Quartz源码解析 & Cron表达式 &如何获取下一次执行时间

https://blog.csdn.net/MrBack/article/details/104585751

https://www.jianshu.com/p/3f77224ad9d4

 

核心Class：其实很多jar包中都有，比如log4j之类的，因为输出日志的时候其实也用到了

CronExpression.getNextValidTimeAfter(Date date)

大家可以去看源码，使用的时候，new 一个就可以直接调用其中的方法，包括解析expression和获取下一次执行时间

ConfigurationScheduler：结合cron表达式 利用 ScheduledExecutorService 计算出当前时间与下一次执行时间的差值，在指定delay后运行程序。

同时在执行完一次后的finally方法中，计算出下一次的执行时间并重新ScheduledExecutorService.schedule方法，并把返回值Future执行放入ScheduledFuture。

CronScheduledFuture：永远记录着某次 cron任务的执行时间，及使用schedule执行这次任务的返回值 ScheduleFuture

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 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
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package org.apache.logging.log4j.core.config;

import java.util.Date;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 *
 */
public class CronScheduledFuture implements ScheduledFuture {

    private volatile FutureData futureData;

    public CronScheduledFuture(final ScheduledFuture future, final Date runDate) {
        this.futureData = new FutureData(future, runDate);
    }

    public Date getFireTime() {
        return futureData.runDate;
    }

    void reset(final ScheduledFuture future, final Date runDate) {
        futureData = new FutureData(future, runDate);
    }

    @Override
    public long getDelay(final TimeUnit unit) {
        return futureData.scheduledFuture.getDelay(unit);
    }

    @Override
    public int compareTo(final Delayed delayed) {
        return futureData.scheduledFuture.compareTo(delayed);
    }

    @Override
    public boolean cancel(final boolean mayInterruptIfRunning) {
        return futureData.scheduledFuture.cancel(mayInterruptIfRunning);
    }

    @Override
    public boolean isCancelled() {
        return futureData.scheduledFuture.isCancelled();
    }

    @Override
    public boolean isDone() {
        return futureData.scheduledFuture.isDone();
    }

    @Override
    @SuppressWarnings("unchecked")
    public V get() throws InterruptedException, ExecutionException {
        return (V) futureData.scheduledFuture.get();
    }

    @Override
    @SuppressWarnings("unchecked")
    public V get(final long timeout, final TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException {
        return (V) futureData.scheduledFuture.get(timeout, unit);
    }

    private class FutureData {

        private final ScheduledFuture scheduledFuture;
        private final Date runDate;

        FutureData(final ScheduledFuture future, final Date runDate) {
            this.scheduledFuture = future;
            this.runDate = runDate;
        }
    }
}