Differences between load() and get() method is one of the most popular interview question in hibernate. Irrespective of experience or fresher, every person will face this question in telephonic or face to face interview.
Not only the interview point of view, in order to understanding the internals of hibernate everybody should aware of the differences between load() and get() methods.
Hibernate load() and get() :
In order to get the details from the database in hibernate, we can call either load() or get() method. By using the load() or get() method we can load (read) the data from the database.
The load and get methods are both looking like a same, and also these two are generates same output. But the functionality wise there are few differences in internally.
In this tutorial we will discuss all possible differences between load() and get() methods with examples.
differences between load() and get()
Before going to discuss about the differences directly, It is mandatory to know what exactly are the load and get methods and how they are working internally.
How load() method works ?
In order to get the details from the database, we can use the load() method. The load is a instance method which is coming from the hibernate Session object. We can call the load() with two parameters.
- session.load(Class class, Serializable id);
- session.load(String classname, Serializable id);
By using the above two methods we can load the data from the database. When ever the load() method is called, the hibernate creates a proxy object of a POJO class (provided as parameter), and it will set the id to the proxy object, then it returns the proxy object to the program. Based on the operations performed on the proxy object, the hibernate will decide whether to go cache or database to load the data. This process is called lazy loading. When we access non-id property (not a primary key) of proxy object then hibernate first goes to first level cache and if that object doesn’t available in the cache then hibernate goes to database for loading an object.
session.load() flow diagram :
Example: Student.java
package com.onlinetutorialspoint.pojo;
public class Student implements java.io.Serializable {
private Integer id;
private String name;
private Integer rollNumber;
public Student() {
}
public Student(Integer id, String name, Integer rollNumber) {
this.id = id;
this.name = name;
this.rollNumber = rollNumber;
}
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public Integer getRollNumber() {
return this.rollNumber;
}
public void setRollNumber(Integer rollNumber) {
this.rollNumber = rollNumber;
}
}
Creating Mapping File Student.hbm.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Jun 10, 2015 11:42:29 AM by Hibernate Tools 3.6.0 -->
<hibernate-mapping>
<class catalog="onlinetutorialspoint" name="com.onlinetutorialspoint.pojo.Student" table="student">
<id name="id" type="java.lang.Integer">
<column name="id"/>
<generator class="identity"/>
</id>
<property name="name" type="string">
<column length="50" name="name"/>
</property>
<property name="rollNumber" type="java.lang.Integer">
<column name="rollnumber"/>
</property>
</class>
</hibernate-mapping>
Create a Main class DbOperations.java
package com.onlinetutorialspoint.service;
import com.onlinetutorialspoint.pojo.Student;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class DbOperations {
public static void main(String[] args) {
Configuration configuration = new Configuration();
configuration.configure("hibernate.cfg.xml");
SessionFactory factory = configuration.buildSessionFactory();
Session session = factory.openSession();
Object o = session.load(Student.class, 101);
Student s = (Student) o;
// For getting the Id property hibernate will not go to Cache or Database.
// It will take from the Proxy.
System.out.println("StudentId : " + s.getId());
// As name is a non-id property, hibernate first checks in cache,
// If the value doesn't found in the cache then it will go to data base and fetch the values
System.out.println("Student Name : " + s.getName());
}
}
Output :
If we observe the output, after printing the StudentId (Id Property) hibernate insert statements will be executed. Hence while loading the load() method hibernate will create the proxy object and assigned id to that proxy.
When ever we ask for id property it will take from the proxy only, this process is called as lazy loading. If we ask for non-id properties, then it will goto first level of cache or Database. If the corresponding Object is not found in the database, it returns (load() method) ObjectNotFoundException. Example :
package com.onlinetutorialspoint.service;
import com.onlinetutorialspoint.pojo.Student;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class DbOperations {
public static void main(String[] args) {
Configuration configuration = new Configuration();
configuration.configure("hibernate.cfg.xml");
SessionFactory factory = configuration.buildSessionFactory();
Session session = factory.openSession();
Object o = session.load(Student.class, 102);
Student s = (Student) o;
// For getting the Id property hibernate will not go to Cache or Database.
// It will take from the Proxy.
System.out.println("StudentId : " + s.getId());
// As name is a non-id property, hibernate first checks in cache,
// If the value doesn't found in the cache then it will go to data base and fetch the values, If // it doesn't exist even in database throws ObjectNotFoundException
System.out.println("Student Name : " + s.getName());
}
}
Output :
How get() method works ?
Like wise load() method, in order to get the details from the database we can use the get() method as well. We can call the get() method with two parameters.
- session.get(Class class,Serializable id);
- session.get(String className,Serializable id);
When we call the get() method, then hibernate first goes to first level cache and if that object doesn’t exist in the first level cache then it goes to database and loads the object from database. If Id doesn’t exist in the database, then get() method returns null. When get() method is called no proxy object is created, hence it is called as early loading.
session.get() method flow diagram :
Example :
package com.onlinetutorialspoint.service;
import com.onlinetutorialspoint.pojo.Student;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class DbOperations {
public static void main(String[] args) {
Configuration configuration = new Configuration();
configuration.configure("hibernate.cfg.xml");
SessionFactory factory = configuration.buildSessionFactory();
Session session = factory.openSession();
Object o = session.get(Student.class, 101);
}
}
Output :
On the above example, we didn’t do any operations on the “o”. We didn’t even type cast it, but the hibernate directly went to database and get the details from the database and stored the details in first level cache.
If we use the object “o” the details are getting from the cache.
Example :
package com.onlinetutorialspoint.service;
import com.onlinetutorialspoint.pojo.Student;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class DbOperations {
public static void main(String[] args) {
Configuration configuration = new Configuration();
configuration.configure("hibernate.cfg.xml");
SessionFactory factory = configuration.buildSessionFactory();
Session session = factory.openSession();
Object o = session.get(Student.class, 101);
Student student = (Student) o;
System.out.println("Student Id : " + student.getId());
System.out.println("Student Name : " + student.getName());
System.out.println("Student rollNumber : " + student.getRollNumber());
}
}
Output :
Differences between load() and get() methods :
- When calling the load() method hibernate creates an proxy object and returns the proxy object, but in the case of get() method there is no concept called proxy it directly hit the database.
- load() method loads an object lazily, where as get() method loads an object early.
- performance point of view load() method is recommended when compared to get() method.
- If the given id doesn’t exist the load() method throws ObjectNotFoundException, where as get() methods returns null.
Happy Learning 🙂
