Java Technologies: get persistence operation in hibernate

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Does it include associations in select query which are configured for lazy loading or null value is set for such associations in returned object?

1) The session.get() will NOT initiate lazy stuff. NEVER. In fact that is the central thought of the design. Otherwise - we would be able to load whole DB in one SHOT (in one JAVA call to session.get())

2) And also there WILL NOT be null instead. Each reference or collection will be represented by proxy. This is the way how we can avoid to load compelte DB in one shot (all stuff initialized with one method get). Because each proxy is in fact a promise - once we will touch it... it will load the real data.

And so on. So get is very safe way how to recieve as few data as was configured....

get

Object get(Class clazz,
           Serializable id)
           throws HibernateException

Return the persistent instance of the given entity class with the given identifier, or null if there is no such persistent instance. (If the instance is already associated with the session, return that instance. This method never returns an uninitialized instance.)

Parameters:: clazz - a persistent class; id - an identifier
Returns:: a persistent instance or null
Throws:: HibernateException

get

Object get(Class clazz,
           Serializable id,
           LockMode lockMode)
           throws HibernateException

Deprecated. LockMode parameter should be replaced with LockOptions

Parameters:: clazz - a persistent class; id - an identifier; lockMode - the lock mode
Returns:: a persistent instance or null
Throws:: HibernateException

get

Object get(Class clazz,
           Serializable id,
           LockOptions lockOptions)
           throws HibernateException

Parameters:: clazz - a persistent class; id - an identifier; lockOptions - the lock mode
Returns:: a persistent instance or null
Throws:: HibernateException

get

Object get(String entityName,
           Serializable id)
           throws HibernateException

Return the persistent instance of the given named entity with the given identifier, or null if there is no such persistent instance. (If the instance is already associated with the session, return that instance. This method never returns an uninitialized instance.)

Parameters:: entityName - the entity name; id - an identifier
Returns:: a persistent instance or null
Throws:: HibernateException

get

Object get(String entityName,
           Serializable id,
           LockMode lockMode)
           throws HibernateException

Deprecated. LockMode parameter should be replaced with LockOptions

Parameters:: entityName - the entity name; id - an identifier; lockMode - the lock mode
Returns:: a persistent instance or null
Throws:: HibernateException

get

Object get(String entityName,
           Serializable id,
           LockOptions lockOptions)
           throws HibernateException

Parameters:: entityName - the entity name; id - an identifier; lockOptions - contains the lock mode
Returns:: a persistent instance or null
Throws:: HibernateException

Here is the example code to test get() method functionality :

This is hibernate.cfg.xml file for connecting the postgreSQL database.

 <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
   <!-- <session-factory> <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property> 
		hibernate word is optional <property name="connection.url">jdbc:oracle:thin:@localhost:1521:ORCL</property> 
		<property name="hibernate.connection.username">kcv</property> <property name="hibernate.connection.password">kcv</property> 
		<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property> 
		<property name="show_sql">true</property> <mapping resource="Employee.hbm.xml"/> 
		</session-factory> -->
   <session-factory>
      <property name="hibernate.current_session_context_class">thread</property>
      <property name="hbm2ddl.auto">create</property>
      <property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
      <property name="connection.url">jdbc:postgresql://localhost:5432/hibernate</property>
      <property name="connection.username">postgres</property>
      <property name="connection.password">password</property>
      <property name="connection.driver_class">org.postgresql.Driver</property>
      <property name="show_sql">true</property>
      <property name="format_sql">true</property>
      <property name="use_sql_comments">true</property>
      		<mapping resource="EmployeeBean.hbm.xml" />
   </session-factory>
</hibernate-configuration>

This is EmployeeBean.hbm.xml mapping file for map the Entity(POJO) class to columns.

 <?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.cv.hibernate.model.EmployeeBean"
		table="EMPLOYEE_GET">
		<id name="id" column="EID"  type="java.lang.Long">
		</id>
		<property name="firstName" type="java.lang.String">
			<column name="FIRSTNAME" length="29" not-null="true" />
		</property>
		<property name="lastName" type="java.lang.String">
			<column name="LASTNAME" length="29" not-null="true" />
		</property>
		<property name="email" type="java.lang.String">
			<column name="EMAIL" length="39" not-null="true" />
		</property>
	</class>
</hibernate-mapping>

This is Get.java main class having the application business logic.

