upgrade to java 21

Author: stevehu

pom.xml

@@ -76,7 +76,7 @@
     </pluginRepositories>
 
     <properties>
-        <java.version>11</java.version>
+        <java.version>21</java.version>
         <maven.compiler.source>${java.version}</maven.compiler.source>
         <maven.compiler.target>${java.version}</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>