java_major_of() {

}

java_env_required=17

java_env_selected=""

if [[ -n "$JAVA_HOME" ]]; then

java_env_current="$(java_major_of "$JAVA_HOME/bin/java")"

# -n first so -ge only ever evaluates a digit string ([[ ]] does arithmetic on its operands).

if [[ -n "$java_env_current" && "$java_env_current" -ge "$java_env_required" ]]; then

java_env_selected="$JAVA_HOME"

else

echo ">>> JAVA_HOME points at Java ${java_env_current:-unknown}, but the build needs >= $java_env_required — looking for another JDK"

fi

if [[ -z "$java_env_selected" ]]; then

for java_env_candidate in \

/usr/lib/jvm/java-17-openjdk-amd64 \

/usr/lib/jvm/java-17-openjdk \

/usr/lib/jvm/java-21-openjdk-amd64 \

/usr/lib/jvm/java-21-openjdk \

"$(/usr/libexec/java_home -v 17 2>/dev/null)" \

"$(/usr/libexec/java_home -v 21 2>/dev/null)"; do

[[ -n "$java_env_candidate" ]] || continue

java_env_candidate_major="$(java_major_of "$java_env_candidate/bin/java")"

if [[ -n "$java_env_candidate_major" && "$java_env_candidate_major" -ge "$java_env_required" ]]; then

java_env_selected="$java_env_candidate"

break

fi

done

if [[ -n "$java_env_selected" ]]; then

export JAVA_HOME="$java_env_selected"

export PATH="$JAVA_HOME/bin:$PATH"

echo ">>> Using JDK $(java_major_of "$JAVA_HOME/bin/java") at $JAVA_HOME"

java_env_path_major="$(java_major_of "$(command -v java 2>/dev/null)")"

echo ">>> WARNING: no JDK >= $java_env_required found (java on PATH is ${java_env_path_major:-missing})."

echo " The build will fail with \"'17' is not a valid choice for '-release'\"."

echo " Install a JDK $java_env_required or set JAVA_HOME to one."