Spring Batch ItemProcessListener Example

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ItemProcessorListener Example, Spring Batch

For a recent work project I've been up to my ears in Spring Batch, and besides documentation, when I am thrown into a new project I tend to use good examples of people using the library to supplement my learning. So when we decided that we needed finer grain tracking of each item being processed, I went in search of examples of item procesor listeners.

The number one hit on google for spring batch listeners examples was mykongs excellent example. The problem of course, is that him and everyone else I came accross were never using the ItemProcessListener. The closest thing to an example I could find was this stackoverflow question.

The ItemProcessListener allows you to hook into the 3 core methods of the item workflow. You can hook into it before the item is processed, after, and when the processor throws an error. Throwing an error while you're in one of the three listener methods will result in a failed step, so be care to check your exceptions!

The three methods you can use are intuitively named:

One of the things you need to watch out for is that if your processor can return null (i.e. you are filtering items out), then the afterProcess/onProcessError will also recieve the null object. Just one of those things to be aware of.

To create an item processor you need to implement the ItemProcessListener<T,S> interface:

package com.example;

public class MyExampleProcessorListener implements ItemProcessListener<Baz, Boz>{
    @Override
    public void beforeProcess(Baz baz){
        if(baz == null){
            //...
        }
        //...
    }

    @Override
    public void afterProcess(Baz baz, Boz boz){
        //..
    }

    @Override
    public void onProcessError(Baz baz, Exception e){
        //..
    }
}

And in your configuration you need to have your step configured with your listener specified in the configuration of your step:

<bean id="exampleListener" class="com.example.MyExampleProcessorListener"  scope="step"/>

<batch:job id="example" job-repository="jobRepository">
    <batch:step id="exampleStep">
        <batch:tasklet transaction-manager="transactionManager">
            <batch:chunk reader="" processor="" writer="" commit-interval="" />
        </batch:tasklet>
        <batch:listeners>
            <batch:listener ref="exampleListener" />
        </batch:listeners>
    </batch:step>
</batch:job>

One of the things that tripped me up for a little bit was that the listeners tag in your XML setup must be within the step and not inside the tasklet. Placing the listeners inside your chunk, tasklet, or anywhere else strange will result in the code simply not executing. One of the useful things that I walked away from that silly encounter was that XSD files and xmllint can be very helpful when you're troubleshooting your xml configuration files.

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