jdk_switcher.sh

#!/usr/bin/env bash

if uname -a | grep x86_64 >/dev/null; then
    ARCH_SUFFIX=amd64
else
    ARCH_SUFFIX=i386
fi

: "${JDK_SWITCHER_DEFAULT:=openjdk8}"
: "${UJA:=update-java-alternatives}"

OPENJDK6_UJA_ALIAS="java-1.6.0-openjdk"
OPENJDK6_JAVA_HOME="/usr/lib/jvm/java-6-openjdk"
if [[ -d "/usr/lib/jvm/java-6-openjdk-${ARCH_SUFFIX}" ]]; then
    OPENJDK6_UJA_ALIAS="java-1.6.0-openjdk-${ARCH_SUFFIX}"
    OPENJDK6_JAVA_HOME="/usr/lib/jvm/java-6-openjdk-${ARCH_SUFFIX}"
fi

OPENJDK7_UJA_ALIAS="java-1.7.0-openjdk"
OPENJDK7_JAVA_HOME="/usr/lib/jvm/java-7-openjdk"
if [[ -d "/usr/lib/jvm/java-7-openjdk-${ARCH_SUFFIX}" ]]; then
    OPENJDK7_UJA_ALIAS="java-1.7.0-openjdk-${ARCH_SUFFIX}"
    OPENJDK7_JAVA_HOME="/usr/lib/jvm/java-7-openjdk-${ARCH_SUFFIX}"
fi

OPENJDK8_UJA_ALIAS="java-1.8.0-openjdk"
OPENJDK8_JAVA_HOME="/usr/lib/jvm/java-8-openjdk"
if [[ -d "/usr/lib/jvm/java-8-openjdk-${ARCH_SUFFIX}" ]]; then
    OPENJDK8_UJA_ALIAS="java-1.8.0-openjdk-${ARCH_SUFFIX}"
    OPENJDK8_JAVA_HOME="/usr/lib/jvm/java-8-openjdk-${ARCH_SUFFIX}"
fi

ORACLEJDK7_UJA_ALIAS="java-7-oracle"
ORACLEJDK7_JAVA_HOME="/usr/lib/jvm/java-7-oracle"
if [[ -d "/usr/lib/jvm/java-7-oracle-${ARCH_SUFFIX}" ]]; then
    ORACLEJDK7_UJA_ALIAS="java-7-oracle-${ARCH_SUFFIX}"
    ORACLEJDK7_JAVA_HOME="/usr/lib/jvm/java-7-oracle-${ARCH_SUFFIX}"
fi

ORACLEJDK8_UJA_ALIAS="java-8-oracle"
ORACLEJDK8_JAVA_HOME="/usr/lib/jvm/java-8-oracle"
if [[ -d "/usr/lib/jvm/java-8-oracle-${ARCH_SUFFIX}" ]]; then
    ORACLEJDK8_UJA_ALIAS="java-8-oracle-${ARCH_SUFFIX}"
    ORACLEJDK8_JAVA_HOME="/usr/lib/jvm/java-8-oracle-${ARCH_SUFFIX}"
fi

ORACLEJDK9_UJA_ALIAS="java-9-oracle"
ORACLEJDK9_JAVA_HOME="/usr/lib/jvm/java-9-oracle"
if [[ -d "/usr/lib/jvm/java-9-oracle-${ARCH_SUFFIX}" ]]; then
    ORACLEJDK9_UJA_ALIAS="java-9-oracle-${ARCH_SUFFIX}"
    ORACLEJDK9_JAVA_HOME="/usr/lib/jvm/java-9-oracle-${ARCH_SUFFIX}"
fi

for config_file in /etc/default/jdk-switcher "${HOME}/.jdk_switcherrc" "${JDK_SWITCHER_CONFIG}"; do
    if [[ -f "${config_file}" ]]; then
        # shellcheck source=/dev/null
        source "${config_file}"
    fi
done

switch_to_openjdk6() {
    echo "Switching to OpenJDK6 ($OPENJDK6_UJA_ALIAS), JAVA_HOME will be set to $OPENJDK6_JAVA_HOME"
    sudo "${UJA}" --set "$OPENJDK6_UJA_ALIAS"
    export JAVA_HOME="$OPENJDK6_JAVA_HOME"
}

switch_to_openjdk7() {
    echo "Switching to OpenJDK7 ($OPENJDK7_UJA_ALIAS), JAVA_HOME will be set to $OPENJDK7_JAVA_HOME"
    sudo "${UJA}" --set "$OPENJDK7_UJA_ALIAS"
    export JAVA_HOME="$OPENJDK7_JAVA_HOME"
}

switch_to_openjdk8() {
    echo "Switching to OpenJDK8 ($OPENJDK8_UJA_ALIAS), JAVA_HOME will be set to $OPENJDK8_JAVA_HOME"
    sudo "${UJA}" --set "$OPENJDK8_UJA_ALIAS"
    export JAVA_HOME="$OPENJDK8_JAVA_HOME"
}

switch_to_oraclejdk7() {
    echo "Switching to Oracle JDK7 ($ORACLEJDK7_UJA_ALIAS), JAVA_HOME will be set to $ORACLEJDK7_JAVA_HOME"
    sudo "${UJA}" --set "$ORACLEJDK7_UJA_ALIAS"
    export JAVA_HOME="$ORACLEJDK7_JAVA_HOME"
}

