本文介绍 ScheduledExecutorService 在Java1.5以后才出现的定时任务的,在Java5之后,并发线程这块发生了根本的变化,最重要的莫过于新的启动、调度、管理线程的一大堆API了。定时任务在1.5之前是使用 Timer 来实现的,但由于 Timer 有一些问题:
Timer对调度的支持是基于绝对时间,而不是相对时间的,
由此任务对系统时钟的改变是敏感的;ScheduledThreadExecutor只支持相对时间。
Timer的另一个问题在于,如果TimerTask抛出未检查的异常,Timer将会产生无法预料的行为。
Timer线程并不捕获异常,所以TimerTask抛出的未检查的异常会终止timer线程。
这种情况下,Timer也不会再重新恢复线程的执行了;它错误的认为整个Timer都被取消了。
此时,已经被安排但尚未执行的TimerTask永远不会再执行了,新的任务也不能被调度了。
所以建议使用1.5以后的 ScheduledExecutorService 这个定时服务对象
废话不说直接看代码吧:里面有相应的注释
package task;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
/**
官方文档:http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledExecutorService.html
中文版:http://www.apihome.cn/api/java/ScheduledExecutorService.html
*/
public class TaskTest {
/**
* 线程池的管理工具
* 调度型线程池
*/
private final static ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
/**
* 官方案例
*/
public static void beepForAnHour() {
final Runnable beeper = new Runnable() {
public void run() {
System.out.println("beep");
}
};
final ScheduledFuture beeperHandle = scheduler.scheduleAtFixedRate(beeper, 10, 100, TimeUnit.MILLISECONDS);
scheduler.schedule(new Runnable() {
public void run() {
System.out.println("cancel");
/**
* Attempts to cancel execution of this task. This attempt will fail if the task has already completed,
* has already been cancelled, or could not be cancelled for some other reason.
* If successful, and this task has not started when cancel is called, this task should never run. If the task has already started,
* then the mayInterruptIfRunning parameter determines whether the thread executing this task should be interrupted in an attempt to stop the task.
* After this method returns, subsequent calls to isDone() will always return true. Subsequent calls to isCancelled() will always return true if this method returned true.
* 试图取消执行这一任务。这种尝试会失败如果任务已经完成,已经被取消了,或者由于其他原因不能被取消。
* 如果成功的话,这个任务并没有开始时取消,这个任务不应该运行。如果任务已经开始,那么mayInterruptIfRunning参数决定是否应该中断线程执行这个任务,试图阻止这项任务。
* 该方法返回后,后续调用结束()将始终返回true。后续调用isCancelled()将始终返回true,如果这个方法返回true。
*/
beeperHandle.cancel(true);
/**
* 如果这个任务被取消之前完成正常。
* Returns true if this task was cancelled before it completed normally.
*/
System.out.println(beeperHandle.isCancelled());
}
}, 60*60, TimeUnit.MILLISECONDS);
}
/**
* Creates and executes a periodic action that becomes enabled first after the given initial delay,
* and subsequently with the given period; that is executions will commence after initialDelay then initialDelay+period,
* then initialDelay + 2 * period, and so on. If any execution of the task encounters an exception,
* subsequent executions are suppressed. Otherwise, the task will only terminate via cancellation or termination of the executor.
* If any execution of this task takes longer than its period, then subsequent executions may start late, but will not concurrently execute.
* 创建并执行一个周期性的动作成为了第一个在给定的初始延迟之后,随后用给定的时期,这是执行后将开始initialDelay然后initialDelay +,然后initialDelay + 2 *时期,等等。
* 如果任何执行任务遇到异常,后续执行的镇压。否则,只会终止的任务通过取消或终止执行器。如果执行这个任务花费的时间比其期,然后后续执行可能会迟到,但不会同时执行。
* command:执行线程
* initialDelay:初始化延时 启动以后多久执行
* period:两次开始执行最小间隔时间 距离上次执行的时间
* unit:计时单位
*/
public static void scheduleAtFixedRate(){
scheduler.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
System.out.println("scheduleAtFixedRate"+System.currentTimeMillis());
}
}, 1000, 100, TimeUnit.MILLISECONDS);
}
public static void main(String[] args) {
try {
// beepForAnHour();
// scheduleAtFixedRate();
scheduleWithFixedDelay();
// lanuchTimer();
// Thread.sleep(3000);
// taskT();
// Thread.sleep(1000 * 60);
// studow();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* Creates and executes a periodic action that becomes enabled first after the given initial delay,
* and subsequently with the given delay between the termination of one execution and the commencement of the next.
* If any execution of the task encounters an exception, subsequent executions are suppressed. Otherwise,
* the task will only terminate via cancellation or termination of the executor.
* 创建并执行一个周期性的动作成为了第一个在给定的初始延迟之后,随后用给定的延迟之间的终止执行和接下来的毕业典礼。如果任何执行任务遇到异常,后续执行的镇压。
* 否则,只会终止的任务通过取消或终止执行器。
*/
public static void scheduleWithFixedDelay() {
scheduler.scheduleWithFixedDelay(new Runnable() {
public void run() {
System.out.println("scheduleWithFixedDelay---->"+System.currentTimeMillis());
}
}, 1000, 100, TimeUnit.MILLISECONDS);
}
/**
* 关闭执行服务对象
*/
public static void studow() {
scheduler.shutdown();
}
/**
* 凌晨3点钟执行
*/
public static void taskTimr() {
long oneDay = 24 * 60 * 60 * 1000;
long initDelay = getTimeMillis("20:00:00") - System.currentTimeMillis();
initDelay = initDelay > 0 ? initDelay : oneDay + initDelay;
scheduler.scheduleAtFixedRate(
new EchoServer(),
initDelay,
oneDay,
TimeUnit.MILLISECONDS);
}
/**
* 获取指定时间对应的毫秒数
* @param time "HH:mm:ss"
* @return
*/
private static long getTimeMillis(String time) {
try {
DateFormat dateFormat = new SimpleDateFormat("yy-MM-dd HH:mm:ss");
DateFormat dayFormat = new SimpleDateFormat("yy-MM-dd");
Date curDate = dateFormat.parse(dayFormat.format(new Date()) + " " + time);
return curDate.getTime();
} catch (Exception e) {
e.printStackTrace();
}
return 0;
}
}
class EchoServer implements Runnable {
@Override
public void run() {
try {
Thread.sleep(50);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("This is a echo server. The current time is " +
System.currentTimeMillis() + ".");
}
}