Quartz源码解析 & Cron表达式 &如何获取下一次执行时间

本是古典何须时尚 2021-08-27 17:01 456阅读 0赞

[https://blog.csdn.net/MrBack/article/details/104585751][https_blog.csdn.net_MrBack_article_details_104585751]

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

/*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements. See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache license, Version 2.0
     * (the "License"); you may not use this file except in compliance with
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     * distributed under the License is distributed on an "AS IS" BASIS,
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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<V> implements ScheduledFuture<V> {
    
        private volatile FutureData futureData;
    
        public CronScheduledFuture(final ScheduledFuture<V> 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;
            }
        }
    }

[https_blog.csdn.net_MrBack_article_details_104585751]: https://blog.csdn.net/MrBack/article/details/104585751
[https_www.jianshu.com_p_3f77224ad9d4]: https://www.jianshu.com/p/3f77224ad9d4