JarExec task - supporting execution of Jars (i.e. java -jar). Place in buildSrc/src/main/java/org/gradle/api/tasks/JarExec

build.gradle

class JarExec extends JavaExec {
  private String jar;

  public void setJar(String jar) {
    this.jar = jar;
  }
  public String getJar() {
    return this.jar;
  }
  public void jar(String jar) {
    this.jar = jar;
  }

  @TaskAction
  public void exec() {
    if(this.jar == null) {
       throw new RuntimeException("Jar not specified");
    }

    this.setMain('-jar');
    
    List<String> args = this.getArgs();
    args.add(0,this.jar);
    this.setArgs(args);

    super.exec();
  }

  public String getMain(){
    throw new MissingMethodException("getMain", JarExec.class);
  }

  public JavaExec setMain(String main){
    throw new MissingMethodException("setMain", JarExec.class, main);
  }

  public JavaExecSpec main(String main){
    throw new MissingMethodException("main", JarExec.class, main);
  }
}

task run(type: JarExec) {
   jar 'build/libs/simplest-proj-1.0-SNAPSHOT-fat.jar'
}

JarExec.java

/*
 * Copyright 2011 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.gradle.api.tasks;

import org.gradle.api.file.FileCollection;
import org.gradle.api.internal.ConventionTask;
import org.gradle.api.internal.file.FileResolver;
import org.gradle.api.internal.tasks.options.Option;
import org.gradle.process.JavaExecSpec;
import org.gradle.process.JavaForkOptions;
import org.gradle.process.ProcessForkOptions;
import org.gradle.process.internal.DefaultJavaExecAction;
import org.gradle.process.internal.JavaExecAction;

import javax.inject.Inject;
import java.io.File;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.List;
import java.util.Map;

/**
 * Executes a Java application in a child process.
 * <p>
 * The process can be started in debug mode (see {@link #getDebug()}) in an ad-hoc manner by supplying the `--debug-jvm` switch when invoking the build.
 * <pre>
 * gradle someJavaExecTask --debug-jvm
 * </pre>
 */
public class JarExec extends ConventionTask {
    private JavaExecAction javaExecHandleBuilder;
    private String jar = null;

    public JarExec() {
        javaExecHandleBuilder = new DefaultJavaExecAction(getFileResolver());
    }

    @Inject
    protected FileResolver getFileResolver() {
        throw new UnsupportedOperationException();
    }

    @TaskAction
    public void exec() {
	    if(this.jar == null) {
	       throw new RuntimeException("Jar not specified");
	    }

	    // tell builder to use -jar as main
	    javaExecHandleBuilder.setMain("-jar");

        setJvmArgs(getJvmArgs()); // from JavaExec. Convention mapping.
	
			// put jar at beginning after -jar
	    List<String> args = javaExecHandleBuilder.getArgs();
	    args.add(0,this.jar);
	    javaExecHandleBuilder.setArgs(args);

        javaExecHandleBuilder.execute();
    }

    public void setJar(String jar) {
        this.jar = jar;
    }

    public String getJar() {
        return this.jar;
    }

    public void jar(String jar) {
        this.jar = jar;
    }

    /**
     * {@inheritDoc}
     */
    public List<String> getAllJvmArgs() {
        return javaExecHandleBuilder.getAllJvmArgs();
    }

    /**
     * {@inheritDoc}
     */
    public void setAllJvmArgs(Iterable<?> arguments) {
        javaExecHandleBuilder.setAllJvmArgs(arguments);
    }

    /**
     * {@inheritDoc}
     */
    public List<String> getJvmArgs() {
        return javaExecHandleBuilder.getJvmArgs();
    }

    /**
     * {@inheritDoc}
     */
    public void setJvmArgs(Iterable<?> arguments) {
        javaExecHandleBuilder.setJvmArgs(arguments);
    }

    /**
     * {@inheritDoc}
     */
    public JarExec jvmArgs(Iterable<?> arguments) {
        javaExecHandleBuilder.jvmArgs(arguments);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec jvmArgs(Object... arguments) {
        javaExecHandleBuilder.jvmArgs(arguments);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public Map<String, Object> getSystemProperties() {
        return javaExecHandleBuilder.getSystemProperties();
    }

    /**
     * {@inheritDoc}
     */
    public void setSystemProperties(Map<String, ?> properties) {
        javaExecHandleBuilder.setSystemProperties(properties);
    }

    /**
     * {@inheritDoc}
     */
    public JarExec systemProperties(Map<String, ?> properties) {
        javaExecHandleBuilder.systemProperties(properties);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec systemProperty(String name, Object value) {
        javaExecHandleBuilder.systemProperty(name, value);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    @InputFiles
    public FileCollection getBootstrapClasspath() {
        return javaExecHandleBuilder.getBootstrapClasspath();
    }

    /**
     * {@inheritDoc}
     */
    public void setBootstrapClasspath(FileCollection classpath) {
        javaExecHandleBuilder.setBootstrapClasspath(classpath);
    }

    /**
     * {@inheritDoc}
     */
    public JarExec bootstrapClasspath(Object... classpath) {
        javaExecHandleBuilder.bootstrapClasspath(classpath);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public String getMinHeapSize() {
        return javaExecHandleBuilder.getMinHeapSize();
    }

