Spring Bean definition inheritance

Just like one class inherit other class, we can configure bean to inherit properties from other bean. A child bean can inherit its parent bean configurations, properties.. In additional, the child beans are allow to override the inherited properies.

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 “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="commonEmployee" class="com.springtutorial.model.Employee"> 
  <property name="address" ref="address" /> 
 </bean> 
  
 <bean id="employee1" class="com.springtutorial.model.Employee" parent="commonEmployee"> 
  <property name="firstName" value="Hari Krishna" /> 
  <property name="lastName" value="Gurram" /> 
  <property name="id" value="553" /> 
 </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> 

</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.

<bean id="commonEmployee" class="com.springtutorial.model.Employee">

         <property name="address" ref="address" />

</bean>

        

Above snippet creates commonEmployee bean.

<bean id="employee1" class="com.springtutorial.model.Employee" parent="commonEmployee">

         <property name="firstName" value="Hari Krishna" />

         <property name="lastName" value="Gurram" />

         <property name="id" value="553" />

</bean>

“employee1” inherit address property from commonEmployee bean using “parent” attribute.

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 24, 2015 11:13:24 PM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh 
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1873a6: startup date [Tue Mar 24 23:13:24 IST 2015]; root of context hierarchy 
Mar 24, 2015 11:13:24 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions 
INFO: Loading XML bean definitions from class path resource [spring.xml] 
Employee [firstName=Hari Krishna, lastName=Gurram, id=553, address=Address [street=Chowdeswari temple, city=Bangalore, state=Karnataka, country=India, pin=560037]] 
Mar 24, 2015 11:13:25 PM org.springframework.context.support.ClassPathXmlApplicationContext doClose 
INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@1873a6: startup date [Tue Mar 24 23:13:24 IST 2015]; root of context hierarchy 

Final project structure looks like below.

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