Java线程池中submit() 和 execute()方法有什么区别

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一. 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类型任务也能提交哦啊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，可以通过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，建议你先看看我的另一篇文章Runnable和Callable的区别和联系。

1、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> {@Overridepublic 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 {@Overridepublic void run() {System.out.println("I am a runnable task");}
}/*** 会抛异常的RunnableTask*/
class ExceptionRunableTask implements Runnable {@Overridepublic 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。

2、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： Future submit(Runnable task, T result);

3、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。

4、submit(Callable 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

5、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 zeroat 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：**```bash
java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zeroat 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 zeroat 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。