第一个Quartz程序

目的

搭建一个Quartz项目，完成如下需求：

每两秒钟打印一次Hello World

搭建Quartz项目

这里搭建的是一个Maven构建的项目，所以需要有一定的Mavan知识。

1. 搭建一个Maven项目

2. 在依赖中加入Quartz的依赖

   <dependency>
       <groupId>org.quartz-scheduler</groupId>
       <artifactId>quartz</artifactId>
       <version>2.3.0</version>
   </dependency>
   <dependency>
       <groupId>org.quartz-scheduler</groupId>
       <artifactId>quartz-jobs</artifactId>
       <version>2.3.0</version>
   </dependency>

3. 创建一个Job，表示要执行的具体内容，这里就是打印字符串Hello World

   package com.wangguitang.freedom.study.quartz.quartz.job;
   
   import org.quartz.Job;
   import org.quartz.JobExecutionContext;
   import org.quartz.JobExecutionException;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   public class HelloJob implements Job {
       private static Logger logger = LoggerFactory.getLogger(HelloJob.class);
   
       @Override
       public void execute(JobExecutionContext jobExecutionContext) throws JobExecutionException {
           logger.info("Hello World");
       }
   }

4. 创建类HelloScheduler

   package com.wangguitang.freedom.study.quartz.quartz;
   
   import com.wangguitang.freedom.study.quartz.quartz.job.HelloJob;
   import org.quartz.*;
   import org.quartz.impl.StdSchedulerFactory;
   
   public class HelloScheduler {
   
       public static void main(String[] args) throws SchedulerException {
           // 创建一个JobDetail实例，将该实例与HelloJob进行绑定
           JobDetail jobDetail = JobBuilder.newJob(HelloJob.class).withIdentity("myjob", "group").build();
   
           // 创建一个Trigger实例，定义该Job立即执行，并且每隔两秒再执行一次
           Trigger trigger = TriggerBuilder
                   .newTrigger()
                   .withIdentity("myTrigger", "group")
                   .startNow()
                   .withSchedule(
                           SimpleScheduleBuilder
                                   .simpleSchedule()
                                   .repeatForever()
                                   .withIntervalInSeconds(2)
                   ).build();
   
           // 创建Scheduler实例
           Scheduler scheduler = StdSchedulerFactory.getDefaultScheduler();
           scheduler.scheduleJob(jobDetail, trigger);
           scheduler.start();
       }
   }

5. 执行HelloScheduler 类的main方法，得到如下结果

   17:19:36 [INFO ] StdSchedulerFactory:1208 - Using default implementation for ThreadExecutor
   17:19:36 [INFO ] SchedulerSignalerImpl:61 - Initialized Scheduler Signaller of type: class org.quartz.core.SchedulerSignalerImpl
   17:19:36 [INFO ] QuartzScheduler:229 - Quartz Scheduler v.2.3.0 created.
   17:19:36 [INFO ] RAMJobStore:155 - RAMJobStore initialized.
   17:19:36 [INFO ] QuartzScheduler:294 - Scheduler meta-data: Quartz Scheduler (v2.3.0) 'MyScheduler' with instanceId 'NON_CLUSTERED'
     Scheduler class: 'org.quartz.core.QuartzScheduler' - running locally.
     NOT STARTED.
     Currently in standby mode.
     Number of jobs executed: 0
     Using thread pool 'org.quartz.simpl.SimpleThreadPool' - with 3 threads.
     Using job-store 'org.quartz.simpl.RAMJobStore' - which does not support persistence. and is not clustered.
   
   17:19:36 [INFO ] StdSchedulerFactory:1362 - Quartz scheduler 'MyScheduler' initialized from default resource file in Quartz package: 'quartz.properties'
   17:19:36 [INFO ] StdSchedulerFactory:1366 - Quartz scheduler version: 2.3.0
   17:19:36 [INFO ] QuartzScheduler:547 - Scheduler MyScheduler_$_NON_CLUSTERED started.
   17:19:36 [INFO ] HelloJob:14 - Hello World
   17:19:38 [INFO ] HelloJob:14 - Hello World
   17:19:40 [INFO ] HelloJob:14 - Hello World
   17:19:42 [INFO ] HelloJob:14 - Hello World
   17:19:44 [INFO ] HelloJob:14 - Hello World
   17:19:46 [INFO ] HelloJob:14 - Hello World
   ...

总结

使用Quartz关键在于Job、JobDetail、Trigger、Scheduler。
Job抽象了要完成的任务，所以需要实现接口Job，在execute方法种编写具体的工作内容。比如上面实例的输出Helllo World。
除了要完成的工作，还需要定义什么时候执行程度。上面示例的要求是：每两秒，我们这里进行设计就是：程序启动时就执行一次任务，然后每过两秒钟再次执行任务。程序如下所示：

            Trigger trigger = TriggerBuilder
                    .newTrigger()
                    .withIdentity("myTrigger", "group")
                    .startNow()
                    .withSchedule(
                            SimpleScheduleBuilder
                                    .simpleSchedule()
                                    .repeatForever()
                                    .withIntervalInSeconds(2)
                    ).build();

定义了要完成的工作和触发的条件，那么这两个东西如何能够进行调度呢，比如说，每过两秒，trigger触发一次，如何知道去执行哪一个工作呢。这时候就需要Scheduler,由它来进行调度。