Spring Bean Definition Inheritance
March 12, 2023
parent property of <bean> element. We need to assign parent bean id to parent property in child bean. We can also create XML template which will be inherited by child bean. To create template bean, we have to create a bean using abstract property of bean element without assigning a class. We need to assign abstract property value as true. We cannot directly use this bean in application. We can only inherit its property in our child bean. This type of bean is a pure template bean. In case of annotation, Java inheritance is enough.
Here on this page, we will provide complete example of Spring bean definition inheritance.
Contents
Spring Bean Definition Inheritance with XML Configuration using Parent Property
In XML configuration, we inherit bean definition using beanparent property. The classes configured in XML must be in super class and sub-class relation so that child bean should be compatible with parent bean. All the properties defined are overridden by child bean. We can override the properties of parent bean and can add new properties in the child bean.
app-conf-1.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.xsd">
<bean id="animal" class="com.concretepage.Animal" init-method="initA">
<property name="name" value="Hathi"/>
<property name="age" value="20"/>
</bean>
<bean id="elephant" class="com.concretepage.Elephant" parent="animal" init-method="initE">
<property name="age" value="30"/>
<property name="location" value="Varanasi"/>
</bean>
</beans>
animal and another bean with the name elephant. The elephant bean is using parent property to inherit the bean properties of animal. We are also overriding parent bean properties and adding new property to child bean. Find the java classes.
Animal.java
package com.concretepage;
public class Animal {
private String name;
private Integer age;
public void initA() {
System.out.println("Inside initA()");
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
package com.concretepage;
public class Elephant extends Animal {
private String location;
public void initE() {
System.out.println("Inside initE()");
}
public String getLocation() {
return location;
}
public void setLocation(String location) {
this.location = location;
}
}
ClassPathXmlApplicationContext we are running our XML configuration demo.
SpringDemo.java
package com.concretepage;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class SpringDemo {
public static void main(String[] args) {
AbstractApplicationContext context = new ClassPathXmlApplicationContext("app-conf-1.xml");
Elephant elephant=(Elephant)context.getBean("elephant");
System.out.println(elephant.getLocation());
System.out.println(elephant.getName());
System.out.println(elephant.getAge());
context.registerShutdownHook();
}
}
animal bean has been inherited in child bean elephant. Find the output.
Inside initA() Inside initE() Varanasi Hathi 30
Template Bean Definition with Abstract Property in XML Configuration
In XML configuration, we can also create a template bean. Template bean is created as abstract bean usingabstract property of bean tag. Template bean cannot be accessed directly. It can only be inherited. In child bean we can override template bean properties and can also add new properties. In template bean, class property is not required. We need to use abstract property as abstract="true"
app-conf-2.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.xsd">
<bean id="template" abstract="true">
<property name="name" value="Hathi"/>
<property name="age" value="30"/>
</bean>
<bean id="animal" class="com.concretepage.Animal" parent="template">
<property name="age" value="50"/>
</bean>
<bean id="elephant" class="com.concretepage.Elephant" parent="animal">
<property name="location" value="Delhi"/>
</bean>
</beans>
SpringDemo class changing the line as below
AbstractApplicationContext context = new ClassPathXmlApplicationContext("app-conf-2.xml");
Delhi Hathi 50
Spring Bean Definition Inheritance Example using Annotation
In case of spring bean definition inheritance using annotation, java inheritance is enough. There is no way to create abstract bean in java configuration. To achieve same functionality of XML based bean definition into java configuration, we can do as follows.Find the java configuration file.
AppConfig.java
package com.concretepage;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class AppConfig {
@Bean
public Elephant elephant() {
Elephant elephant = new Elephant();
initAnimal(elephant);
elephant.setLocation("Delhi");
return elephant;
}
private void initAnimal(Animal animal) {
animal.setName("Hathi");
animal.setAge(30);
}
}
SpringDemo.java
package com.concretepage;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class SpringDemo {
public static void main(String[] args) {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.register(AppConfig.class);
ctx.refresh();
Elephant elephant = ctx.getBean(Elephant.class);
System.out.println(elephant.getName());
System.out.println(elephant.getLocation());
System.out.println(elephant.getAge());
ctx.registerShutdownHook();
}
}
Hathi Delhi 30
