GradleでJavaアプリを実行する最小構成サンプル ref: http://qiita.com/kazurof/items/d5b00f7baf2b1699257d

build.gradle

apply plugin: 'java'

repositories {
  jcenter()
}

dependencies {
  compile 'org.apache.commons:commons-lang3:3.4'
}

task nantoka(type: JavaExec) {
  main = "org.example.Nantoka"
  classpath = sourceSets.main.runtimeClasspath
  args('apple', 'banana', 'cherry')
  args 'durian'
}

// gradle -Ddousita.param=kousita kantoka
task kantoka(type: JavaExec) {
  main = "org.example.Kantoka"
  classpath = sourceSets.main.runtimeClasspath
  args(System.properties['dousita.param'] ?: "default")
}

file3.txt

│  build.gradle
└─src
    └─main
        └─java
            └─org
                └─example
                        Kantoka.java
                        Nantoka.java

Kantoka.java

package org.example;

import org.apache.commons.lang3.SystemUtils;

import java.util.Arrays;

public class Kantoka {
  public static void main(String[] args) {
    System.out.println("This is Kantoka");
    System.out.println(args.length);
    Arrays.stream(args).forEach(System.out::println);
    System.out.println(SystemUtils.JAVA_VERSION);
    Nantoka.doNantoka();
  }

  static void doKantoka() {
    System.out.println("i am Kantoka");
  }
}

Nantoka.java

package org.example;

import java.util.Arrays;

public class Nantoka {
  public static void main(String[] args) {
    System.out.println("This is Nantoka");
    System.out.println(args.length);
    Arrays.stream(args).forEach(System.out::println);
    Kantoka.doKantoka();
  }

  static void doNantoka() {
    System.out.println("i am Nantoka");
  }
}