Problems passing system properties and parameters when running Java class via Gradle

Figured it out. The main issue is that when Gradle forks a new Java process, it does not automatically pass the environment variable values along to the new environment. One has to explicitly pass these variables via the systemProperties property of the task or plugin.

The other issue was understanding how to pass command-line args; these are via the args property on the task or plugin. As with the Maven exec-maven-plugin, they should be passed in on the command line via yet another system property, as a space-delimited list that then needs to be split() before setting args, which accepts List objects. I’ve named the property exec.args, which is the old Maven name.

It seems both the javaExec and application plugin approach are valid. One might favor the application plugin approach if one wants to use some of its other features (automatically putting together a distribution, etc.)

Here are the solutions:

JavaExec Approach

Command Line:

gradle execute -Dmyvariable=myvalue -Dexec.args="arg1 arg2 arg3"

build.gradle:

task execute (type:JavaExec) {

    main = "com.myCompany.MyMain"
    classpath = sourceSets.main.runtimeClasspath 

    /* Can pass all the properties: */
    systemProperties System.getProperties()

    /* Or just each by name: */
    systemProperty "myvariable", System.getProperty("myvariable")

    /* Need to split the space-delimited value in the exec.args */
    args System.getProperty("exec.args", "").split()    
}

Application Plugin Approach

Command Line:

gradle run -Dmyvariable=myvalue -Dexec.args="arg1 arg2 arg3"

build.gradle:

apply plugin: 'application'
mainClassName = "com.mycompany.MyMain"
run {    
    /* Can pass all the properties: */
    systemProperties System.getProperties()

    /* Or just each by name: */
    systemProperty "myvariable", System.getProperty("myvariable")

    /* Need to split the space-delimited value in the exec.args */
    args System.getProperty("exec.args", "").split()    
}