How to process multiple lines with the Spring Batch?

Question

My data is like this

UserId,UserData

1,data11
1,data12
2,data21
3,data31

The question is, how I can make the spring batch itemreader read multiple lines and map to object like

Map < userid, List < userdata > >

Answer 1

Steps to follow:

• create a custom Item Writer class by implementing ItemWriter where we have implemented a logic to store User object in Map<String,List<String>> because a single user can have multiple associated data

  package com.spring.batch.domain;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.springframework.batch.item.ItemWriter;
  
  public class UserItemWriter implements ItemWriter<User> {
  
      private static Map<String, List<String>> userMap = new HashMap<String, List<String>>();
  
      public void write(List<? extends User> users) throws Exception {
  
          for (User user : users) {
              List<String> list = userMap.get(user.getUserId());
              if (list == null) {
                  list = new ArrayList<String>();
              }
              list.add(user.getUserData());
              userMap.put(user.getUserId(), list);
          }
      }
  
      public static Map<String, List<String>> getUserMap() {
          return userMap;
      }
  
  }
  

• Plain User POJO class having two fieldsuserId anduserData

  package com.spring.batch.domain;
  
  public class User {
      private String userId;
      private String userData;
  
      public String getUserId() {
          return userId;
      }
  
      public void setUserId(String userId) {
          this.userId = userId;
      }
  
      public String getUserData() {
          return userData;
      }
  
      public void setUserData(String userData) {
          this.userData = userData;
      }
  
  }
  

• Main class to run the job

  package com.spring.batch.main;
  
  import java.util.List;
  import java.util.Map;
  
  import org.springframework.batch.core.Job;
  import org.springframework.batch.core.JobParametersBuilder;
  import org.springframework.batch.core.JobParametersInvalidException;
  import org.springframework.batch.core.launch.JobLauncher;
  import org.springframework.batch.core.repository.JobExecutionAlreadyRunningException;
  import org.springframework.batch.core.repository.JobInstanceAlreadyCompleteException;
  import org.springframework.batch.core.repository.JobRestartException;
  import org.springframework.beans.BeansException;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.support.ClassPathXmlApplicationContext;
  
  import com.spring.batch.domain.UserItemWriter;
  
  public class Main {
      public static void main(String[] args) throws BeansException,
              JobExecutionAlreadyRunningException, JobRestartException,
              JobInstanceAlreadyCompleteException, JobParametersInvalidException {
          ApplicationContext appContext = new ClassPathXmlApplicationContext(
                  "config/application-context.xml");
          JobLauncher jobLauncher = (JobLauncher) appContext.getBean("jobLauncher");
          jobLauncher.run(
                  (Job) appContext.getBean("job"),
                  new JobParametersBuilder().addString("input.file.name",
                          "file:src/main/resources/data/input.csv").toJobParameters());
  
          Map<String,List<String>> userMap=UserItemWriter.getUserMap();
          for (String userId : userMap.keySet()) {
              System.out.println(userId + ":" + userMap.get(userId));
          }
      }
  }
  

• application-context.xml:

  <?xml version="1.0" encoding="UTF-8"?>
  <beans ...>
  
      <import resource="jobs.xml" />
  
      <bean id="jobLauncher"
          class="org.springframework.batch.core.launch.support.SimpleJobLauncher">
          <property name="jobRepository" ref="jobRepository" />
      </bean>
  
      <bean id="jobRepository"
          class="org.springframework.batch.core.repository.support.MapJobRepositoryFactoryBean">
          <property name="transactionManager" ref="transactionManager" />
      </bean>
  
      <bean id="transactionManager"
          class="org.springframework.batch.support.transaction.ResourcelessTransactionManager" />
  
  </beans>
  

• jobs.xml

  <?xml version="1.0" encoding="UTF-8"?>
  <beans ...>
  
      <job id="job" restartable="false"
          xmlns="http://www.springframework.org/schema/batch">
          <step id="step1">
              <tasklet>
                  <chunk reader="csvItemReader" writer="userItemWriter"
                      commit-interval="2">
                  </chunk>
              </tasklet>
          </step>
      </job>
  
      <bean id="userItemWriter" class="com.spring.batch.domain.UserItemWriter"
          scope="step" />
  
      <bean id="csvItemReader" class="org.springframework.batch.item.file.FlatFileItemReader"
          scope="step">
          <property name="lineMapper">
              <bean class="org.springframework.batch.item.file.mapping.DefaultLineMapper">
                  <property name="lineTokenizer">
                      <bean
                          class="org.springframework.batch.item.file.transform.DelimitedLineTokenizer">
                          <property name="names" value="userId,userData" />
                      </bean>
                  </property>
                  <property name="fieldSetMapper">
                      <bean
                          class="org.springframework.batch.item.file.mapping.BeanWrapperFieldSetMapper">
                          <property name="prototypeBeanName" value="user" />
                      </bean>
                  </property>
              </bean>
          </property>
          <property name="linesToSkip" value="1" />
          <property name="resource" value="#{jobParameters['input.file.name']}" />
      </bean>
  
      <bean id="user" class="com.spring.batch.domain.User" scope="prototype" />
  
  </beans>
  

• input.csv

  UserId,UserData
  1,data11
  1,data12
  2,data21
  3,data31
  

• Project structure screenshot (Maven)