    /**
     * {@inheritDoc}
     */
    public void setMinHeapSize(String heapSize) {
        javaExecHandleBuilder.setMinHeapSize(heapSize);
    }

    /**
     * {@inheritDoc}
     */
    public String getDefaultCharacterEncoding() {
        return javaExecHandleBuilder.getDefaultCharacterEncoding();
    }

    /**
     * {@inheritDoc}
     */
    public void setDefaultCharacterEncoding(String defaultCharacterEncoding) {
        javaExecHandleBuilder.setDefaultCharacterEncoding(defaultCharacterEncoding);
    }

    /**
     * {@inheritDoc}
     */
    public String getMaxHeapSize() {
        return javaExecHandleBuilder.getMaxHeapSize();
    }

    /**
     * {@inheritDoc}
     */
    public void setMaxHeapSize(String heapSize) {
        javaExecHandleBuilder.setMaxHeapSize(heapSize);
    }

    /**
     * {@inheritDoc}
     */
    public boolean getEnableAssertions() {
        return javaExecHandleBuilder.getEnableAssertions();
    }

    /**
     * {@inheritDoc}
     */
    public void setEnableAssertions(boolean enabled) {
        javaExecHandleBuilder.setEnableAssertions(enabled);
    }

    /**
     * {@inheritDoc}
     */
    public boolean getDebug() {
        return javaExecHandleBuilder.getDebug();
    }

    /**
     * {@inheritDoc}
     */
    @Option(option = "debug-jvm", description = "Enable debugging for the process. The process is started suspended and listening on port 5005. [INCUBATING]")
    public void setDebug(boolean enabled) {
        javaExecHandleBuilder.setDebug(enabled);
    }

    /**
     * {@inheritDoc}
     */
    public List<String> getArgs() {
        return javaExecHandleBuilder.getArgs();
    }

    /**
     * {@inheritDoc}
     */
    public JarExec setArgs(Iterable<?> applicationArgs) {
        javaExecHandleBuilder.setArgs(applicationArgs);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec args(Object... args) {
        javaExecHandleBuilder.args(args);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec args(Iterable<?> args) {
        javaExecHandleBuilder.args(args);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec setClasspath(FileCollection classpath) {
        javaExecHandleBuilder.setClasspath(classpath);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec classpath(Object... paths) {
        javaExecHandleBuilder.classpath(paths);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    @InputFiles
    public FileCollection getClasspath() {
        return javaExecHandleBuilder.getClasspath();
    }

    /**
     * {@inheritDoc}
     */
    public JarExec copyTo(JavaForkOptions options) {
        javaExecHandleBuilder.copyTo(options);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public String getExecutable() {
        return javaExecHandleBuilder.getExecutable();
    }

    /**
     * {@inheritDoc}
     */
    public void setExecutable(Object executable) {
        javaExecHandleBuilder.setExecutable(executable);
    }

    /**
     * {@inheritDoc}
     */
    public JarExec executable(Object executable) {
        javaExecHandleBuilder.executable(executable);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public File getWorkingDir() {
        return javaExecHandleBuilder.getWorkingDir();
    }

    /**
     * {@inheritDoc}
     */
    public void setWorkingDir(Object dir) {
        javaExecHandleBuilder.setWorkingDir(dir);
    }

    /**
     * {@inheritDoc}
     */
    public JarExec workingDir(Object dir) {
        javaExecHandleBuilder.workingDir(dir);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public Map<String, Object> getEnvironment() {
        return javaExecHandleBuilder.getEnvironment();
    }

    /**
     * {@inheritDoc}
     */
    public void setEnvironment(Map<String, ?> environmentVariables) {
        javaExecHandleBuilder.setEnvironment(environmentVariables);
    }

    /**
     * {@inheritDoc}
     */
    public JarExec environment(String name, Object value) {
        javaExecHandleBuilder.environment(name, value);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec environment(Map<String, ?> environmentVariables) {
        javaExecHandleBuilder.environment(environmentVariables);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec copyTo(ProcessForkOptions target) {
        javaExecHandleBuilder.copyTo(target);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public JarExec setStandardInput(InputStream inputStream) {
        javaExecHandleBuilder.setStandardInput(inputStream);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public InputStream getStandardInput() {
        return javaExecHandleBuilder.getStandardInput();
    }

    /**
     * {@inheritDoc}
     */
    public JarExec setStandardOutput(OutputStream outputStream) {
        javaExecHandleBuilder.setStandardOutput(outputStream);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public OutputStream getStandardOutput() {
        return javaExecHandleBuilder.getStandardOutput();
    }

    /**
     * {@inheritDoc}
     */
    public JarExec setErrorOutput(OutputStream outputStream) {
        javaExecHandleBuilder.setErrorOutput(outputStream);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public OutputStream getErrorOutput() {
        return javaExecHandleBuilder.getErrorOutput();
    }

    /**
     * {@inheritDoc}
     */
    public JarExec setIgnoreExitValue(boolean ignoreExitValue) {
        javaExecHandleBuilder.setIgnoreExitValue(ignoreExitValue);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public boolean isIgnoreExitValue() {
        return javaExecHandleBuilder.isIgnoreExitValue();
    }

    /**
     * {@inheritDoc}
     */
    public List<String> getCommandLine() {
        return javaExecHandleBuilder.getCommandLine();
    }
}