);
-        assertJavaCheckPasses(19, true);
-        assertJavaCheckPasses(20, true);
+        assertJavaCheckFails(23, false);
+        assertJavaCheckFails(24, false);
         assertJavaCheckPasses(22, true);
+        assertJavaCheckPasses(23, true);
+        assertJavaCheckPasses(24, true);
     }
 
     private static void assertJavaCheckFails(int releaseVersion, boolean enableFutureJava) {