bump to java21

Author: eschultink

.github/workflows/test-java.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: 'adopt'
-          java-version: '17' # maven won't accept --release argument with java < 8; and 11 is next LTS
+          java-version: '21' # maven won't accept --release argument with java < 8; and 11 is next LTS
       - id: 'read-cache-maven-packages'
         name: Read Cached Maven packages
         uses: actions/cache@v4
@@ -56,7 +56,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: 'adopt'
-          java-version: '17' # maven won't accept --release argument with java < 8; and 11 is next LTS
+          java-version: '21' # maven won't accept --release argument with java < 8; and 11 is next LTS
       - id: 'read-cache-maven-packages'
         name: Read Cached Maven packages
         uses: actions/cache@v4

java/pom.xml

@@ -41,9 +41,8 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.13.0</version>
         <configuration>
-          <source>17</source>
-          <target>17</target>
-
+          <source>21</source>
+          <target>21</target>
         </configuration>
       </plugin>
       <plugin>