Update to support JDK 21+ with matrix builds

- Changed GitHub Actions to use matrix strategy for JDK 21, 22, 23, 24
- Updated Maven configuration to target JDK 21 as minimum
- Updated README to reflect JDK 21+ support
- Enables broader compatibility while testing on all recent JDK versions

Author: simbo1905

.github/workflows/maven.yml

@@ -9,14 +9,18 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [ '21', '22', '23', '24' ]
+    name: Build with JDK ${{ matrix.java }}
 
     steps:
     - uses: actions/checkout@v4
 
-    - name: Set up JDK 24
+    - name: Set up JDK ${{ matrix.java }}
       uses: actions/setup-java@v4
       with:
-        java-version: '24'
+        java-version: ${{ matrix.java }}
         distribution: 'oracle'
 
     - name: Cache Maven dependencies

README.md

@@ -1,6 +1,6 @@
-# JSON Experimental - JDK 24 Backport
+# JSON Experimental - JDK 21+ Backport
 
-This repository contains a backport of the experimental JSON API from the [jdk-sandbox project](https://github.com/openjdk/jdk-sandbox) to JDK 24.
+This repository contains a backport of the experimental JSON API from the [jdk-sandbox project](https://github.com/openjdk/jdk-sandbox) to JDK 21 and later.
 
 ## Origin
 
@@ -14,11 +14,11 @@ This is a simplified backport with the following changes from the original:
 - Removed StableValue optimizations
 - Removed value-based class annotations  
 - Basic implementation without performance optimizations
-- Compatible with JDK 24 instead of future JDK versions
+- Compatible with JDK 21+ instead of future JDK versions
 
 ## Building
 
-Requires JDK 24 (Early Access). Build with Maven:
+Requires JDK 21 or later. Build with Maven:
 
 ```bash
 mvn clean compile

pom.xml

@@ -19,8 +19,8 @@
   </licenses>
 
   <properties>
-    <maven.compiler.source>24</maven.compiler.source>
-    <maven.compiler.target>24</maven.compiler.target>
+    <maven.compiler.source>21</maven.compiler.source>
+    <maven.compiler.target>21</maven.compiler.target>
   </properties>
 
   <build>
@@ -30,8 +30,8 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.8.1</version>
         <configuration>
-          <source>24</source>
-          <target>24</target>
+          <source>21</source>
+          <target>21</target>
         </configuration>
       </plugin>
     </plugins>