Insert & Update from single Spring Batch ItemReader - spring-batch

Question

My process transforms the data into SCD2 pattern. Thus, any update in the source data culminates into updating the end_date & active_ind in the dimension table and inserting a new record.
I have configured the SQL in an ItemReader implementation which identifies the records which got changed in the source data.
I need help/suggestion on how to route the data to 2 writers, 1 each for update & insert?

Answer 1

There is a general pattern in Spring for this type of use case and not necessarily for Spring Batch using Classifier Interface.
You can use BackToBackPatternClassifier implementation of this interface.
Additionally, you need to use Spring Batch provided ClassifierCompositeItemWriter.
Here is a summary of steps:
The POJO/Java Bean that is passed on to writer should have some kind of String field that can identify the target ItemWriter for that POJO.
Then you write a Classifier that returns that String type for each POJO like this:
public class UpdateOrInsertClassifier {
#Classifier
public String classify(WrittenMasterBean writtenBean){
return writtenBean.getType();
}
}
and
#Bean
public UpdateOrInsertClassifier router() {
return new UpdateOrInsertClassifier();
}
I assume that WrittenMasterBean is POJO that you sent to either of writers and it has a private String type; field This Classifier is your router.
Then you implement BackToBackPatternClassifier like -
#Bean
public Classifier classifier() {
BackToBackPatternClassifier classifier = new BackToBackPatternClassifier();
classifier.setRouterDelegate(router());
Map<String,ItemWriter<WrittenMasterBean>> writerMap = new HashMap();
writerMap.put("Writer1", writer1());
writerMap.put("Writer2", writer2());
classifier.setMatcherMap(writerMap);
return classifier;
}
i.e. I assume that keys Writer1 and Writer2 will identify your writers for that particular bean.
writer1() and writer2() return actual ItemWriter beans.
BackToBackPatternClassifier needs two fields - one router classifier and another matcher map.
Restriction is that keys are Strings in this classifier. You can't use any other type of keys.
Pass on BackToBackPatternClassifier to ClassifierCompositeItemWriter - You need to use Spring Batch provided ClassifierCompositeItemWriter
#Bean
public ItemWriter<WrittenMasterBean> classifierWriter(){
ClassifierCompositeItemWriter<WrittenMasterBean> writer = new ClassifierCompositeItemWriter();
writer.setClassifier(classifier());
return writer;
}
You configure this - classifierWriter() into your Step .
Then you are good to go.