ThreadPoolExecutor构造函数的RejectedExecutionHandler handler参数表示当提交的任务数超过maxmumPoolSize与workQueue之和时，任务会交给RejectedExecutionHandler来处理，此处我们来具体了解一下
（1）ThreadPoolExecutor中默认的饱和策略定义如下：
/** * The default rejected execution handler. */ private static final RejectedExecutionHandler defaultHandler = new AbortPolicy();
（2）ThreadPoolExecutor中获取、设置饱和策略的方法如下：
/** * Sets a new handler for unexecutable tasks. * * @param handler the new handler * @throws NullPointerException if handler is null * @see #getRejectedExecutionHandler */ public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { if (handler == null) throw new NullPointerException(); this.handler = handler; } /** * Returns the current handler for unexecutable tasks. * * @return the current handler * @see #setRejectedExecutionHandler(RejectedExecutionHandler) */ public RejectedExecutionHandler getRejectedExecutionHandler() { return handler; }
（3）RejectedExecutionHandler接口
RejectedExecutionHandler的定义如下：
public interface RejectedExecutionHandler{ //被线程池丢弃的线程处理机制 public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) ; }
（4）AbortPolicy
此策略继承RejectedExecutionHandler接口，其源码如下：
public static class AbortPolicy implements RejectedExecutionHandler{ public AbortPolicy(){} //直接抛出异常 public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) { throw new RejectedExecutionException("Task"+r.toString()+"rejected from"+executor.toString()); } }
（5）自定义饱和策略
实现RejectedExecutionHandler接口，代码如下：
package com.test; import java.util.concurrent.RejectedExecutionHandler; import java.util.concurrent.ThreadPoolExecutor; public class RejectedExecutionHandlerDemo implements RejectedExecutionHandler{ @Override public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) { // TODO Auto-generated method stub System.out.println("线程信息"+r.toString()+"被遗弃的线程池："+executor.toString()); } }
Note：
针对线程池使用 FutureTask 时，如果饱和策略设置为 DiscardPolicy 和 DiscardOldestPolicy，并且在被拒绝的任务的 Future对象上调用了无参 get方法，那么调用线程会一直被阻塞。
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