feat(java): make Java 21 default

Author: Greelan

java/lts/Dockerfile

@@ -7,6 +7,8 @@ LABEL       org.opencontainers.image.licenses=MIT
 
 ENV         DEBIAN_FRONTEND="noninteractive"
 
+ARG         TARGETARCH
+
 # Install required packages and Temurin Java LTS versions
 RUN         set -eux; \
             apt-get update; \
@@ -19,5 +21,16 @@ RUN         set -eux; \
             apt-get update; \
             apt-get install -o APT::Keep-Downloaded-Packages="false" -y \
                 temurin-8-jdk temurin-11-jdk temurin-17-jdk temurin-21-jdk temurin-25-jdk; \
+            # Set Java 21 as the default version
+            case "${TARGETARCH}" in \
+                amd64) \
+                    update-alternatives --set java /usr/lib/jvm/temurin-21-jdk-amd64/bin/java; \
+                    update-alternatives --set javac /usr/lib/jvm/temurin-21-jdk-amd64/bin/javac; \
+                ;; \
+                arm64) \
+                    update-alternatives --set java /usr/lib/jvm/temurin-21-jdk-arm64/bin/java; \
+                    update-alternatives --set javac /usr/lib/jvm/temurin-21-jdk-arm64/bin/javac; \
+                ;; \
+            esac; \
             apt-get clean; \
             rm -rf /var/lib/apt/lists/*