FutureTask与Callable运用
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最近项目需要用到FutureTask异步获取执行结果,并与Callable结合起来运用。
首先,看下FutureTask执行过程:FutureTask可用于异步获取执行结果或取消执行任务的场景。通过传入Runnable或Callable的任务给FutureTask,
直接调用其run方法或者放入线程池执行,然后通过FutureTask的get方法异步获取执行结果。
下面直接看代码。
Service.java ---服务类
//1、new一个线程池,属于成员变量,在项目启动时就初始化 private static final ExecutorService exec = Executors.newFixedThreadPool(100); public FutureTask<List> getFutureTask() { //2、创建FutureTask任务对象,传参Callable FutureTask<List> ft = new FutureTask<List>(new Callable<List>() { //实现Callable的call()方法 @Override public List call() throws Exception { //3、进行业务操作 List re = ""; //4、返回业务结果 return re; } }); //5、把FutureTask任务提交到线程池 exec.submit(ft); //6、并返回FutureTask return ft; }
Action.java----业务类
//6、获取任务,传参objList(业务参数) FutureTask<List> futureTask = taskService.getFutureTask(); //8、get()获取业务操作结果。 List taskList = futureTask.get(20, TimeUnit.SECONDS);
下面看源码实现
public class FutureTask<V> implements RunnableFuture<V> private volatile int state; private static final int NEW = 0; private static final int COMPLETING = 1; private static final int NORMAL = 2; private static final int EXCEPTIONAL = 3; private static final int CANCELLED = 4; private static final int INTERRUPTING = 5; private static final int INTERRUPTED = 6; private Callable<V> callable; private Object outcome; // non-volatile, protected by state reads/writes public FutureTask(Callable<V> callable) { if (callable == null) throw new NullPointerException(); this.callable = callable; this.state = NEW; // ensure visibility of callable } public FutureTask(Runnable runnable, V result) { this.callable = Executors.callable(runnable, result); this.state = NEW; // ensure visibility of callable } //。。。。。。省略 }
FutureTask类实现了RunnableFuture接口,同时RunnableFuture继承了Runnable接口和Future接口。
state修饰变量是volatie,对整个线程是可见的。
outcome ,属于non-valatie,是为了在读写时候做了自我保护
FutureTask提供了2个构造器:FutureTask(Callable<V> callable)和FutureTask(Runnable runnable, V result) 分别实现了Callable和Runnable方法。
调用这个两个构造器时,state状态为NEW
public interface Callable<V> { /** * Computes a result, or throws an exception if unable to do so. * * @return computed result * @throws Exception if unable to compute a result */ V call() throws Exception; }
FutureTask(Callable<V> callable)实现了Callable的call()方法,并返回V结果
public V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException { if (unit == null) throw new NullPointerException(); int s = state; if (s <= COMPLETING && (s = awaitDone(true, unit.toNanos(timeout))) <= COMPLETING) throw new TimeoutException(); return report(s); } /** * Returns result or throws exception for completed task. * * @param s completed state value */ @SuppressWarnings("unchecked") private V report(int s) throws ExecutionException { Object x = outcome; if (s == NORMAL) return (V)x; if (s >= CANCELLED) throw new CancellationException(); throw new ExecutionException((Throwable)x); } protected void set(V v) { if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) { outcome = v; UNSAFE.putOrderedInt(this, stateOffset, NORMAL); // final state finishCompletion(); } }
futureTask.get(20, TimeUnit.SECONDS),通过get()方法获取结果,并设定阻塞时间
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