Spring基础：快速入门spring boot（5）：Spring中的Cron--Scheduling

本篇文章将在将介绍如何在spring中使用类似于Linux/Unix中的Cron的任务管理模块。

创建一个Cron任务的类

package com.example;

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

import java.text.SimpleDateFormat;
import java.util.Date;

@Component
public class CronTasks {
private SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
@Scheduled(fixedRate = 2000)
public void cronDemoTasks(){
System.out.println("CronTask: Hello, this is for test : " + dateFormat.format(new Date()));
}
}

修改DemoApplication

只需要加入@EnableScheduling注解即可

执行输出

因为使用out打出来的信息, 结果的确认在Console的输出即可看到.

.   ____          _            __ _ _
/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/  ___)| |_)| | | | | || (_| |  ) ) ) )
'  |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot ::        (v1.4.2.RELEASE)

2016-12-09 07:04:59.491  INFO 4092 --- [           main] com.example.DemoApplication              : Starting DemoApplication on vcc-PC with PID 4092 (C:\Users\Administrator\IdeaProjects\demo\target\classes started by Administrator in C:\Users\Administrator\IdeaProjects\demo)
2016-12-09 07:04:59.495  INFO 4092 --- [           main] com.example.DemoApplication              : No active profile set, falling back to default profiles: default
2016-12-09 07:04:59.581  INFO 4092 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@30ee2816: startup date [Fri Dec 09 07:04:59 CST 2016]; root of context hierarchy
2016-12-09 07:05:01.304  INFO 4092 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2016-12-09 07:05:01.319  INFO 4092 --- [           main] o.apache.catalina.core.StandardService   : Starting service Tomcat
2016-12-09 07:05:01.321  INFO 4092 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.6
2016-12-09 07:05:01.492  INFO 4092 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2016-12-09 07:05:01.493  INFO 4092 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1922 ms
2016-12-09 07:05:01.621  INFO 4092 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]
2016-12-09 07:05:01.625  INFO 4092 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2016-12-09 07:05:01.625  INFO 4092 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2016-12-09 07:05:01.625  INFO 4092 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2016-12-09 07:05:01.626  INFO 4092 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2016-12-09 07:05:01.879  INFO 4092 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@30ee2816: startup date [Fri Dec 09 07:04:59 CST 2016]; root of context hierarchy
2016-12-09 07:05:01.952  INFO 4092 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/greeting]}" onto public com.example.User com.example.DemoApplication.greeting(java.lang.String)
2016-12-09 07:05:01.954  INFO 4092 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2016-12-09 07:05:01.954  INFO 4092 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2016-12-09 07:05:01.980  INFO 4092 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-12-09 07:05:01.980  INFO 4092 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-12-09 07:05:02.017  INFO 4092 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-12-09 07:05:02.239  INFO 4092 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2016-12-09 07:05:02.249  INFO 4092 --- [           main] s.a.ScheduledAnnotationBeanPostProcessor : No TaskScheduler/ScheduledExecutorService bean found for scheduled processing
CronTask: Hello, this is for test : 07:05:02
2016-12-09 07:05:02.299  INFO 4092 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2016-12-09 07:05:02.303  INFO 4092 --- [           main] com.example.DemoApplication              : Started DemoApplication in 3.341 seconds (JVM running for 3.831)
CronTask: Hello, this is for test : 07:05:04
CronTask: Hello, this is for test : 07:05:06
CronTask: Hello, this is for test : 07:05:08
CronTask: Hello, this is for test : 07:05:10
CronTask: Hello, this is for test : 07:05:12
CronTask: Hello, this is for test : 07:05:14
CronTask: Hello, this is for test : 07:05:16
CronTask: Hello, this is for test : 07:05:18
CronTask: Hello, this is for test : 07:05:20
CronTask: Hello, this is for test : 07:05:22
......

可以清楚地看到，每格两秒，此Task就会被调用执行一次。

Cron风格方式

与Ctrontab写法的区别，被人熟知的Crontab的写法如下：

项目	说明
格式	*　　*　　*　　*　　*　　command
说明	分　时　日　月　周　命令
第1列	分钟1～59 每分钟用或者 /1表示
第2列	小时1～23（0表示0点）
第3列	日期1～31
第4列	月份1～12
第5列	星期0～6（0表示星期天）
第6列	要运行的命令

而Scheduling则是如下的格式

项目	说明
格式	*　　*　　*　　*　　*　　*
第1列	秒
第2列	分钟
第3列	小时
第4列	日期
第5列	月份
第6列	星期

简单来说，精度精确到秒，命令行无需指定，显然此处是使用spring的类反射机制由声明的注解处的函数所提供对应定期调用的功能。

Cron风格常用写法

写法	说明
“0 0 * * * *”	the top of every hour of every day.
“/10 * * * *”	every ten seconds.
“0 0 8-10 * * *”	8, 9 and 10 o’clock of every day.
“0 * 6,19 * * *”	6:00 AM and 7:00 PM every day.
“0 0/30 8-10 * * *”	8:00, 8:30, 9:00, 9:30 and 10 o’clock every day.
“0 0 9-17 * * MON-FRI”	on the hour nine-to-five weekdays
“0 0 0 25 12 ?”	every Christmas Day at midnight

Cron风格验证

将fixedRate的设定改成cron风格，变成没3秒调用一次。

@Scheduled(fixedRate = 2000)

-〉

@Scheduled(cron=”/3 * * * *”)

结果确认

如下则是部分输出结果，从中可以清晰地确认到3秒钟被调用的结果。

CronTask: Hello, this is for test : 07:23:03
CronTask: Hello, this is for test : 07:23:06
CronTask: Hello, this is for test : 07:23:09
CronTask: Hello, this is for test : 07:23:12