Spring Batch简单入门（四） - Job启动与监控

r囧r小猫 2022-05-13 07:44 561阅读 0赞

接[上一章][Link 1]，本章我们介绍Job的启动与监听。

### Running a Job ###

Spring Boot默认支持自动启动已配置好的Job，我们可以通过配置项`**spring.batch.job.enabled=false**`来禁止Spring容器自动启动Job。正常情况下，当我们通过调度器调用Job时，整个流程如下：  
![这里写图片描述][70]

> A [JobExecution][],is the primary storage mechanism for what actually happened during a run and contains many more properties that must be controlled and persisted

当Job启动之后，一个JobExecution对象会传递给Job的执行方法体，JobExecution负责存储Job执行期间执行信息，比如：状态、开始结束时间、最终退出状态、异常信息、执行上下文等等，并且最终会被传递给调用方。

run job from scheduler
    Job [176] start 2018-09-11 15:41:41
    Job [176] finish 2018-09-11 15:41:42
    Job [176] status COMPLETED

然而，当我们试图从HTTP请求中启动Job时，我们就需要注意，Job是以异步的方式被启动，这样JobExecution会立即返回给调用者，实际Job的最后退出状态会是**UNKNOWN**。  
![这里写图片描述][70 1]  
这是因为为批处理进程长时间保持HTTP连接并非最佳应用实践。整个流程如下图所示：  
![这里写图片描述][70 2]

以JobLauncher启动Job

@Service
    @Slf4j
    public class JobLaunchService { 
        @Autowired
        private JobLauncher jobLauncher;
    
        public JobResult launchJob(Job job) {
            try {
                JobParameters jobParameters = new JobParametersBuilder()
                        .addDate("timestamp", Calendar.getInstance().getTime())
                        .toJobParameters();
                JobExecution jobExecution = jobLauncher.run(job, jobParameters);
                return JobResult.builder()
                        .jobName(job.getName())
                        .jobId(jobExecution.getJobId())
                        .jobExitStatus(jobExecution.getExitStatus())
                        .timestamp(Calendar.getInstance().getTimeInMillis())
                        .build();
            } catch (Exception e) {
                log.error(e.getMessage());
                throw new RuntimeException("launch job exception ", e);
            }
        }
    }

### Intercepting Job Execution ###

public interface JobExecutionListener {
    
        void beforeJob(JobExecution jobExecution);
    
        void afterJob(JobExecution jobExecution);
    
    }

*更多源码请参考:*

[https://github.com/ypmc/spring-cloud/tree/master/spring-batch][https_github.com_ypmc_spring-cloud_tree_master_spring-batch]

[Link 1]: https://blog.csdn.net/kangkanglou/article/details/82623599
[70]: /images/20220513/b00eef6c0f6a46fa8d93e80d97f4c542.png
[JobExecution]: https://docs.spring.io/spring-batch/4.0.x/reference/html/domain.html#JobExecution
[70 1]: /images/20220513/70457482491542acbc9f0847ac375071.png
[70 2]: /images/20220513/bbb6e65c9f24434cb447f5d4c40b21d7.png
[https_github.com_ypmc_spring-cloud_tree_master_spring-batch]: https://github.com/ypmc/spring-cloud/tree/master/spring-batch