我們知道在調(diào)用執(zhí)行器的shutdown()方法后，再向執(zhí)行器提交任務(wù)會(huì)被拒絕。執(zhí)行器框架為我們提供了一個(gè)類RejectedExecutionHandler，來(lái)讓我們自定義一些被拒絕任務(wù)的處理邏輯。

首先實(shí)現(xiàn)自定義的拒絕任務(wù)處理邏輯，繼承RejectedExecutionHandler，并實(shí)現(xiàn)rejectedExecution方法。

import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadPoolExecutor;

/**
 * 創(chuàng)建執(zhí)行器拒絕任務(wù)處理器
 *
 * Created by hadoop on 2016/11/3.
 */
public class RejectedTaskController implements RejectedExecutionHandler {
    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        System.out.printf("RejectedTaskController: The task %s has been rejected.\n", r.toString());
        System.out.printf("RejectedTaskController: Executor is %s\n", executor.toString());
        System.out.printf("RejectedTaskController: Executor terminating: %s\n", executor.isTerminating());
        System.out.printf("RejectedTaskController: Executor terminated: %s\n", executor.isTerminated());
    }
}

模擬一個(gè)任務(wù)線程，實(shí)現(xiàn)Runnable接口。

import java.util.concurrent.TimeUnit;

/**
 *
 * Created by hadoop on 2016/11/3.
 */
public class Task implements Runnable {
    private String name;

    public Task(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        long duration = (long)(Math.random() * 10);

        System.out.printf("Task: %s will run during %d seconds\n", name, duration);

        try {
            TimeUnit.SECONDS.sleep(duration);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public String toString() {
        return this.name;
    }
}

在主線程類中，首先初始化自定義的被拒絕任務(wù)處理器，然后把它賦值給執(zhí)行器。模擬在shutdown()方法后提交任務(wù)，并觀察結(jié)果。

import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;

/**
 * 處理在執(zhí)行器中被拒絕的任務(wù)
 *
 * 我們使用shutdown方法來(lái)關(guān)閉執(zhí)行器，但是如果當(dāng)前有正在執(zhí)行的任務(wù)，執(zhí)行器會(huì)等待任務(wù)執(zhí)行完成才會(huì)關(guān)閉。
 * 但這個(gè)時(shí)候執(zhí)行期已經(jīng)不再接受任何任務(wù)了，我們發(fā)送任務(wù)給執(zhí)行器會(huì)被拒絕。
 * ThreadPoolExecutor提供了一套機(jī)制了處理這些被拒絕的任務(wù)。
 *
 * 我們定義了一個(gè)執(zhí)行器拒絕任務(wù)儲(chǔ)麗麗RejectedTaskController.
 * 在方法rejectedExecution(Runnable r, ThreadPoolExecutor executor)中處理被拒絕的任務(wù)。
 *
 * 需要通過(guò)執(zhí)行器的setRejectedExecutionHandler(controller)方法來(lái)給執(zhí)行器設(shè)置決絕任務(wù)處理器類。
 *
 * 當(dāng)有任務(wù)發(fā)送給處理器的時(shí)候，會(huì)檢查處理器是否被shutdown，如果shutdown那么就會(huì)調(diào)用拒絕任務(wù)處理器。
 * 如果沒(méi)有定義這個(gè)拒絕任務(wù)處理器，那么就會(huì)拋出RejectedExecutionException異常。
 *
 * Created by hadoop on 2016/11/3.
 */
public class Main {
    public static void main(String[] args) {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newCachedThreadPool();

        RejectedTaskController controller = new RejectedTaskController();

        executor.setRejectedExecutionHandler(controller);

        for (int i = 0; i < 3; i++) {
            Task task = new Task("Task" + i);
            executor.submit(task);
        }

        executor.shutdown();

        Task task = new Task("RejectTask");
        executor.submit(task);
    }
}

控制臺(tái)結(jié)果：

RejectedTaskController: The task java.util.concurrent.FutureTask@5d86aad9 has been rejected.
Task: Task1 will run during 2 seconds
Task: Task0 will run during 0 seconds
Task: Task2 will run during 8 seconds
RejectedTaskController: Executor is java.util.concurrent.ThreadPoolExecutor@767ca7f0[Shutting down, pool size = 3, active threads = 3, queued tasks = 0, completed tasks = 0]
RejectedTaskController: Executor terminating: true
RejectedTaskController: Executor terminated: false