线程池四种拒绝策略

• AbortPolicy 直接抛异常

    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            throw new RejectedExecutionException("Task " + r.toString() +
                                                 " rejected from " +
                                                 e.toString());
        }

• DiscardPolicy 丢弃不处理

 public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
  }

• DiscardOldestPolicy 放弃最老的任务，加入当前任务

public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                e.getQueue().poll();
                e.execute(r);
            }
        }

• CallerRunsPolicy 执行当前任务

 public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                r.run();
            }
        }

线程池实例

package xiezhewan;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * Created by yuxi on 2018/1/24.
 */
public class ThreadPoolDemo {
    public static void main(String[] args) {
        // 线程池核心线程数为1  延时为0 队列为有界队列长度为1， 拒绝策略为直接抛异常
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(1, 1,
                0, TimeUnit.MICROSECONDS,
                new ArrayBlockingQueue(1), new ThreadPoolExecutor.AbortPolicy());
        try {
            for (int i = 0; i < 10; i++) {
                threadPoolExecutor.submit(() -> {
                    try {
                        System.out.println("hello");
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                });

            }
        } catch (Exception e) {
            e.printStackTrace();
            threadPoolExecutor.shutdown();
        }
    }
}

可以看到结果为：

hello
java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@31221be2 rejected from java.util.concurrent.ThreadPoolExecutor@377dca04[Running, pool size = 1, active threads = 1, queued tasks = 1, completed tasks = 0]
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2047)
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:823)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1369)
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112)
    at xiezhewan.ThreadPoolDemo.main(ThreadPoolDemo.java:18)
    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:147)
hello