Java 线程池submit和execute

submit方法：

public abstract class AbstractExecutorService implements ExecutorService {

    protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
        return new FutureTask<T>(runnable, value);
    }

    protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
        return new FutureTask<T>(callable);
    }

    public Future<?> submit(Runnable task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<Void> ftask = newTaskFor(task, null);
        execute(ftask);
        return ftask;
    }

    public <T> Future<T> submit(Runnable task, T result) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<T> ftask = newTaskFor(task, result);
        execute(ftask);
        return ftask;
    }

    public <T> Future<T> submit(Callable<T> task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<T> ftask = newTaskFor(task);
        execute(ftask);
        return ftask;
    }
   //....
}

public interface RunnableFuture<V> extends Runnable, Future<V> {
    /**
     * Sets this Future to the result of its computation
     * unless it has been cancelled.
     */
    void run();
}

   protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
            return new FutureTask<T>(runnable, value);
        }

        protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
            return new FutureTask<T>(callable);
        }

public class FutureTask<V> implements RunnableFuture<V> {

    private final java.util.concurrent.FutureTask.Sync sync;

    public FutureTask(Callable<V> callable) {
        if (callable == null)
            throw new NullPointerException();
        sync = new java.util.concurrent.FutureTask.Sync(callable);
    }

    public FutureTask(Runnable runnable, V result) {
        sync = new java.util.concurrent.FutureTask.Sync(Executors.callable(runnable, result));
    }
    //....
}

submit返回的最终是FutureTask对象

execute方法：

public interface Executor {

    void execute(Runnable command);
}

具体的实现在ThreadPoolExecutor类中

    public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();

        int c = ctl.get();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        else if (!addWorker(command, false))
            reject(command);
    }

submit内部调用execute

submit有返回值

submit方便exception处理

submit的demo:

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class Main {
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newCachedThreadPool();
        List<Future<String>> resultList = new ArrayList<Future<String>>();

        // 创建10个任务并执行
        for (int i = 0; i < 10; i++) {
            // 使用ExecutorService执行Callable类型的任务，并将结果保存在future变量中
            Future<String> future = executorService.submit(new TaskWithResult(i));
            // 将任务执行结果存储到List中
            resultList.add(future);
        }
        executorService.shutdown();

        // 遍历任务的结果
        for (Future<String> fs : resultList) {
            try {
                System.out.println(fs.get()); // 打印各个线程（任务）执行的结果
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                executorService.shutdownNow();
                e.printStackTrace();
                return;
            }
        }
    }
}
class TaskWithResult implements Callable<String> {
    private int id;

    public TaskWithResult(int id) {
        this.id = id;
    }

    /**
     * 任务的具体过程，一旦任务传给ExecutorService的submit方法，则该方法自动在一个线程上执行。
     *
     * @return
     * @throws Exception
     */
    public String call() throws Exception {
        System.out.println("call()方法被自动调用,干活！！！             " + Thread.currentThread().getName());
        if (new Random().nextBoolean())
            throw new TaskException("Meet error in task." + Thread.currentThread().getName());
        // 一个模拟耗时的操作
        for (int i =9; i > 0; i--)
            ;
        return "call()方法被自动调用，任务的结果是：" + id + "    " + Thread.currentThread().getName();
    }
}

class TaskException extends Exception {
    public TaskException(String message) {
        super(message);
    }
}

call()方法被自动调用,干活！！！             pool-1-thread-5
call()方法被自动调用,干活！！！             pool-1-thread-1
call()方法被自动调用,干活！！！             pool-1-thread-2
call()方法被自动调用,干活！！！             pool-1-thread-4
call()方法被自动调用,干活！！！             pool-1-thread-6
call()方法被自动调用,干活！！！             pool-1-thread-6
call()方法被自动调用,干活！！！             pool-1-thread-4
call()方法被自动调用,干活！！！             pool-1-thread-2
call()方法被自动调用,干活！！！             pool-1-thread-3
call()方法被自动调用,干活！！！             pool-1-thread-7
call()方法被自动调用，任务的结果是：0    pool-1-thread-1
call()方法被自动调用，任务的结果是：1    pool-1-thread-2
java.util.concurrent.ExecutionException: com.company.TaskException: Meet error in task.pool-1-thread-3
    at java.util.concurrent.FutureTask.report(FutureTask.java:122)
    at java.util.concurrent.FutureTask.get(FutureTask.java:192)
    at com.company.Main.main(Main.java:29)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: com.company.TaskException: Meet error in task.pool-1-thread-3
    at com.company.TaskWithResult.call(Main.java:56)
    at com.company.TaskWithResult.call(Main.java:40)
    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)

Runnable和Callable的区别是，
(1)Callable规定的方法是call(),Runnable规定的方法是run().
(2)Callable的任务执行后可返回值，而Runnable的任务是不能返回值得
(3)call方法可以抛出异常，run方法不可以
(4)运行Callable任务可以拿到一个Future对象，表示异步计算的结果。它提供了检查计算是否完成的方法，以等待计算的完成，并检索计算的结果。通过Future对象可以了解任务执行情况，可取消任务的执行，还可获取执行结果。

http://blog.csdn.net/yuzhiboyi/article/details/7775266

http://blog.csdn.net/zhangzhaokun/article/details/6615454

http://blog.csdn.net/xtwolf008/article/details/7713580