execute和submit的区别与联系

execute和submit都属于线程池的方法，execute只能提交Runnable类型的任务，而submit既能提交Runnable类型任务也能提交Callable类型任务。

execute会直接抛出任务执行时的异常，submit会吃掉异常，可通过Future的get方法将任务执行时的异常重新抛出。

execute所属顶层接口是Executor,submit所属顶层接口是ExecutorService，实现类ThreadPoolExecutor重写了execute方法,抽象类AbstractExecutorService重写了submit方法。

submit和execute由于参数不同有四种实现形式，如下所示，本文主要研究这四种形式在各自使用场景下的区别和联系

<T> Future<T> submit(Callable<T> task);
<T> Future<T> submit(Runnable task, T result);
Future<?> submit(Runnable task);
void execute(Runnable command);

关于Runnable和Callable任务如果你还存在疑惑，建议你先看看我的上篇文章Runnable和Callable的区别和联系。

测试代码的整体框架如下：

import java.util.concurrent.*;
 
public class TestSubmitAndExecute {
    static ExecutorService executor = Executors.newCachedThreadPool();
 
    public static void main(String[] args) {
        initExecutors();
        /**put test codes here*/
 
 
        /***/
        waitToTerminated();
 
    }
 
 
    private static void initExecutors() {
        if (executor.isTerminated()) {
            executor = Executors.newCachedThreadPool();
        }
    }
 
    private static void waitToTerminated() {
        executor.shutdown();
        while (!executor.isTerminated()) {
        }
    }
 
    /**
     * 测试 submit(Callable<T> task)
     *
     * @param callable
     * @param <T>
     * @return
     */
    public static <T> T testSubmitCallable(Callable callable) {
        Future<T> future = executor.submit(callable);
        T result = null;
        try {
            result = future.get();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        return result;
    }
 
    /**
     * 测试submit(Runnable task, T result)
     *
     * @param runnable
     * @param t
     * @param <T>
     * @return
     */
    public static <T> T testSubmitRunnable(Runnable runnable, T t) {
        Future<T> future = executor.submit(runnable, t);
        T result = null;
        try {
            result = future.get();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        return result;
    }
 
    /**
     * 测试 submit(Runnable task)
     * submit提交Runnable任务会默认返回null
     *
     * @param runnable
     * @return
     */
    public static Object testSubmitRunnable(Runnable runnable) {
        Future<?> future = executor.submit(runnable);
        Object v = null;
        try {
            v = future.get();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        return v;
    }
 
    /**
     * 测试 execute(Runnable command)
     * execute会直接抛出异常，submit只有通过调用Future对象的get方法才能获取异常
     *
     * @param runnable
     */
    public static void testExecuteRunnable(Runnable runnable) {
        executor.execute(runnable);
    }
}

这个测试框架提供了4个静态方法用来测试submit和execute总共包含的四种表现形式，除此之外提供initExecutors用于提前检测线程池是否终止，若终止则初始化，waitToTerminated方法用于关闭线程池，并阻塞到线程池终止为止。

除了测试框架之外提供了4个不同的任务，分别测试Callable和Runnable在抛异常时的表现形式。

class CallableTask implements Callable<Integer> {
    @Override
    public Integer call() throws Exception {
        int sum = 0;
        for (int i = 0; i < 520; i++) {
            sum += i;
        }
        return sum;
    }
}
 
/**
 * 会抛异常的CallableTask
 */
class ExceptionCallableTask implements Callable<Boolean> {
    public Boolean call() throws Exception {
        int num = 1 / 0;
        return false;
    }
}
 
class RunnableTask implements Runnable {
    @Override
    public void run() {
        System.out.println("I am a runnable task");
    }
}
 
/**
 * 会抛异常的RunnableTask
 */
class ExceptionRunableTask implements Runnable {
    @Override
    public void run() {
        int num = 1 / 0;
    }
}

整体结构搭起来，下来就是研究具体差异的时刻了。

1）首先研究Future<?> submit(Runnable task)和void execute(Runnable command)，这两个方法都是执行Runnable类型任务，前者有返回值，但是返回值为null，后者无返回值。

    public static void main(String[] args) {
        initExecutors();
        /**put test codes here*/
        Object object = testSubmitRunnable(new RunnableTask());
        System.out.println(object);
 
        testExecuteRunnable(new RunnableTask());
 
        /***/
        waitToTerminated();
    }

很容易观察控制台输出如下：

I am a runnable task
null
I am a runnable task

可以看出submit执行Runnable类型任务时默认返回值为null。如果我们需要submit在提交Runnable任务可以返回非空，就需要用到submit的另外一个重载的方法：<T> Future<T> submit(Runnable task, T result);

