Add workflow file for Java example (#247)

Author: ava-cassiopeia

.github/workflows/java_build_and_test.yml

@@ -0,0 +1,34 @@
+name: Java sample build and test
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'a2a_agents/java/**'
+  pull_request:
+    paths:
+      - 'a2a_agents/java/**'
+
+jobs:
+  build-and-test:
+    name: Build and test Java agent sample
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Set up JDK
+        uses: actions/setup-java@v3
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+
+      - name: Build with Maven
+        working-directory: a2a_agents/java
+        run: mvn clean install
+
+      - name: Run Tests
+        working-directory: a2a_agents/java
+        run: mvn test

a2a_agents/java/.gitignore

@@ -0,0 +1,2 @@
+# Automatic build file output from some IDEs and editors
+target

a2a_agents/java/pom.xml

@@ -9,8 +9,8 @@
     <version>0.1.0-SNAPSHOT</version>
 
     <properties>
-        <maven.compiler.source>17</maven.compiler.source>
-        <maven.compiler.target>17</maven.compiler.target>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <a2a.sdk.version>0.3.3.Final</a2a.sdk.version>
         <junit.version>5.10.2</junit.version>