switch_to_oraclejdk8() {
    echo "Switching to Oracle JDK8 ($ORACLEJDK8_UJA_ALIAS), JAVA_HOME will be set to $ORACLEJDK8_JAVA_HOME"
    sudo "${UJA}" --set "$ORACLEJDK8_UJA_ALIAS"
    export JAVA_HOME="$ORACLEJDK8_JAVA_HOME"
}

switch_to_oraclejdk9() {
    echo "Switching to Oracle JDK9 ($ORACLEJDK9_UJA_ALIAS), JAVA_HOME will be set to $ORACLEJDK9_JAVA_HOME"
    sudo "${UJA}" --set "$ORACLEJDK9_UJA_ALIAS"
    export JAVA_HOME="$ORACLEJDK9_JAVA_HOME"
}

print_home_of_openjdk6() {
    echo "$OPENJDK6_JAVA_HOME"
}

print_home_of_openjdk7() {
    echo "$OPENJDK7_JAVA_HOME"
}

print_home_of_openjdk8() {
    echo "$OPENJDK8_JAVA_HOME"
}

print_home_of_oraclejdk7() {
    echo "$ORACLEJDK7_JAVA_HOME"
}

print_home_of_oraclejdk8() {
    echo "$ORACLEJDK8_JAVA_HOME"
}

print_home_of_oraclejdk9() {
    echo "$ORACLEJDK9_JAVA_HOME"
}

warn_sunjdk6_eol() {
    echo "Sun/Oracle JDK 6 is EOL since November 2012, and is no longer supported. Please consider upgrading..." >&2
}

warn_jdk_not_known() {
    echo "Sorry, but JDK '$1' is not known." >&2
}

warn_gcj_user() {
    echo "We do not support GCJ. I mean, come on. Are you Richard Stallman?" >&2
}

switch_jdk() {
    case "${1:-default}" in
        *gcj*)
            warn_gcj_user
            false
            ;;
        openjdk6 | openjdk1.6 | openjdk1.6.0 | jdk6 | 1.6.0 | 1.6 | 6.0)
            switch_to_openjdk6
            ;;
        openjdk7 | jdk7 | 1.7.0 | 1.7 | 7.0)
            switch_to_openjdk7
            ;;
        openjdk8 | jdk8 | 1.8.0 | 1.8 | 8.0)
            switch_to_openjdk8
            ;;
        oraclejdk6 | oraclejdk1.6 | oraclejdk1.6.0 | oracle6 | oracle1.6.0 | oracle6.0 | sunjdk6 | sun6)
            warn_sunjdk6_eol
            false
            ;;
        oraclejdk7 | oraclejdk1.7 | oraclejdk1.7.0 | oracle7 | oracle1.7.0 | oracle7.0 | oracle | sunjdk7 | sun7 | sun)
            switch_to_oraclejdk7
            ;;
        oraclejdk8 | oraclejdk1.8 | oraclejdk1.8.0 | oracle8 | oracle1.8.0 | oracle8.0)
            switch_to_oraclejdk8
            ;;
        oraclejdk9 | oraclejdk1.9 | oraclejdk1.9.0 | oracle9 | oracle1.9.0 | oracle9.0)
            switch_to_oraclejdk9
            ;;
        default)
            "switch_to_${JDK_SWITCHER_DEFAULT}"
            ;;
        *)
            warn_jdk_not_known "$1"
            false
            ;;
    esac
}

print_java_home() {
    typeset JDK
    JDK="$1"

    case "$JDK" in
        *gcj*)
            warn_gcj_user
            ;;
        openjdk6 | openjdk1.6 | openjdk1.6.0 | jdk6 | 1.6.0 | 1.6 | 6.0)
            print_home_of_openjdk6
            ;;
        openjdk7 | jdk7 | 1.7.0 | 1.7 | 7.0)
            print_home_of_openjdk7
            ;;
        openjdk8 | jdk8 | 1.8.0 | 1.8 | 8.0)
            print_home_of_openjdk8
            ;;
        oraclejdk6 | oraclejdk1.6 | oraclejdk1.6.0 | oracle6 | oracle1.6.0 | oracle6.0 | sunjdk6 | sun6)
            warn_sunjdk6_eol
            ;;
        oraclejdk7 | oraclejdk1.7 | oraclejdk1.7.0 | oracle7 | oracle1.7.0 | oracle7.0 | oracle | sunjdk7 | sun7 | sun)
            print_home_of_oraclejdk7
            ;;
        oraclejdk8 | oraclejdk1.8 | oraclejdk1.8.0 | oracle8 | oracle1.8.0 | oracle8.0)
            print_home_of_oraclejdk8
            ;;
        oraclejdk9 | oraclejdk1.9 | oraclejdk1.9.0 | oracle9 | oracle1.9.0 | oracle9.0)
            print_home_of_oraclejdk9
            ;;
        default)
            "print_home_of_${JDK_SWITCHER_DEFAULT}"
            ;;
        *)
            warn_jdk_not_known "$JDK"
            ;;
    esac
}

jdk_switcher() {
    typeset COMMAND JDK
    COMMAND="$1"
    JDK="$2"

    case "$COMMAND" in
        use)
            switch_jdk "$JDK"
            ;;
        home)
            print_java_home "$JDK"
            ;;
        *)
            echo "Usage: jdk_switcher {use|home} [ JDK version ]" >&2
            false
            ;;
    esac

    return $?
}