前言

Java中异步处理任务时，我们通常都会定义线程池来执行任务。然而执行的方式通常主要有两种：

1.直接调用execute方法。

2.调用submit方法，再用Future去get获取执行结果。

这两种方法分别有怎样的区别呢？

分析

我们翻阅Jdk源码则可发现在Executer类中已有定义execute方法如下：

public interface Executor {
 
    /**
     * Executes the given command at some time in the future.  The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the {@code Executor} implementation.
     *
     * @param command the runnable task
     * @throws RejectedExecutionException if this task cannot be
     * accepted for execution
     * @throws NullPointerException if command is null
     */
    void execute(Runnable command);
}

即execute方法可以支持实现了Runnable接口的任务。而我们常用的ExecutorService与Executer的为继承关系。

 从上图信息可以看出ExecutorService中定义submit方法的时候通过重载的方式实现了三个方法，分别可以看出来支持实现了Callable接口的任务、支持实现了Runnable接口的任务。再看关于submit方法定义的描述信息：

 
    /**
     * Submits a value-returning task for execution and returns a
     * Future representing the pending results of the task. The
     * Future's {@code get} method will return the task's result upon
     * successful completion.
     *
     * <p>
     * If you would like to immediately block waiting
     * for a task, you can use constructions of the form
     * {@code result = exec.submit(aCallable).get();}
     *
     * <p>Note: The {@link Executors} class includes a set of methods
     * that can convert some other common closure-like objects,
     * for example, {@link java.security.PrivilegedAction} to
     * {@link Callable} form so they can be submitted.
     *
     * @param task the task to submit
     * @param <T> the type of the task's result
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    <T> Future<T> submit(Callable<T> task);
 
    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's {@code get} method will
     * return the given result upon successful completion.
     *
     * @param task the task to submit
     * @param result the result to return
     * @param <T> the type of the result
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    <T> Future<T> submit(Runnable task, T result);
 
    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's {@code get} method will
     * return {@code null} upon <em>successful</em> completion.
     *
     * @param task the task to submit
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    Future<?> submit(Runnable task);

结论

但从上面两端源码关于方法的注释上即可得出如下的结论。

1.从支持方面来分析，execute()只能执行实现Runnable接口类型的任务;而submit()不仅可以执实现Runnable类型接口的任务，也可以执行实现Callable接口类型的任务。

2.从返回结果来分析，execute()没有返回值，而submit()有在添加Callable类型任务的时候有返回值，我们一般通过返回值查看线程执行情况。这样以来，execute更多的是应用于不关注结果的异步执行场景，而submit则倾向于异步计算任务的场景。

3.从异常处理来分析，submit可以通过Future.get()方法抛出异常，方便我们自定义异常处理；而execute()会终止异常，没有返回值。