定时任务之Timer定时器

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package com.myself.study;

import java.util.Timer;
import java.util.TimerTask;

public class TimerDemo {

    public static void main(String[] args) {

        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("timer执行业务逻辑...");
            }
        }, 1000, 1000);

        Timer timer1 = new Timer();
        timer1.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                System.out.println("timer1执行业务逻辑...");
            }
        }, 1000, 1000);
    }
}

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// delay延时之后执行task，只执行一次
public void schedule(TimerTask task, long delay);
// 当时间到达time指定的时间时执行task，只执行一次
public void schedule(TimerTask task, Date time);
// delay延时之后执行一次task，然后每隔period时间执行一次task
public void schedule(TimerTask task, long delay, long period);
// 当时间到达firstTime指定的时间时执行一次task，然后每隔period时间执行一次task
public void schedule(TimerTask task, Date firstTime, long period);
// delay延时之后执行一次task，然后每隔period时间执行一次task
public void scheduleAtFixedRate(TimerTask task, long delay, long period);
// 当时间到达firstTime指定的时间时执行一次task，然后每隔period时间执行一次task
public void scheduleAtFixedRate(TimerTask task, Date firstTime, long period);

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class TimerThread extends Thread {
    /**
     * This flag is set to false by the reaper to inform us that there
     * are no more live references to our Timer object.  Once this flag
     * is true and there are no more tasks in our queue, there is no
     * work left for us to do, so we terminate gracefully.  Note that
     * this field is protected by queue's monitor!
     */
    boolean newTasksMayBeScheduled = true;

    /**
     * Our Timer's queue.  We store this reference in preference to
     * a reference to the Timer so the reference graph remains acyclic.
     * Otherwise, the Timer would never be garbage-collected and this
     * thread would never go away.
     */
    private TaskQueue queue;

    TimerThread(TaskQueue queue) {
        this.queue = queue;
    }

    public void run() {
        try {
            mainLoop();
        } finally {
            // Someone killed this Thread, behave as if Timer cancelled
            synchronized(queue) {
                newTasksMayBeScheduled = false;
                queue.clear();  // Eliminate obsolete references
            }
        }
    }

    /**
     * The main timer loop.  (See class comment.)
     */
    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) {
            }
        }
    }
}