Spring 带有任务执行器的批处理小任务

Question

I got a weird issue about spring batch tasklet step with task-executor. The configuration is normal and simple, just a tasklet (no chunk-oriented) as below:

<batch:job id="MyJob" restartable="false">
        <batch:step id="MyJob.Step1">
            <batch:tasklet ref="someBean" task-executor="simpleAsyncTaskExecutor" throttle-limit="1"/>
        </batch:step>
</batch:job>

The someBean is an instance implementated Tasklet interface. The stange thing is when I launch the job, the execute method called twice:

@Override
    public RepeatStatus execute(StepContribution contribution, ChunkContext chunkContext) throws Exception {

    // some logic and no exception

    return RepeatStatus.FINISHED;
}

actually two threads are created and executed the logic twice. And if I change task-executor to the normal task-executor="syncTaskExecutor" (org.springframework.core.task.SyncTaskExecutor), only one thread created and execute() invoked once.

Does anyone encountered this case and could give some idea? I really do not know "who" and "when" created two threads? Thanks

Answer 1

When you specify an asynchronous task-executor , your tasklet will be executed concurrently by multiple threads. The limit can be set using throttle-limit which defaults to 4. In your case, two threads will execute the tasklet.

On the other hand, the SyncTaskExecutor will run the tasklet in the calling thread, which means only once since there are no other threads created.