Hibernate Session provide different methods to fetch the data (or a single record) from the database. In this tutorial, we will demonstrate the use ofSession.byId() method in Hibernate using the annotation based configuration.
 
 
 
 
 
 
 
 

1. Introduction

1.1 Hibernate

• Object-Relational Mapping or ORM is the programming technique to map application domain model objects to the relational database tables
• Hibernate is a Java-based ORM tool that provides the framework for mapping application domain objects to the relational database tables and vice versa. It provides reference implementation of Java Persistence API that makes it a great choice as an ORM tool with benefits of loose coupling
• A Framework that has an option to map plain old Java objects to the traditional database tables with the use of JPA annotations as well asXML based configuration

1.2 Hibernate Annotations

• Hibernate annotations is the newest way to define mappings without a use of aXML file
• Developers useannotations to provide metadata configuration along with the Java code. Thus, making the code easy to understand
• XML provides the ability to change the configuration without building the project. Thus, annotations are less powerful than theXML configuration and should only be used for table and column mappings
• Annotations are preconfigured with sensible default values, which reduce the amount of coding required. For e.g. Class name defaults to Table name and Field names default to Column names

1.2.1 Reference Guide on Hibernate Annotations

Hibernate Annotations are based on the JPA 2 specification. All the JPA annotations are defined in thejavax.persistence.* package. The basic JPA annotations of Hibernate that can be used in an entity are the ones below.

1.3 Hibernate Session Interface

In Hibernate, an entity (or a single record) can be obtained from the database using the followingSession interface methods:

• Session.get(): This method returns a persistence object of the given class with the given identifier. It will returnnull if there is no persistence object
• Session.load(): This method returns a persistence object of the given class with the given identifier. It will throw an exceptionObjectNotFoundException, if an entity does not exist in the database. Theload() method may return a proxy object instead of a real persistence object
• Session.byId(): This method is used to obtain a persistence object by its primary identifier

1.3.1 Session byId() Method

Hibernate’sSession interface provides one or morebyId() methods for loading the entities from the database. Theorg.hibernate.Session.byId() method returns the instance of theIdentifierLoadAccess class whose methods either accepts the ClassentityName or the StringentityName as an input parameter.

Theorg.hibernate.IdentifierLoadAccess class loads an entity from the database by using the primary identifier. Let’s look at the different flavors of the methods available with theIdentifierLoadAccess class:

• getReference(Serializable id): Here in this method developers pass the value of the primary identifier and in return they get the entity from the database, assuming the value exists in the database. If there isno value corresponding to the given identifier, themethod throws an exception
• load(Serializable id): Here in this method developers pass the value of the primary identifier and in return they get the entity from the database, assuming the value exists in the database. If there isno value corresponding to the given identifier, themethod returns a null value
• with(LockOptions options): This method returns the same value as the calling instance i.e. theIdentifierLoadAccess but with lock options, for e.g.READ,NO_WAIT,NONE etc

1.4 Download and Install Hibernate

You can readthis tutorial in order to download and install Hibernate in the Eclipse IDE.

1.5 Download and Install MySQL

You can watchthis video in order to download and install the MySQL database on your Windows operating system.

Now, open up the Eclipse IDE and let’s see how to implement theSession.byId() method in Hibernate using Annotation!

2. Hibernate Session byId Example

2.1 Tools Used

We are using Eclipse Kepler SR2, JDK 8, MySQL database and Maven. Having said that, we have tested the code against JDK 1.7 and it works well.

2.2 Project Structure

Firstly, let’s review the final project structure, in case you are confused about where you should create the corresponding files or folder later!

2.3 Project Creation

This section will demonstrate on how to create a Java-based Maven project with Eclipse. In Eclipse IDE, go toFile -> New -> Maven Project.

In the New Maven Project window, it will ask you to select project location. By default, ‘Use default workspace location’ will be selected. Select the ‘Create a simple project (skip archetype selection)’ checkbox and just click on next button to proceed.

It will ask you to ‘Enter the group and the artifact id for the project’. We will input the details as shown in the below image. The version number will be by default:0.0.1-SNAPSHOT.

Click on Finish and the creation of a maven project is completed. If you observe, it has downloaded the maven dependencies and apom.xml file will be created. It will have the following code:

pom.xml

<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>HibernateId</groupId><artifactId>HibernateId</artifactId><version>0.0.1-SNAPSHOT</version></project>

We can start adding the dependencies that developers want like Hibernate, MySQL etc. Let’s start building the application!

