通过Java反射机制动态修改TimerTask的执行周期并立即生效

import java.lang.reflect.Field;
import java.util.Date;
import java.util.TimerTask;

/**
 * SendMailTask
 */
public abstract class SendMailTask extends TimerTask {

    long period = 0;

    public void setPeriod(long period) {
        Date now = new Date();
        // 设置下一次执行时间i
        long nextExecutionTime = now.getTime() + period;
        setDeclaredField(TimerTask.class, this, "nextExecutionTime", nextExecutionTime);
        // 修改执行周期
        setDeclaredField(TimerTask.class, this, "period", period);
    }

    //通过反射修改字段的值
    static boolean setDeclaredField(Class<?> clazz, Object obj, String name, Object value) {
        try {
            Field field = clazz.getDeclaredField(name);
            field.setAccessible(true);
            field.set(obj, value);
            return true;
        } catch (Exception ex) {
            ex.printStackTrace();
            return false;
        }
    }
}

测试：

import SendMailTask;
import java.time.LocalDateTime;
import java.util.Timer;

public class TimerTest2 {
    static int i = 0;
    static int k = 0;
    static int n = 0;
    /**
     * 获取两数之间的随机数
     * @param m
     * @param n
     * @return
     */
    public static int getRandom(int m, int n) {
        int max = Math.max(m,n);
        int min = Math.min(m,n);
        int mid = max - min;
        // 产生随机数
        int num =  (int) (Math.random() * (mid + 1)) + min;
        return num;
    }

    public static void main(String[] args) {
        int total = 10;
        int pause = 5;
        int interval = 1;
        // timer
        Timer timer = new Timer(); // 定时任务
        SendMailTask task = new SendMailTask() {
            int count = 0; // 循环计数器
            // timerTask执行体
            @Override
            public synchronized void run() {
                ++k;
                ++n;
                System.out.println("hello，这是第"+k+"次输出！当前时间："+ LocalDateTime.now());
                i++;
                count++;
                if (count == total) {
                    System.err.println("完成时间: " + LocalDateTime.now());
                    timer.cancel(); // 取消定时器
                }
                // 每发完pause，暂停一段时间
                if (count % pause == 0 && count != total) {
                    try {
                        System.out.println("打印完" + pause + "条了," + interval + "分钟后继续: " + LocalDateTime.now());
                        n = 0;
                        Thread.sleep(interval * 60000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                if(n > 0 && n % 3 == 0) {
                    try {
                        n = 0;
                        System.out.println("2秒后继续。。。。"+ LocalDateTime.now());
                        Thread.sleep(2000);
                        //wait(2000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                // 修改任务周期
                if(i>0 && i % 3 == 0) {
                    setPeriod(5000);
                    System.out.println("间隔修改为5秒。。。"+ LocalDateTime.now());
                }
            }
        };
        timer.schedule(task, 2000, 3000);
    }
}

import SendMailTask;
import java.time.LocalDateTime;
import java.util.Timer;

public class TimerTest2 {
    static int i = 0;
    static int k = 0;
    static int n = 0;
    /**
     * 获取两数之间的随机数
     * @param m
     * @param n
     * @return
     */
    public static int getRandom(int m, int n) {
        int max = Math.max(m,n);
        int min = Math.min(m,n);
        int mid = max - min;
        // 产生随机数
        int num =  (int) (Math.random() * (mid + 1)) + min;
        return num;
    }

    public static void main(String[] args) {
        int total = 10;
        int pause = 5;
        int interval = 1;
        int min = 5;
        int max = 20;
        int amount = 3;
        // timer
        Timer timer = new Timer(); // 定时任务
        SendMailTask task = new SendMailTask() {
            int count = 0; // 循环计数器
            // timerTask执行体
            @Override
            public synchronized void run() {
                ++k;
                ++n;
                System.out.println("hello，这是第"+k+"次输出！当前时间："+ LocalDateTime.now());
                i++;
                count++;
                if (count == total) {
                    System.err.println("完成时间: " + LocalDateTime.now());
                    timer.cancel(); // 取消定时器
                }
                // 每发完pause，暂停一段时间
                if (count % pause == 0 && count != total) {
                    try {
                        System.out.println("打印完" + pause + "条了," + interval + "分钟后继续: " + LocalDateTime.now());
                        n = 0;
                        i = 0;
                        Thread.sleep(interval * 60000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                if(n > 0 && n % amount == 0) {
                    try {
                        n = 0;
                        int seconds1 = getRandom(min,max);
                        System.out.println(seconds1 +"秒后继续。。。。"+ LocalDateTime.now());
                        Thread.sleep(seconds1 * 1000 );
                        //wait(2000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                // 修改任务周期
                if(i>0 && i % amount == 0) {
                    i = 0;
                    int seconds2 = Math.round(getRandom(min,max) / amount);
                    setPeriod(seconds2 * 1000);
                    System.out.println("间隔修改为"+ seconds2 + "秒。。。"+ LocalDateTime.now());
                }
            }
        };
        timer.schedule(task, 2000, Math.round( (getRandom(min,max) / amount) * 1000 )+1);
    }
}

参考文章链接：
https://www.iteye.com/blog/chen-yongkai-1673241
https://blog.csdn.net/yasi_xi/article/details/25626113