Spring定时器

    在之前的一篇文章（点击打开链接）介绍过借助quartz.jar实现定时器。但是这种方式太重了，配置繁琐，还需要引入新的包。其实Spring自己有对定时器的支持，借助注解的威力，开发十分简单！效率很高。

    首先看java代码如何使用自带timer。

package com.**.chat.core.common;

import javax.annotation.Resource;

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

import com.**.chat.cache.core.impl.CommonCacheServiceImpl;
import com.**.chat.cache.domain.CoreKey;
import com.**.chat.cache.key.KeyHelper;

/**
 * 从缓存同步配置
 * 
 * @author Administrator
 *
 */
@Component("configSyncTimer")
public class ConfigSyncTimer {

	// 默认开启
	public static boolean			jimiSwitch	= true;
	@Resource
	private CommonCacheServiceImpl	dataCommonCacheService;

	@Scheduled(fixedRate = 30 * 1000)
	private void jimi() {
		CoreKey key = KeyHelper.Data.Chat.getJimiShuntSwitch();
		boolean open = !dataCommonCacheService.exists(key);
		jimiSwitch = open;
	}
}

    此外还需要配置下xml，配完了，就可以跑了。

<?xml version="1.0" encoding="GBK"?>
<beans xmlns="http://www.springframework.org/schema/beans"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:task="http://www.springframework.org/schema/task"  
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd  
        http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.0.xsd">  
    <!-- Enables the Spring Task @Scheduled programming model -->  
    <task:executor id="executor" pool-size="5" />  
    <task:scheduler id="scheduler" pool-size="10" />  
    <task:annotation-driven executor="executor" scheduler="scheduler" />
</beans>

    借助@Scheduled注解，轻松实现timer。这个注解还有另外两种使用方式，我们看下它的定义。

public @interface Scheduled {

	/**
	 * A cron-like expression, extending the usual UN*X definition to include
	 * triggers on the second as well as minute, hour, day of month, month
	 * and day of week.  e.g. <code>"0 * * * * MON-FRI"</code> means once 
	 * per minute on weekdays (at the top of the minute - the 0th second).
	 * @return an expression that can be parsed to a cron schedule
	 */
	String cron() default "";

	/**
	 * Execute the annotated method with a fixed period between the end
	 * of the last invocation and the start of the next.
	 * @return the delay in milliseconds
	 */
	long fixedDelay() default -1;

	/**
	 * Execute the annotated method with a fixed period between invocations.
	 * @return the period in milliseconds
	 */
	long fixedRate() default -1;

}

    cron支持cron表达式类型的timer，支持从配置文件读取cron配置。但是fixedRate和fixedDelay支持硬编码配置。建议大家使用3.2.2版本以上的Spring，这个版本fixedRateString和fixedDelayString支持从配置文件读取配置。

/**
 * Execute the annotated method with a fixed period between the end
 * of the last invocation and the start of the next.
 * @return the delay in milliseconds as a String value, e.g. a placeholder
 * @since 3.2.2
 */
String fixedDelayString() default "";

/**
 * Execute the annotated method with a fixed period between invocations.
 * @return the period in milliseconds as a String value, e.g. a placeholder
 * @since 3.2.2
 */
String fixedRateString() default "";

    个人十分喜欢Spring自带的timer。尤其是将它应用在从缓存中轮询配置或开关的操作。如果每个操作都去读取redis缓存中的配置，大量的网络调用redis很可能把redis打爆。但是如果每个应用实例仅仅是30秒或十分钟拉取一次缓存配置，那对访问redis的压力的改善将会从很高的数量级直接降低到常量级别。