Spring-Batch Multi-line record Item Writer with variable number of lines per record

Question

I have the below requirement but am not able to decide on the approach to take:

I need to write data to a fixed format out put file where each record spans over mult

Answer 1

you can do it in CustomExtractor.

for Example:

     public Object[] extract(T item) {
        List<Object> values = new ArrayList<Object>();

        BeanWrapper bw = new BeanWrapperImpl(item);
        for (String propertyName : this.names) {
            values.add( bw.getPropertyValue(propertyName) + "\r\n");
        }
        return values.toArray();
    }

Answer 2

there is a multiline records writer example in the official spring-batch-samples, search for multiline.xml and MultiLineTradeItemWriter

its basically the usual delegate principle, you just need a proper domain object with supposable a list of those 1..n intermediate lines

    public class MultiLineTradeItemWriter implements ItemWriter<Trade>, ItemStream {

    private FlatFileItemWriter<String> delegate;

    public void write(List<? extends Trade> items) throws Exception {
                List<String> lines = new ArrayList<String>();
              for (Trade t : items) {
              lines.add("BEGIN");
              lines.add("INFO," + t.getIsin() + "," + t.getCustomer());
              lines.add("AMNT," + t.getQuantity() + "," + t.getPrice());
              lines.add("END");
            }
            this.delegate.write(lines);
     }
    }

Answer 3

I had a similar problem writing multiple rows to a database. Because the job step will create a List of your items, how can you return a List from the processer to the writer? That would create a List of Lists, and the doWrite method in the Writer is not set up to handle that scenario.

I am using the 1.2.0 spring-boot-starter-parent (which gives me spring-core 4.1.3) along with hibernate (4.3.7), In my case I have 'receivables', and for every 1 receivable that I read from a csv file, I then might need to update or insert many receivables into my table. I am also using HibernateItemWriter.

My solution was to extend the HibernateItemWriter. The sessionFactory field is private, so I am passing it via the constructor and also using the setter (to accomadate the existing code). So my original code (which works fine for a single 'receivable') originally looked like this:

    @Bean
    public ItemWriter<Receivable> recivableWriter() {
        HibernateItemWriter<Receivable> hibernateItemWriter = new HibernateItemWriter<Receivable>(){{ setSessionFactory(sessionFactory); }};
        return hibernateItemWriter;
    }

After extending the HibernateItemWriter, and modifying my processor to return a List, my code changed to:

    @Bean
    public ItemWriter<List<Receivable>> receivableWriter() {
        HibernateListItemWriter<List<Receivable>> hibernateItemWriter = new HibernateListItemWriter<List<Receivable>>(this.sessionFactory){{ setSessionFactory(sessionFactory); }};
        return hibernateItemWriter;
    }

And my extended class looks like this (I might clean it up but this is my initial pass. I also wish the sessionFactory and clearSession fields were not private)

package com.work;

import java.util.ArrayList;
import java.util.List;

import org.hibernate.SessionFactory;

public class HibernateListItemWriter<Receivable> extends org.springframework.batch.item.database.HibernateItemWriter<Receivable> {

    public HibernateListItemWriter(SessionFactory sessionFactory) {
        super();
        this.sessionFactory = sessionFactory;
    }

    private SessionFactory sessionFactory; 
    private boolean clearSession = true;

    @Override
    public void write(List items) {
        List<Receivable> unwrappedItems = new ArrayList<Receivable>();
        List<List<Receivable>> wrappedItems = (List<List<Receivable>>)items;
        for (List<Receivable> singleList: wrappedItems) {
            unwrappedItems.addAll(singleList);
        }
        doWrite(sessionFactory, unwrappedItems);
        sessionFactory.getCurrentSession().flush();
        if(clearSession) {
            sessionFactory.getCurrentSession().clear();
        }
    }

}

Big shout out to grepcode.com for making life easier.