Java ArrayBlockingQueue 入门指南

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ArrayBlockingQueue：

一个阻塞队列，注意只要有Blocking，都是阻塞的，要阻塞，那容量必须是固定的，在构造方法中指定数量.
如果已经Full，那么put操作会一直等待有空位置出来。
如果已经Empty，那么take会一直等有新元素进来.

示例代码

package com.abc.test;

import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;


/**
 * 注意：以下测试用例只能单独执行.
 */
public class ArrayBlockingQueueTest {

    public static class MyElement {
        final int order;
        final String name;

        public MyElement(String name, int order) {
            this.name = name;
            this.order = order;
        }
    }

    ArrayBlockingQueue<MyElement> arrayBlockingQueue = new ArrayBlockingQueue<>(5);

    //注意线程池数目不能设置为1个.
    ExecutorService pools = Executors.newFixedThreadPool(10);

    /**
     * 先准备5个元素，供每个测试用例使用.
     */
    @Before
    public void init() {
        arrayBlockingQueue.add(new MyElement("1", 1));
        arrayBlockingQueue.add(new MyElement("3", 3));
        arrayBlockingQueue.add(new MyElement("5", 5));
        arrayBlockingQueue.add(new MyElement("10", 10));
        arrayBlockingQueue.add(new MyElement("15", 15));
    }

    /**
     * 只能放5个元素,继续add会报错.
     */
    @Test(expected = IllegalStateException.class)
    public void testFullAndAdd() {
        arrayBlockingQueue.add(new MyElement("16", 16));
    }

    /**
     * 只能放5个元素,offer不成功会返回false.
     */
    @Test
    public void testFullAndOffer() {
        Assert.assertFalse(arrayBlockingQueue.offer(new MyElement("16", 16)));
    }

    /**
     * poll.
     */
    @Test
    public void testPoll() throws InterruptedException {
        MyElement element = arrayBlockingQueue.poll();
        Assert.assertEquals(element.order, 15);
        Assert.assertEquals(arrayBlockingQueue.size(), 4);
        MyElement element2 = arrayBlockingQueue.poll();
        Assert.assertEquals(element2.order, 1);
        Assert.assertEquals(arrayBlockingQueue.size(), 3);
    }

    /**
     * put的时候如果已经full会等待有多余位置出来.
     */
    @Test
    public void testFullAndPut() throws InterruptedException {
        pools.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    arrayBlockingQueue.put(new MyElement("16", 16));
                    System.out.println("after put");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        pools.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(1000 * 5);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                arrayBlockingQueue.poll();
                System.out.println("after poll");
            }
        });

        Thread.sleep(2000);
        {
            MyElement[] array = new MyElement[5];
            arrayBlockingQueue.toArray(array);
            MyElement last = array[array.length - 1];
            Assert.assertEquals(last.order, 15);
        }
        pools.awaitTermination(8, TimeUnit.SECONDS);
        {
            MyElement[] array = new MyElement[5];
            arrayBlockingQueue.toArray(array);
            MyElement last = array[array.length - 1];
            Assert.assertEquals(last.order, 16);
        }

        MyElement element = arrayBlockingQueue.poll();
        Assert.assertEquals(element.order, 3);
        Assert.assertEquals(arrayBlockingQueue.size(), 4);
    }

    /**
     * take如果为空会等待.
     */
    @Test
    public void testTake() throws InterruptedException {
        arrayBlockingQueue.clear();
        pools.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    MyElement element = arrayBlockingQueue.take();
                    Assert.assertEquals(element.order, 100);
                    System.out.println("after put");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        pools.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                try {
                    arrayBlockingQueue.put(new MyElement("100", 100));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            }
        });
        pools.awaitTermination(8, TimeUnit.SECONDS);
    }

}

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