 
    
package com.cv.hibernate;



import org.apache.log4j.Logger;

import org.hibernate.Session;



import com.cv.hibernate.model.EmployeeBean;

import com.cv.hibernate.util.HibernateUtil;



/** @author Chandra Vardhan */



public class Get {



  private final static Logger logger = Logger.getLogger(Get.class);



  public static void main(String args[]) throws Exception {

    HibernateUtil.saveOrUpdate();

    Session session = HibernateUtil.getSession();

    EmployeeBean eb = (EmployeeBean) session.get(EmployeeBean.class,

        new Long(101));

    

    logger.info("get is called... observe that hibernate select query already generated before this line...");

    logger.info("Id of the Employee : "+eb.getId());

    logger.info(eb.getFirstName() + " " + eb.getLastName() + " "

        + eb.getEmail());

    HibernateUtil.closeSession();



  }

}

This is EmployeeBean.java Entity(POJO) class having the fields needs to be configured in mapping file.

 
    
package com.cv.hibernate.model;



/**

 * @author Chandra Vardhan

 */

public class EmployeeBean {

  private long id;

  private String firstName;

  private String lastName;

  private String email;



  public long getId() {

    return id;

  }



  public void setId(long id) {

    this.id = id;

  }



  public String getFirstName() {

    return firstName;

  }



  public void setFirstName(String firstName) {

    this.firstName = firstName;

  }



  public String getLastName() {

    return lastName;

  }



  public void setLastName(String lastName) {

    this.lastName = lastName;

  }



  public String getEmail() {

    return email;

  }



  public void setEmail(String email) {

    this.email = email;

  }



}

This is HibernateUtil.java utility class for getting the database connection.

 
    
package com.cv.hibernate.util;



import org.apache.log4j.Logger;

import org.hibernate.HibernateException;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

import org.hibernate.cfg.Configuration;



import com.cv.hibernate.model.EmployeeBean;



/**

 * @author Chandra Vardhan

 */

/**

 * Configures and provides access to Hibernate sessions, tied to the current

 * thread of execution. Follows the Thread Local Session pattern, see

 * {@link http://hibernate.org/42.html }.

 */

public class HibernateUtil {

  private final static Logger logger = Logger.getLogger(HibernateUtil.class);



  /**

   * Location of hibernate.cfg.xml file. Location should be on the classpath

   * as Hibernate uses #resourceAsStream style lookup for its configuration

   * file. The default classpath location of the hibernate config file is in

   * the default package. Use #setConfigFile() to update the location of the

   * configuration file for the current session.

   */

  private static String CONFIG_FILE_LOCATION = "hibernate.cfg.xml";

  private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();

  private static Configuration configuration = new Configuration();

  private static SessionFactory sessionFactory;



  static {

    try {

      configuration = configuration.configure(CONFIG_FILE_LOCATION);

      StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder()

          .applySettings(configuration.getProperties());

      sessionFactory = configuration.buildSessionFactory(builder.build());

      logger.info("%%%% Connection successful %%%%");

    } catch (Exception e) {

      logger.error("%%%% Error Creating SessionFactory %%%%");

      e.printStackTrace();

    }

  }



  private HibernateUtil() {

  }



  /**

   * Returns the ThreadLocal Session instance. Lazy initialize the

   * <code>SessionFactory</code> if needed.

   * 

   * @return Session

   * @throws HibernateException

   */

  public static Session getSession() throws HibernateException {

    Session session = (Session) threadLocal.get();



    if (session == null || !session.isOpen()) {

      if (sessionFactory == null) {

        rebuildSessionFactory();

      }

      session = (sessionFactory != null) ? sessionFactory.openSession()

          : null;

      threadLocal.set(session);

    }



    return session;

  }



  /**

   * Rebuild hibernate session factory

   * 

   */

  public static void rebuildSessionFactory() {

    try {

      configuration = configuration.configure(CONFIG_FILE_LOCATION);

      StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder()

          .applySettings(configuration.getProperties());

      sessionFactory = configuration.buildSessionFactory(builder.build());

      logger.info("%%%% Connection successful %%%%");

    } catch (Exception e) {

      logger.error("%%%% Error Creating SessionFactory %%%%");

      e.printStackTrace();

    }

  }



  /**

   * Close the single hibernate session instance.

