javax.persistence.Entity : Entity « javax.persistence « Java by API

1. Java by API
2. javax.persistence
3. Entity

javax.persistence.Entity

  


File: Message.java


import java.util.Date;

import javax.persistence.Basic;
import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Message {
  @Id
  private long id = System.currentTimeMillis();

  @Basic
  private String message;

  @Basic
  private Date created = new Date();

  public Message() {
  }

  public Message(String msg) {
    message = msg;
  }

  public void setId(long val) {
    id = val;
  }

  public long getId() {
    return id;
  }

  public void setMessage(String msg) {
    message = msg;
  }

  public String getMessage() {
    return message;
  }

  public void setCreated(Date date) {
    created = date;
  }

  public Date getCreated() {
    return created;
  }
}


File: ProfessorService.java

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;

public class ProfessorService {
  protected EntityManager em;

  public ProfessorService(EntityManager em) {
    this.em = em;
  }

  public void messageCreateAndList() {
    em.persist(new Message("Hello Persistence!"));
    Query q = em.createQuery("select m from Message m");

    for (Message m : (List<Message>) q.getResultList()) {
        System.out.println(m.getMessage()
            + " (created on: " + m.getCreated() + ")"); 
    }
  }

}


File: JPAUtil.java

import java.io.Reader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class JPAUtil {
  Statement st;
  
  public JPAUtil() throws Exception{
    Class.forName("org.hsqldb.jdbcDriver");
    System.out.println("Driver Loaded.");
    String url = "jdbc:hsqldb:data/tutorial";

    Connection conn = DriverManager.getConnection(url, "sa", "");
    System.out.println("Got Connection.");
    st = conn.createStatement();
  }
  public void executeSQLCommand(String sql) throws Exception {
    st.executeUpdate(sql);
  }
  public void checkData(String sql) throws Exception {
    ResultSet rs = st.executeQuery(sql);
    ResultSetMetaData metadata = rs.getMetaData();

    for (int i = 0; i < metadata.getColumnCount(); i++) {
      System.out.print("\t"+ metadata.getColumnLabel(i + 1)); 
    }
    System.out.println("\n----------------------------------");

    while (rs.next()) {
      for (int i = 0; i < metadata.getColumnCount(); i++) {
        Object value = rs.getObject(i + 1);
        if (value == null) {
          System.out.print("\t       ");
        } else {
          System.out.print("\t"+value.toString().trim());
        }
      }
      System.out.println("");
    }
  }
}


File: Main.java

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class Main {
  public static void main(String[] a) throws Exception {
    JPAUtil util = new JPAUtil();

    EntityManagerFactory emf = Persistence.createEntityManagerFactory("ProfessorService");
    EntityManager em = emf.createEntityManager();
    ProfessorService service = new ProfessorService(em);

    em.getTransaction().begin();


    service.messageCreateAndList();
    
    util.checkData("select * from Message");

    em.getTransaction().commit();
    em.close();
    emf.close();
  }
}





File: persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0">
  <persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL">
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
      <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
      <property name="hibernate.connection.username" value="sa"/>
      <property name="hibernate.connection.password" value=""/>
      <property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
    </properties>
  </persistence-unit>
</persistence>





   
    
  

JPA-MarkAsBasic.zip( 5,332 k)

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