发一个自己写的wait()，notify小案例

因为邮箱发送好慢，一般要好几秒才能发一封QQ邮箱，我就写了一个邮件的队列，用一个线程去发邮件，下面是一个模拟的案例。

该案例模拟一个邮件发送过程。EmailQueueSendUtils包含一个邮件队列，由该EmailQueueSendUtils启动后，将会自动检测是否邮箱队列里面有邮件，如果有，就会发送，否则就会等待新邮件来notify阻塞线程。

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;

public class Test2{

    public static void main(String[] args) throws InterruptedException {
        EmailQueueSendUtils emailQueueSendUtils = new EmailQueueSendUtils(new ArrayList<>());

        new Thread(emailQueueSendUtils, "1").start();
        new Thread(emailQueueSendUtils, "2").start();

        for (int i = 0; i < 50; i++) {
            emailQueueSendUtils.addEmailTask(i);
        }
        TimeUnit.SECONDS.sleep(10);
        System.exit(0);
    }
}

class EmailQueueSendUtils implements Runnable{
    private final List<Integer> emailEntityList;

    public EmailQueueSendUtils(List<Integer> emailEntityList){
        this.emailEntityList = emailEntityList;
    }

    @Override
    public void run() {

        while (true){
            System.out.println("进入线程"+Thread.currentThread().getName());
            synchronized (emailEntityList){
                //是否有邮件
                if(emailEntityList.size()>0){
                    while(emailEntityList.size()>0) {
                        Integer emailEntity = emailEntityList.remove(0);
                        System.out.println(Thread.currentThread().getName() + ", " + emailEntity + ", size: " + emailEntityList.size());
                    }
                    //输出完，等待
                    try {
                        emailEntityList.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }else {
                    try {
                        emailEntityList.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }

    }

    public void addEmailTask(Integer emailEntity){
        synchronized (emailEntityList) {
            System.out.println("NUM: "+emailEntity+", 线程："+Thread.currentThread().getName());
            emailEntityList.add(emailEntity);
            emailEntityList.notify();
        }
    }
}