How to do it...

Perform the following steps to complete this recipe:

1. First, we need to define our persistence unit:

  <persistence-unit name="ch02-batch-pu" >
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <jta-data-source>java:app/userDb</jta-data-source>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties>
      <property name="javax.persistence.schema- 
       generation.database.action" 
       value="create"/>
      <property name="hibernate.transaction.jta.platform" 
       value="org.hibernate.service.jta.platform
       .internal.SunOneJtaPlatform"/>
    </properties>
  </persistence-unit>

2. Then, we need to declare a User entity:

@Entity
@Table(name = "UserTab")
public class User implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @NotNull
    private Integer id;

    private String name;

    private String email;

    public User() {
    }

    //DO NOT FORGET TO IMPLEMENT THE GETTERS AND SETTERS
}

3. Here, we're creating a job reader:

@Named
@Dependent
public class UserReader extends AbstractItemReader {

    private BufferedReader br;

    @Override
    public void open(Serializable checkpoint) throws Exception {
        br = new BufferedReader(
                new InputStreamReader(
                        Thread.currentThread()
                        .getContextClassLoader()
                        .getResourceAsStream
                        ("META-INF/user.txt")));
    }

    @Override
    public String readItem() {
        String line = null;

        try {
            line = br.readLine();
        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        }

        return line;
    }
}

4. Then, we need to create a job processor:

@Named
@Dependent
public class UserProcessor implements ItemProcessor {

    @Override
    public User processItem(Object line) {
        User user = new User();

        StringTokenizer tokens = new StringTokenizer((String)
        line, ",");
        user.setId(Integer.parseInt(tokens.nextToken()));
        user.setName(tokens.nextToken());
        user.setEmail(tokens.nextToken());
        
        return user;
    }
}

5. Here, we're creating a job writer:

@Named
@Dependent
public class UserWriter extends AbstractItemWriter {

    @PersistenceContext
    EntityManager entityManager;

    @Override
    @Transactional
    public void writeItems(List list) {
        for (User user : (List<User>) list) {
            entityManager.persist(user);
        }
    }
}

6. The processor, reader, and writer are referenced by the acess-user.xml file, which is located at META-INF.batch-jobs:

<?xml version="1.0" encoding="windows-1252"?>
<job id="userAccess" 
     xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
     version="1.0">
    <step id="loadData">
        <chunk item-count="3">
            <reader ref="userReader"/>
            <processor ref="userProcessor"/>
            <writer ref="userWriter"/>
        </chunk>
    </step>
</job>

7. And finally, we create a bean to interact with the batch engine:

@Named
@RequestScoped
public class UserBean {

    @PersistenceContext
    EntityManager entityManager;

    public void run() {
        try {
            JobOperator job = BatchRuntime.getJobOperator();
            long jobId = job.start("acess-user", new Properties());
            System.out.println("Job started: " + jobId);
        } catch (JobStartException ex) {
            System.out.println(ex.getMessage());
        }
    }

    public List<User> get() {
        return entityManager
                .createQuery("SELECT u FROM User as u", User.class)
                .getResultList();
    }
}

8. For the purpose of this example, we are going to use a JSF page to run the job and load the data:

 <h:body>
 <h:form>
 <h:outputLabel value="#{userBean.get()}" />
 <br />
 <h:commandButton value="Run" action="index" actionListener="#{userBean.run()}"/>
 <h:commandButton value="Reload" action="index"/>
 </h:form>
 </h:body>

Run it on a Jakarta EE server to load the web page. Click on the Run button and then the Reload button.