Java阻塞队列示例

今天我们将研究Java的BlockingQueue。java.util.concurrent.BlockingQueue是一种支持在检索和删除元素时等待队列变为非空，并在添加元素时等待队列中有可用空间的Java队列。

Java 阻塞队列

Java的BlockingQueue不接受空值，如果尝试将空值存储在队列中，会抛出NullPointerException异常。Java的BlockingQueue实现是线程安全的。所有的排队方法具有原子性，并且使用内部锁或其他形式的并发控制。Java的BlockingQueue接口是Java集合框架的一部分，主要用于实现生产者和消费者问题。在BlockingQueue中，我们不需要担心生产者等待空间可用或消费者等待对象可用，因为这由BlockingQueue的实现类处理。Java提供了几种BlockingQueue的实现，例如ArrayBlockingQueue、LinkedBlockingQueue、PriorityBlockingQueue、SynchronousQueue等。在实现生产者和消费者问题时，我们将使用ArrayBlockingQueue实现。以下是一些重要的方法，你应该了解。

• put(E e): This method is used to insert elements to the queue. If the queue is full, it waits for the space to be available.
• E take(): This method retrieves and remove the element from the head of the queue. If queue is empty it waits for the element to be available.

我们现在来使用Java的BlockingQueue来实现生产者消费者问题。

Java BlockingQueue示例-消息

只是一个普通的Java对象，它将由生产者生成并添加到队列中。你也可以称它为有效载荷或队列消息。

package com.Olivia.concurrency;

public class Message {
    private String msg;
    
    public Message(String str){
        this.msg=str;
    }

    public String getMsg() {
        return msg;
    }

}

Java 阻塞队列示例-生产者

生成器类将创建消息并将其放入队列中。

package com.Olivia.concurrency;

import java.util.concurrent.BlockingQueue;

public class Producer implements Runnable {

    private BlockingQueue<Message> queue;
    
    public Producer(BlockingQueue<Message> q){
        this.queue=q;
    }
    @Override
    public void run() {
        //produce messages
        for(int i=0; i<100; i++){
            Message msg = new Message(""+i);
            try {
                Thread.sleep(i);
                queue.put(msg);
                System.out.println("Produced "+msg.getMsg());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        //adding exit message
        Message msg = new Message("exit");
        try {
            queue.put(msg);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

Java阻塞队列示例-消费者

当接收到退出信息时，消费者类会处理队列中的消息并终止。

package com.Olivia.concurrency;

import java.util.concurrent.BlockingQueue;

public class Consumer implements Runnable{

private BlockingQueue<Message> queue;
    
    public Consumer(BlockingQueue<Message> q){
        this.queue=q;
    }

    @Override
    public void run() {
        try{
            Message msg;
            //consuming messages until exit message is received
            while((msg = queue.take()).getMsg() !="exit"){
            Thread.sleep(10);
            System.out.println("Consumed "+msg.getMsg());
            }
        }catch(InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Java 阻塞队列示例 – 服务

最后我们需要为生产者和消费者创建一个BlockingQueue服务。这个生产者消费者服务将创建一个固定大小的BlockingQueue，与生产者和消费者共享。这个服务将启动生产者和消费者线程并退出。

package com.Olivia.concurrency;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

public class ProducerConsumerService {

    public static void main(String[] args) {
        //Creating BlockingQueue of size 10
        BlockingQueue<Message> queue = new ArrayBlockingQueue<>(10);
        Producer producer = new Producer(queue);
        Consumer consumer = new Consumer(queue);
        //starting producer to produce messages in queue
        new Thread(producer).start();
        //starting consumer to consume messages from queue
        new Thread(consumer).start();
        System.out.println("Producer and Consumer has been started");
    }

}

以下是上述Java BlockingQueue示例程序的输出。

Producer and Consumer has been started
Produced 0
Produced 1
Produced 2
Produced 3
Produced 4
Consumed 0
Produced 5
Consumed 1
Produced 6
Produced 7
Consumed 2
Produced 8
...

Java中的线程睡眠（Thread sleep）用于生产者和消费者以某种延迟生成和消费消息。