   * 

   * @throws HibernateException

   */

  public static void closeSession() throws HibernateException {

    Session session = (Session) threadLocal.get();

    threadLocal.set(null);



    if (session != null) {

      session.close();

      System.exit(0);

    }

  }



  /**

   * return session factory

   * 

   */

  public static SessionFactory getSessionFactory() {

    return sessionFactory;

  }



  /**

   * return hibernate configuration

   * 

   */

  public static Configuration getConfiguration() {

    return configuration;

  }



  public static void saveOrUpdate() {

    Session session = getSession();

    EmployeeBean eb = new EmployeeBean();

    eb.setId(new Long(101));

    eb.setFirstName("chandra");

    eb.setLastName("vardhan");

    eb.setEmail("meetkodam@gmail.com");

    session.beginTransaction();

    session.saveOrUpdate(eb);

    logger.info("Saved successful...");

    session.getTransaction().commit();

    session.close();

  }

}

This is log4j.properties file having the entries for logging the information into the console/file.

#By default enabling Console appender

# Root logger option

log4j.rootLogger=INFO, stdout

# Redirect log messages to console

log4j.appender.stdout=org.apache.log4j.ConsoleAppender

log4j.appender.stdout.Target=System.out

log4j.appender.stdout.layout=org.apache.log4j.PatternLayout

log4j.appender.stdout.layout.ConversionPattern=%-5p [%c]:%L -->> %m%n

# Redirect log messages to a log file

#log4j.appender.file=org.apache.log4j.RollingFileAppender

#log4j.appender.file.File=C:\\servlet-application.log

#log4j.appender.file.MaxFileSize=5MB

#log4j.appender.file.MaxBackupIndex=10

#log4j.appender.file.layout=org.apache.log4j.PatternLayout

#log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

This is pom.xml file having the entries of dependency jars and information to build the application .

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.cv.hb</groupId>
  <artifactId>All_operations</artifactId>
  <version>1.0</version>
 
	<dependencies>
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-entitymanager</artifactId>
			<version>4.3.5.Final</version>
		</dependency>
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-c3p0</artifactId>
			<version>4.3.5.Final</version>
		</dependency>

		<dependency>
			<artifactId>hibernate-core</artifactId>
			<groupId>org.hibernate</groupId>
			<version>4.3.5.Final</version>
		</dependency>

		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-validator</artifactId>
			<version>4.2.0.Final</version>
		</dependency>
		<dependency>
			<groupId>org.hibernate.common</groupId>
			<artifactId>hibernate-commons-annotations</artifactId>
			<version>4.0.4.Final</version>
		</dependency>
		<dependency>
			<groupId>org.hibernate.javax.persistence</groupId>
			<artifactId>hibernate-jpa-2.0-api</artifactId>
			<version>1.0.1.Final</version>
		</dependency>

		<dependency>
			<groupId>javax.validation</groupId>
			<artifactId>validation-api</artifactId>
			<version>1.0.0.GA</version>
			provided
		</dependency>
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-api</artifactId>
			<version>1.6.4</version>
		</dependency>
		<dependency>
			<groupId>org.jboss.logging</groupId>
			<artifactId>jboss-logging</artifactId>
			<version>3.1.0.CR2</version>
		</dependency>
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-log4j12</artifactId>
			<version>1.6.4</version>
		</dependency>
		<dependency>
			<groupId>postgresql</groupId>
			<artifactId>postgresql</artifactId>
			<version>9.1-901.jdbc4</version>
		</dependency>
		
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-simple</artifactId>
			<version>1.7.5</version>
		</dependency>
	</dependencies>
	<build>

		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.3</version>
				<configuration>
					<source>1.8</source>
					<target>1.8</target>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

Java Technologies

get persistence operation in hibernate