How to write custom flat file item reader using xml configuration

Question

i am new to spring batch. I am using flat file item reader, configured in xml file. then there is a processor which processes each obj created. I need to pre process contents of file before passing it to file item reader. The processed results/file should not be written to disk. may i know how to do it through xml file configuration. is it though tasklet or extending flat file item reader? then the processor should work as before with no change. i need to introduce a layer before passing the file to flat file item reader.

Answer 1

You can use ItemReadListener for this. ItemReadListener has three callback methods.

beforeRead , afterRead and onReadError.

You can but your logic in beforeRead.

Sample Code for CustomItemReaderListener

public class CustomItemReaderListener implements ItemReadListener<Domain> {



    @Override
        public void beforeRead() {
            System.out.println("ItemReadListener - beforeRead");
//I need to pre process contents of file before passing it to file item reader
// add this logic here 
        }

    @Override
    public void afterRead(Domain item) {
        System.out.println("ItemReadListener - afterRead");
    }

    @Override
    public void onReadError(Exception ex) {
        System.out.println("ItemReadListener - onReadError");
    }

}

Map listeners to Step in XML :

<step id="step1">
    <tasklet>
    <chunk reader="myReader" writer="flatFileItemWriter"
        commit-interval="1" />
        <listeners>         
                 <listener ref="customItemReaderListener" />            
        </listeners>
    </tasklet>
</step>