spring batch: processor called twice after skip - spring-batch

Question

I have a defined a chunk with commit-interval as 10, skip-limit as 10. A processor class manipulates a field by applying some arithmetic operations. In processor class exception occurs for one of the records (say 6th record). After this, once again records from 1 to 5 are processed, 6th is skipped, 7-10 are processed and written to a XML (a custom XML writer class). Since the processor processes 1-5 records twice, the expected field value is wrong as it is calculated twice. Can you please suggest a solution to have the processor process the records only once, skip only the failed record and write the processed records to XML?
Implemented a SkipListener with onSkipInProcess(), onSkipInRead(), onSkipInWrite(). But the output is still the same.
jobconfig.xml
<batch:job id="job">
<batch:step id="step">
<batch:tasklet>
<batch:chunk reader="itemReader" writer="itemWriter"
processor="itemProcessor" commit-interval="10" skip-limit="5" retry-limit="0" >
<batch:skippable-exception-classes>
<batch:include class="java.lang.Exception"/>
</batch:skippable-exception-classes>
<batch:listeners>
<batch:listener ref="skipListener" />
</batch:listeners>
</batch:chunk>
</batch:tasklet>
</batch:step>
</batch:job>
<bean id="itemWriter" class="a.b.XWriter" scope="step"/>
<bean id="skipListener" class="a.b.SkipListener"/>
<bean id="itemProcessor" class="a.b.XProcessor" scope="step"/>
<bean id="itemReader" class="a.b.XReader"/>
ItemReader class:
public class XReader implements ItemReader {
#Autowired
private XRepository classDao;
private List lst = new ArrayList();
private int index= 0;
public Object read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException {
if (lst.isEmpty()) {
lst = classDao.findAll();
}
if (index < lst.size()) {
return lst.get(index++);
} else return null;
}
}
ItemProcessor class:
public class XProcessor<T> implements ItemProcessor<T, T> {
public Object process(Object item) throws Exception {
// logic here
}
ItemWriter class:
public class XWriter <T> implements ItemWriter<T> {
public void write(List<? extends T> items) throws Exception {
// logic here to write to XML
}}
SkipListener class:
public class SkipListener<T,S> implements org.springframework.batch.core.SkipListener<T, S> {
public void onSkipInProcess(T arg0, Throwable arg1) {
}
public void onSkipInRead(Throwable arg0) {
}
public void onSkipInWrite(S arg0, Throwable arg1) {
}
}

Answer 1

When using ItemProcessors in a fault tolerant step, they are expected to be idempotent because there is a risk that they will be called multiple times (as seen in your example). You can read more about this in section 6.3.3 of the documentation here: http://docs.spring.io/spring-batch/reference/html/readersAndWriters.html

Answer 2

You need to have a listener implementation like the below one. Whenever some exception occurs it calls the corresponding method, if you want , you can handle otherwise just leave the method empty. so it will not fail the job.
Also it will not call the processor twice.
xml configuration:
<batch:listeners>
<batch:listener ref="recordSkipListener"/>
</batch:listeners>
Listener class:
public class RecordSkipListener implements SkipListener<Model> {
#Override
public void onSkipInRead(Throwable t) {
}
#Override
public void onSkipInWrite(Model item, Throwable t) {
}
#Override
public void onSkipInProcess(Model item, Throwable t) {
}
}