2）submit(Runnable task, T result) 方法可以使submit执行完Runnable任务后返回指定的返回值。

main方法如下：

    public static void main(String[] args) {
        initExecutors();
        /**put test codes here*/
//        Object object = testSubmitRunnable(new RunnableTask());
//        System.out.println(object);
//
//        testExecuteRunnable(new RunnableTask());
 
        Integer i = testSubmitRunnable(new RunnableTask(), 3);
        System.out.println(i);
 
        Boolean bool = testSubmitRunnable(new RunnableTask(), true);
        System.out.println(bool);
 
        String str = testSubmitRunnable(new RunnableTask(), "你好吗");
        System.out.println(str);
 
 
        /***/
        waitToTerminated();
    }

控制台输出：

I am a runnable task
3
I am a runnable task
true
I am a runnable task
你好吗

可以看出我们输入的什么参数，任务执行完毕后就返回什么参数。

3）submit(Callable<T> task)这个方法没什么好说的，用来提交Callable类型任务，返回值由call方法决定。

main方法如下：

    public static void main(String[] args) {
        initExecutors();
        /**put test codes here*/
//        Object object = testSubmitRunnable(new RunnableTask());
//        System.out.println(object);
//
//        testExecuteRunnable(new RunnableTask());
 
//        Integer i = testSubmitRunnable(new RunnableTask(), 3);
//        System.out.println(i);
//
//        Boolean bool = testSubmitRunnable(new RunnableTask(), true);
//        System.out.println(bool);
//
//        String str = testSubmitRunnable(new RunnableTask(), "你好吗");
//        System.out.println(str);
 
        Object o = testSubmitCallable(new CallableTask());
        System.out.println(o);
 
        /***/
        waitToTerminated();
    }

CallableTask的执行逻辑是计算0到520之间的所有整数之和，所以控制台输出：

134940

4）关于execute和submit遭遇异常的表现

execute直接将任务执行时期的异常抛出，main方法和控制台打印分别如下：

    public static void main(String[] args) {
        initExecutors();
        /**put test codes here*/
//        Object object = testSubmitRunnable(new RunnableTask());
//        System.out.println(object);
//
//        testExecuteRunnable(new RunnableTask());
 
//        Integer i = testSubmitRunnable(new RunnableTask(), 3);
//        System.out.println(i);
//
//        Boolean bool = testSubmitRunnable(new RunnableTask(), true);
//        System.out.println(bool);
//
//        String str = testSubmitRunnable(new RunnableTask(), "你好吗");
//        System.out.println(str);
 
//        Object o = testSubmitCallable(new CallableTask());
//        System.out.println(o);
 
        testExecuteRunnable(new ExceptionRunableTask());
 
        /***/
        waitToTerminated();
    }

Exception in thread "pool-1-thread-1" java.lang.ArithmeticException: / by zero
	at ExceptionRunableTask.run(TestRunnableAndCallable.java:38)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

submit比较特殊，如果没有通过Future.get来获取结算结果，则吃掉异常。先将测试方法稍做调整，修改成如下形式：

    /**
     * 测试 submit(Callable<T> task)
     *
     * @param callable
     * @param <T>
     * @return
     */
    public static <T> T testSubmitCallable(Callable callable) {
        Future<T> future = executor.submit(callable);
        T result = null;
        /*
        try {
            result = future.get();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        */
        return result;
    }

当我们在main方法添加如下代码时，控制台其实没有打印任何异常

    public static void main(String[] args) {
        initExecutors();
        /**put test codes here*/
//        Object object = testSubmitRunnable(new RunnableTask());
//        System.out.println(object);
//
//        testExecuteRunnable(new RunnableTask());
 
//        Integer i = testSubmitRunnable(new RunnableTask(), 3);
//        System.out.println(i);
//
//        Boolean bool = testSubmitRunnable(new RunnableTask(), true);
//        System.out.println(bool);
//
//        String str = testSubmitRunnable(new RunnableTask(), "你好吗");
//        System.out.println(str);
 
//        Object o = testSubmitCallable(new CallableTask());
//        System.out.println(o);
 
//        testExecuteRunnable(new ExceptionRunableTask());
 
        testSubmitCallable(new ExceptionCallableTask());
 
        /***/
        waitToTerminated();
    }

如果将testSubmitCallable代码中被注释的部分取消注释，则可以看到异常信息如下：

java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero
	at java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.util.concurrent.FutureTask.get(FutureTask.java:192)
	at TestSubmitAndExecute.testSubmitCallable(TestSubmitAndExecute.java:58)
	at TestSubmitAndExecute.main(TestSubmitAndExecute.java:28)
Caused by: java.lang.ArithmeticException: / by zero
	at ExceptionCallableTask.call(TestRunnableAndCallable.java:20)
	at ExceptionCallableTask.call(TestRunnableAndCallable.java:18)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

关于execute和submit的简单研究到此结束，谢谢观看。

原文地址：https://www.jianshu.com/p/29610984f1dd