gradle: change default port from 5005

Question

I want to debug some JVM instances that are running at the same time. I know that I can run gradle using --debug-jvm so that the JVM will wait until I start the IDE debugger so that it connects to the JVM but it uses port 5005 by default. That's fine for debugging one instance of JVM... but if I want to debug more than one instance, I'll need to define a different port from 5005. How can I achieve this with gradle?

Answer 1

In my case I wanted to debug a specific file, so I included the following code in build.gradle:

task execFile(type: JavaExec) {
    main = mainClass

    classpath = sourceSets.main.runtimeClasspath
    
    if (System.getProperty('debug', 'false') == 'true') {
        jvmArgs "-Xdebug", "-agentlib:jdwp=transport=dt_socket,address=8787,server=y,suspend=y"
    }

    systemProperties System.getProperties()
}

and I can run with:

gradle execFile -PmainClass=com.MyClass -Dmyprop=somevalue -Ddebug=true

The custom execFile task receives:

• -PmainClass=com.MyClass: the class with the main method I want to execute (in the script, main = mainClass)
• -Dmyprop=somevalue: a property whose value be retrieved in the application calling System.getProperty("myprop") (in the script, systemProperties System.getProperties() was needed for that)
• -Ddebug=true: a flag to enable debugging on port 8787 (in the script, see the if condition, and also address=8787, but the port could be changed, and this flag name also could be changed). Using suspend=y the execution is suspended until the debugger is attached to the port (if you don't want this behaviour, you could use suspend=n)

For your use case, you could try to apply the logic behind the line jvmArgs ... to your specific task (or use tasks.withType(JavaExec) { ... } to apply to all tasks of this type).

Using this solution, don't use the --debug-jvm option because you may receive an error about the property jdwp being defined twice.

Update (2020-08-10)

To make sure that the code runs only when I execute the task execFile explicitly (so as to not run when I just build gradle, for example), I changed the code to:

task execFile {
    dependsOn 'build'

    doLast {
        tasks.create('execFileJavaExec', JavaExec) {
            main = mainClass
            classpath = sourceSets.main.runtimeClasspath

            if (System.getProperty('debug', 'false') == 'true') {
                jvmArgs "-Xdebug", "-agentlib:jdwp=transport=dt_socket,address=*:8787,server=y,suspend=y"
            }

            systemProperties System.getProperties()
        }.exec()
    }
}

See more at: Run gradle task only when called specifically

Answer 2

You could modify GRADLE_OPTS environment variable and add standard Java debugger syntax e.g. to use port 8888:

-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8888