3. Application Building

Below are the steps involved in developing this application.

3.1 Database & Table Creation

The following MySQL script is used to create a database calledtutorialDb with table:employee. Open MySQL terminal or workbench terminal and execute theSQLscript.

CREATE DATABASE IF NOT EXISTS tutorialDb;USE tutorialDb;DROP TABLE IF EXISTS employee;CREATE TABLE employee (emp_id INT(50) NOT NULL AUTO_INCREMENT, emp_fname VARCHAR(200) DEFAULT NULL, emp_lname VARCHAR(200) DEFAULT NULL,emp_age INT(50) DEFAULT NULL,emp_education VARCHAR(200) DEFAULT NULL,emp_salary INT(100) DEFAULT NULL, PRIMARY KEY (emp_id));INSERT INTO employee (emp_id, emp_fname, emp_lname, emp_age, emp_education, emp_salary) VALUES (1, 'Harry', 'Potter', 23, 'Bachelor Of Technology', 2500);INSERT INTO employee (emp_id, emp_fname, emp_lname, emp_age, emp_education, emp_salary) VALUES (2, 'Java', 'Geek', 25, 'Master Of Technology', 6500);INSERT INTO employee (emp_id, emp_fname, emp_lname, emp_age, emp_education, emp_salary) VALUES (3, 'Daniel', 'Atlas', 32, 'Business Administration', 4500);

If everything goes well, the table will be shown in the MySQL Workbench.

3.2 Maven Dependencies

Here, we specify only two dependencies for Hibernate Core and MySQL Connector. The rest dependencies will be automatically resolved by Maven, such as Hibernate JPA and Hibernate Commons Annotations. Theupdated file will have the following code:

pom.xml

<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>HibernateId</groupId><artifactId>HibernateId</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><dependencies><!-- Hibernate 4.3.6 Final --><dependency><groupId>org.hibernate</groupId><artifactId>hibernate-core</artifactId><version>4.3.6.Final</version></dependency><!-- Mysql Connector --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.21</version></dependency></dependencies><build><finalName>${project.artifactId}</finalName></build></project>

3.3 Java Class Creation

Let’s create the required Java files. Right-click onsrc/main/java folder,New -> Package.

A new pop window will open where we will enter the package name as:com.jcg.hibernate.id.

Once the package is created in the application, we will need to create the model and the implementation classes. Right-click on the newly created package:New -> Class.

A new pop window will open and enter the file name as:Employee. The model class will be created inside the package:com.jcg.hibernate.id.

Repeat the step (i.e. Fig. 9) and enter the filename as:AppMain. The implementation class will be created inside the package:com.jcg.hibernate.id.

3.3.1 Implementation of Model Class

This class is used to map the model attributes with theSQL column names. Add the following code to it:

Employee.java

package com.jcg.hibernate.id;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name="employee")public class Employee {@Id@Column(name = "emp_id")@GeneratedValue(strategy = GenerationType.AUTO)private int employeeId;@Column(name = "emp_fname")private String firstName;@Column(name = "emp_lname")private String lastName;@Column(name = "emp_age")private int age;@Column(name = "emp_education")private String education;@Column(name = "emp_salary")private int salary;public int getEmployeeId() {return employeeId;}public void setEmployeeId(int employeeId) {this.employeeId = employeeId;}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 int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getEducation() {return education;}public void setEducation(String education) {this.education = education;}public int getSalary() {return salary;}public void setSalary(int salary) {this.salary = salary;}public String toString() {return "Id: " + employeeId + ", Name: " + firstName + " " + lastName + ", Age: " + age + ", Education: " + education + ", Salary:" + salary + "$\n";}}

3.3.2 Implementation of Utility Class

This class helps in creating theSessionFactory object from the Hibernate configuration file and interacts with the database to perform theSELECT operation. Add the following code to it:

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AppMain.java

package com.jcg.hibernate.id;import org.hibernate.IdentifierLoadAccess;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;public class AppMain {static Session sessionObj;static SessionFactory sessionFactoryObj;static IdentifierLoadAccess identifierObj;// This Method Is Used To Create The Hibernate's SessionFactory Objectprivate static SessionFactory buildSessionFactory() {// Creating Configuration Instance & Passing Hibernate Configuration File.Configuration configObj = new Configuration();configObj.configure("hibernate.cfg.xml");// Since Hibernate Version 4.x, ServiceRegistry Is Being Used.ServiceRegistry serviceRegistryObj = new StandardServiceRegistryBuilder().applySettings(configObj.getProperties()).build(); // Creating Hibernate SessionFactory Instance.sessionFactoryObj = configObj.buildSessionFactory(serviceRegistryObj);return sessionFactoryObj;}// This Method Is Used To Display The Records From The Database Table (i.e. Assuming The Records Are Already Present In The Database Table)public static void displayRecords() {Employee empObj;// Opening The Hibernate's Session Object To Start The Database Transactions.sessionObj = buildSessionFactory().openSession();identifierObj = sessionObj.byId(Employee.class);// Accessing The Employee Details For The Existing Identifier Using The 'getReference()' Method.int emp_id1 = 1;empObj = (Employee)identifierObj.getReference(new Integer(emp_id1));if(empObj != null) {System.out.println(empObj.toString());}// Accessing The Employee Details For The Existing Identifier Using The 'load()' Method.int emp_id2 = 3;empObj = (Employee)identifierObj.load(new Integer(emp_id2));if(empObj != null) {System.out.println(empObj.toString());}// Accessing The Employee Details For The Non-Existing Identifier Using The 'load()' Method. This Will Return 'null'.int emp_id3 = 5;empObj = (Employee)identifierObj.load(new Integer(emp_id3));if(empObj != null) {System.out.println(empObj.toString());} else {System.out.println(empObj);}// Accessing The Employee Details For The Non-Existing Identifier Using The 'getReference()' Method. This Will Return 'ObjectNotFoundException'.int emp_id4 = 7;empObj = (Employee)identifierObj.getReference(new Integer(emp_id4));if(empObj != null) {System.out.println(empObj.toString());} else {System.out.println("\n"+empObj);}// Closing The Hibernate's Session Object To Close The Database Transactions.sessionObj.close();}public static void main(String[] args) {displayRecords();}}

3.4. Hibernate Configuration File

To configure the Hibernate framework, we need to implement a configuration file i.e.hiberncate.cfg.xml. Right-click onsrc/main/resources folder,New -> Other.

A new pop window will open and select the wizard as anXML file.

Again, a pop-up window will open. Verify the parent folder location asHibernateId/src/main/resources and enter the file name as:hibernate.cfg.xml. Click Finish.

Once the file is created, we will include the database configuration and the mapping class details. Add the following code to it:

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE hibernate-configuration PUBLIC        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration><session-factory><!-- SQL Dialect --><property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property><!-- Database Connection Settings --><property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property><property name="hibernate.connection.url">jdbc:mysql://localhost:3306/tutorialDb</property><property name="hibernate.connection.username">root</property><property name="hibernate.connection.password"></property><!-- Echo All Executed SQL To Console --><property name="show_sql">true</property><!-- Specifying Session Context --><property name="hibernate.current_session_context_class">org.hibernate.context.internal.ThreadLocalSessionContext</property><!-- Mapping With Model Class Containing Annotations --><mapping /></session-factory></hibernate-configuration>

Let’s look at some basic details:

• Here, we instructed Hibernate to connect to a MySQL database namedtutorialDb and the Mapping classes to be loaded
• We have also instructed Hibernate framework to useMySQLDialect i.e. Hibernate will optimize the generated SQL statements for MySQL
• This configuration will be used to create a HibernateSessionFactory object
• show_sql tag will instruct the Hibernate framework to log all theSQL statements on the console

4. Run the Application

To run the Hibernate application, Right-click on theAppMain class-> Run As -> Java Application. Developers can debug the example and see what happens after every step!

5. Project Demo

In the above code, we have used theSession.byId() method to retrieve the Employees with employee id as:1 and3. Hibernate returns the entity (or the record) from the database.

While in the case of employee id as:5 and7, Hibernate returns anull value in case ofidentifierObj.load() operation or throws aObjectNotFoundException exception in case ofidentifierObj.getReference() operation.

That’s all for this post. Happy Learning!!

6. Conclusion

This tutorial uses a simple example to illustrate the functionality of theSession.byId() method in the Hibernate framework and helps developers understand the basic configuration required to achieve this. That’s all for HibernatebyId tutorial and I hope this article served you whatever you were looking for.

7. Download the Eclipse Project

This was an example of Hibernate byId.

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