1、介绍

在java中实现定时任务有几种方式：

1、自己写代码，解析cron表达式，或者sleep多长时间在执行一次

2、使用内置的timer类来实现

3、使用ScheduledThreadPoolExecutor（和timer有区别，timer一个任务抛异常，所有任务都不能用了）

3、利用开源的quartz，结合spring进行使用

下面重点讲解Timer

2、代码

public class TimerTest {    public static void main(String[] args) {        Timer timer = new Timer();        timer.schedule(new TimerTask() {  //public abstract class TimerTask implements Runnable            [@Override](https://my.oschina.net/u/1162528)            public void run() {                //Fixme Do SameThing                System.out.println("Task1");            }        }, 1000, 1 * 1000);        timer.schedule(new TimerTask() {            [@Override](https://my.oschina.net/u/1162528)            public void run() {                //fixme 一个timer可以启动多个定时任务，他里面维护了一个queue                //fixme private final TaskQueue queue = new TaskQueue();                //fixme private final TimerThread thread = new TimerThread(queue);                //fixme queue.add(task);                System.out.println("Task2");            }        }, 200, 2 * 1000);    }    /**     * TimerThread 的run方法调用mainLoop     *///    private void mainLoop() {//        while (true) {//            try {//                TimerTask task;//                boolean taskFired;//                synchronized(queue) {//                    // Wait for queue to become non-empty//                    while (queue.isEmpty() && newTasksMayBeScheduled)//                        queue.wait();//                    if (queue.isEmpty())//                        break; // Queue is empty and will forever remain; die////                    // Queue nonempty; look at first evt and do the right thing//                    long currentTime, executionTime;//                    task = queue.getMin();//                    synchronized(task.lock) {//                        if (task.state == TimerTask.CANCELLED) {//                            queue.removeMin();//                            continue;  // No action required, poll queue again//                        }//                        currentTime = System.currentTimeMillis();//                        executionTime = task.nextExecutionTime;//                        if (taskFired = (executionTime<=currentTime)) {//                            if (task.period == 0) { // Non-repeating, remove//                                queue.removeMin();//                                task.state = TimerTask.EXECUTED;//                            } else { // Repeating task, reschedule//                                queue.rescheduleMin(//                                        task.period<0 ? currentTime   - task.period//                                                : executionTime + task.period);//                            }//                        }//                    }//                    if (!taskFired) // Task hasn't yet fired; wait//                        queue.wait(executionTime - currentTime);//                }//                if (taskFired)  // Task fired; run it, holding no locks//                    task.run();//            } catch(InterruptedException e) {//            }//        }//    }}