How to pass multiple parameters in command line when running gradle task?

JavaExec may be the way to go. Just declare a task and pass project parameters to java app:

task myExecTask(type: JavaExec) {
   classpath = sourceSets.main.runtimeClasspath
   main = 'com.project.MyApplicationMainClass' 
   args project.getProperty('userName') + ' ' + project.getProperty('password');
}

To run it, simply write gradle myExecTask -PuserName=john -Ppassword=secret