Spring BeanPostProcessor

The BeanPostProcessor interface defines callback methods that you can implement to provide your own instantiation logic. If we want to perform some tasks before and after initializing bean, we can do this by BeanPostProcessor.

It is a 2 step process.

Step 1: Implement BeanPostProcessor interface

Step 2: Register this bean with spring, by defining in spring.xml

We can implement multiple BeanPostProcessors and control the order of execution. In this post, i am going to explain how to implement single BeanPostProcessor, later post, i will explain, how to implement multiple BeanPostProcessors.

Step 1 : Create new maven project “spring_tuorial”. Project structure looks like below.

Step 2 : Update “pom.xml” file for maven dependencies.

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>spring_tutorial</groupId> 
 <artifactId>spring_tutorial</artifactId> 
 <version>0.0.1-SNAPSHOT</version> 
 <packaging>war</packaging> 
 <name>spring_tutorial</name> 
 <description>spring_tutorial</description> 
 <properties> 
  <org.springframework-version>4.1.5.RELEASE</org.springframework-version> 
 </properties> 

 <dependencies> 
  <dependency> 
   <groupId>org.springframework</groupId> 
   <artifactId>spring-context</artifactId> 
   <version>${org.springframework-version}</version> 
  </dependency> 

 </dependencies> 
</project>

Step 3: Create new package “com.springtutorial.model” under “src/main/java”.

Step 4: Create “Address” class under the package “com.springtutorial.model”.

package com.springtutorial.model; 

public class Address{ 
  private String street; 
  private String city; 
  private String state; 
  private String country; 
  private String pin; 

  public String getStreet() { 
    return street; 
  } 

  public void setStreet(String street) { 
    this.street = street; 
  } 

  public String getCity() { 
    return city; 
  } 

  public void setCity(String city) { 
    this.city = city; 
  } 

  public String getState() { 
    return state; 
  } 

  public void setState(String state) { 
    this.state = state; 
  } 

  public String getCountry() { 
    return country; 
  } 

  public void setCountry(String country) { 
    this.country = country; 
  } 

  public String getPin() { 
    return pin; 
  } 

  public void setPin(String pin) { 
    this.pin = pin; 
  } 

  @Override 
  public String toString() { 
    StringBuilder builder = new StringBuilder(); 
    builder.append("Address [street=").append(street).append(", city=").append(city) 
        .append(", state=").append(state).append(", country=").append(country).append(", pin=") 
        .append(pin).append("]"); 
    return builder.toString(); 
  } 

} 

Step 5: Create “Employee” class under the package “com.springtutorial.model”.

package com.springtutorial.model; 

public class Employee { 
  private String firstName; 
  private String lastName; 
  private int id; 
  private Address address; 

  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 getId() { 
    return id; 
  } 

  public void setId(int id) { 
    this.id = id; 
  } 

  public Address getAddress() { 
    return address; 
  } 

  public void setAddress(Address address) { 
    this.address = address; 
  } 

  @Override 
  public String toString() { 
    StringBuilder builder = new StringBuilder(); 
    builder.append("Employee [firstName=").append(firstName).append(", lastName=").append(lastName) 
        .append(", id=").append(id).append(", address=").append(address).append("]"); 
    return builder.toString(); 
  } 

} 

Step 6:  Create NameBeanPostProcessor class in “com.springtutorial.main” package.

package com.springtutorial.main; 

import org.springframework.beans.BeansException; 
import org.springframework.beans.factory.config.BeanPostProcessor; 

public class NameBeanPostProcessor implements BeanPostProcessor{ 

  public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { 
    System.out.println("Before initializing bean " + beanName); 
    return bean; 
  } 

  public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { 
    System.out.println("After initializing bean " + beanName); 
    return bean; 
  } 

} 

Bean post processor is created by implementing “BeanPostProcessor” interface.

postProcessAfterInitialization(Object bean, String beanName)

Method called after initialization of bean.

postProcessBeforeInitialization(Object bean, String beanName)

Method called before initialization of bean.

Step 6: Create “spring.xml” file in “src/main/resources”.

spring.xml

<?xml version="1.0" encoding="UTF-8"?> 

<beans xmlns="http://www.springframework.org/schema/beans" 
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xsi:schemaLocation="http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
  
 <bean id="employee1" class="com.springtutorial.model.Employee"> 
  <property name="firstName" value="Hari Krishna" /> 
  <property name="lastName" value="Gurram" /> 
  <property name="id" value="553" /> 
  <property name="address" ref="address"/> 
 </bean> 

 <bean id="address" class="com.springtutorial.model.Address"> 
  <property name="street" value="Chowdeswari temple" /> 
  <property name="city" value="Bangalore" /> 
  <property name="state" value="Karnataka" /> 
  <property name="country" value="India" /> 
  <property name="pin" value="560037" /> 
 </bean> 
  
 <bean class="com.springtutorial.main.NameBeanPostProcessor" /> 

</beans>

"spring.xml" is used to assign unique IDs to different beans, to control the creation of objects with different values. You have to make sure that “spring.xml” file is available in CLASSPATH and use the same name in main application while creating application context as shown in Main.java file.

Step 7 : Create package “com.springtutorial.main” under “src/main/java”.

Step 8 : Create Main class under package “com.springtutorial.main”.

package com.springtutorial.main; 

import org.springframework.context.ApplicationContext; 
import org.springframework.context.support.ClassPathXmlApplicationContext; 

import com.springtutorial.model.Employee; 
 
public class Main { 
  public static void main(String args[]) { 
    ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml"); 

    Employee emp1 = (Employee) context.getBean("employee1"); 

    System.out.println(emp1); 
    
    ((ClassPathXmlApplicationContext) context).close(); 
  } 
} 

Step 9 : Run Main.java,you will get output like below.

Mar 26, 2015 10:03:54 PM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh 
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1b7682d: startup date [Thu Mar 26 22:03:54 IST 2015]; root of context hierarchy 
Mar 26, 2015 10:03:54 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions 
INFO: Loading XML bean definitions from class path resource [spring.xml] 
Before initializing bean address 
After initializing bean address 
Before initializing bean employee1 
After initializing bean employee1 
Employee [firstName=Hari Krishna, lastName=Gurram, id=553, address=Address [street=Chowdeswari temple, city=Bangalore, state=Karnataka, country=India, pin=560037]] 
Mar 26, 2015 10:03:54 PM org.springframework.context.support.ClassPathXmlApplicationContext doClose 
INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@1b7682d: startup date [Thu Mar 26 22:03:54 IST 2015]; root of context hierarchy 

Final project structure looks like below.

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