ZBlog

I love to use bash shell terminal. It’s a much more powerful terminal to do everyday tasks. Even in Windows, I can get most of what I need using Cygwin. Unfortunately Java executable are native to OS only, and for Windows, it would still work under Cygwin, but all the file system paths are still native. Java can understand the mixed-path though, and it has made somewhat easier than the Windows native backward slash path like typing. This means we can define JAVA_HOME variable using mixed path mode. In Cygwin, I define my .bashrc like this:

export JAVA_HOME=C:/Users/zemian/apps/jdk-8u161
PATH=$HOME/apps/jdk-8u161/bin:$PATH

I sometimes work with different version of JDK for various application testing. In this case, I need a way to quicly switch JDK version in my shell env. To make it easier, I have installed all of my JDK in a $HOME/apps directory, and created symbolic links to each JDKs like this:

    cd $HOME/apps
    ls -ld jdk*

    drwx------+ 1 zemian staff 0 Mar 24 16:58 jdk-8u161
    drwx------+ 1 zemian staff 0 Mar 24 10:57 jdk-9.0.4
    drwx------+ 1 zemian staff 0 Mar 24 10:48 jdk-10

    lrwxrwxrwx  1 zemian staff 9 Mar 24 16:55 jdk8 -> jdk-8u161
    lrwxrwxrwx  1 zemian staff 9 Mar 24 11:02 jdk9 -> jdk-9.0.4
    lrwxrwxrwx  1 zemian staff 6 Mar 24 11:00 jdk10 -> jdk-10

Now that each JDK has a nice consistent version number in path, then I create a shell function like this to switch between them:

    # Switching Multiple JDK
    switchjava() {
            JDK="jdk$1"
            if [[ ! -d $APPS_DIR/$JDK ]]; then
                    echo "ERROR: JDK path not found: $APPS_DIR/$JDK"
                    return
            fi
            export JAVA_HOME=`cygpath -wm $APPS_DIR/$JDK`
            export PATH=$APPS_DIR/$JDK/bin:$PATH

            # Verifying java
            echo "Switched JAVA_HOME to $JAVA_HOME"
            echo "Java Path:"
            which java
            echo "Java Version:"
            java -version
    }

To put it in use, it looks like this:

    $ switchjava 9
    Switched JAVA_HOME to C:/Users/zemian/apps/jdk-9.0.4
    Java Path:
    /home/zemian/apps/jdk9/bin/java
    Java Version:
    openjdk version "9.0.4"
    OpenJDK Runtime Environment (build 9.0.4+11)
    OpenJDK 64-Bit Server VM (build 9.0.4+11, mixed mode)

    $ switchjava 8
    Switched JAVA_HOME to C:/Users/zemian/apps/jdk-8u161
    Java Path:
    /home/zemian/apps/jdk8/bin/java
    Java Version:
    java version "1.8.0_161"
    Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
    Java HotSpot(TM) 64-Bit Server VM (build 25.161-b12, mixed mode)

Switching Different JDK in Cygwin