一、概述

execute和submit都是线程池中执行任务的方法。

execute是Executor接口中的方法

public interface Executor {

    void execute(Runnable command);
}

submit是ExecuteService接口中的方法。

public interface ExecutorService extends Executor {

    <T> Future<T> submit(Callable<T> task);
  
    <T> Future<T> submit(Runnable task, T result);
   
    Future<?> submit(Runnable task);
}

通过源码可以看出execute方法无返回值，参数为Runnable对象。
submit方法有三个重载方法，都有Future类型的返回值，参数可以是Runnable对象，Callable对象，Runnable对象和一个其他类型的对象。

那么在执行过程中有异常抛出会怎么样呢，先说答案，execute方法会直接抛出异常，submit方法不会抛出异常，只有在通过Future的get方法获取结果的时候才会抛出异常，下面进行测试：

public class ExecutorTest1 {

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        ExecutorTest1 test1 = new ExecutorTest1();
        executorService.execute(() -> test1.say("execute方法"));
        executorService.submit(() -> test1.say("submit方法"));
        executorService.shutdown();
    }

    private void say(String msg){
        System.out.println(msg);
        throw new RuntimeException("抛出了异常："+ msg);
    }
}

执行结果如下：

可见execute方法直接抛出了异常，submit方法只打印了参数没有抛出异常，下面测试使用Future的get方法获取结果：

public class ExecutorTest1 {

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        ExecutorTest1 test1 = new ExecutorTest1();
        executorService.execute(() -> test1.say("execute方法"));
        Future<?> submitFuture = executorService.submit(() -> test1.say("submit方法"));
        try {
            Object o = submitFuture.get();
            System.out.println("这是submit的返回值："+o);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        executorService.shutdown();
    }

    private void say(String msg){
        System.out.println(msg);
        throw new RuntimeException("抛出了异常："+ msg);
    }
}

结果如下：

可见使用submit方法时只有在使用Future的get方法时才会抛出异常，并且get方法也会抛出ExecutionException异常。
那么还有一个问题，如果线程中执行方法抛出的异常已经被捕获了，那么submit会怎么处理呢，其实在方法中如果异常已经被捕获了，那么就是方法的正常运行，有异常打印的话在执行的时候就会打印，不会等到调用Future的get方法时候才会打印。测试如下：

public class ExecutorTest1 {

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        ExecutorTest1 test1 = new ExecutorTest1();
        executorService.execute(() -> test1.say("execute方法"));
        Future<?> submitFuture = executorService.submit(() -> test1.say("submit方法"));
        try {
            Object o = submitFuture.get();
            System.out.println("这是submit的返回值："+o);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        executorService.shutdown();
    }

    private void say(String msg){
        System.out.println(msg);
        try{
            throw new RuntimeException("抛出了异常："+ msg);
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

结果如下：

可见execute和submit都正常执行了方法，Future的get方法也获取到了结果，因为say方法没有返回值，所以打印的结果是null。