Gradle to execute Java class (without modifying build.gradle)

问题

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

回答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") ? 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'.

回答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.

回答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.

来源：https://stackoverflow.com/questions/21358466/gradle-to-execute-java-class-without-modifying-build-gradle

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java

gradle

execution