Gradle执行Java类（无需修改build.gradle）

Question

There is simple Eclipse plugin to run Gradle, that just uses command line way to launch gradle.

What is gradle analog for maven compile and run mvn compile exec:java -Dexec.mainClass=example.Example

This way any project with gradle.build could be run.

UPDATE: There was similar question What is the gradle equivalent of maven's exec plugin for running Java apps? asked before, but solution suggested altering every project build.gradle

package runclass;

public class RunClass {
    public static void main(String[] args) {
        System.out.println("app is running!");
    }
}

Then executing gradle run -DmainClass=runclass.RunClass

:run FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':run'.
> No main class specified   

Answer 1

There is no direct equivalent to mvn exec:java in gradle, you need to either apply the application plugin or have a JavaExec task.

application plugin

Activate the plugin:

plugins {
    id 'application'
    ...
}

Configure it as follows:

application {
    mainClassName = project.hasProperty("mainClass") ? project.getProperty("mainClass") : "NULL"
}

On the command line, write

$ gradle -PmainClass=Boo run

JavaExec task

Define a task, let's say execute :

task execute(type:JavaExec) {
   main = project.hasProperty("mainClass") ? getProperty("mainClass") : "NULL"
   classpath = sourceSets.main.runtimeClasspath
}

To run, write gradle -PmainClass=Boo execute . You get

$ gradle -PmainClass=Boo execute
:compileJava
:compileGroovy UP-TO-DATE
:processResources UP-TO-DATE
:classes
:execute
I am BOO!

mainClass is a property passed in dynamically at command line. classpath is set to pickup the latest classes.

---

If you do not pass in the mainClass property, both of the approaches fail as expected.

$ gradle execute

FAILURE: Build failed with an exception.

* Where:
Build file 'xxxx/build.gradle' line: 4

* What went wrong:
A problem occurred evaluating root project 'Foo'.
> Could not find property 'mainClass' on task ':execute'.

Answer 2

You just need to use the Gradle Application plugin :

apply plugin:'application'
mainClassName = "org.gradle.sample.Main"

And then simply gradle run .

As Teresa points out, you can also configure mainClassName as a system property and run with a command line argument.

Answer 3

Expanding on First Zero's answer, I'm guess you want something where you can also run gradle build without errors.

Both gradle build and gradle -PmainClass=foo runApp work with this:

task runApp(type:JavaExec) {
    classpath = sourceSets.main.runtimeClasspath

    main = project.hasProperty("mainClass") ? project.getProperty("mainClass") : "package.MyDefaultMain"
}

where you set your default main class.

Answer 4

You can parameterise it and pass gradle clean build -Pprokey=goodbye

task choiceMyMainClass(type: JavaExec) {
     group = "Execution"
    description = "Run Option main class with JavaExecTask"
    classpath = sourceSets.main.runtimeClasspath

    if (project.hasProperty('prokey')){
        if (prokey == 'hello'){
            main = 'com.sam.home.HelloWorld'
        } 
        else if (prokey == 'goodbye'){
            main = 'com.sam.home.GoodBye'
        }
    } else {
            println 'Invalid value is enterrd';

       // println 'Invalid value is enterrd'+ project.prokey;
    }