Spring Useful Resources

Spring - Injecting Inner Beans

Quiz

As you know Java inner classes are defined within the scope of other classes, similarly, inner beans are beans that are defined within the scope of another bean. Thus, a <bean/> element inside the <property/> or <constructor-arg/> elements is called inner bean and it is shown below.

<?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 = "outerBean" class = "...">
      <property name = "target">
         <bean id = "innerBean" class = "..."/>
      </property>
   </bean>

</beans>

Example - Injecting Inner Beans

Let us have working Eclipse IDE in place and follow the following steps to create a Spring application −

Steps	Description
1	Create a Maven project with a name spring, groupid com.tutorialspoint, artifactid spring and create a package com.tutorialspoint under the src folder in the created project.
2	Update the pom.xml as explained in the Spring - Environment Setup chapter.
3	Create Java classes TextEditor, SpellChecker and MainApp under the com.tutorialspoint package.
4	Create Beans configuration file Beans.xml under the src/main/resources folder.
5	The final step is to create the content of all the Java files and Bean Configuration file. Finally, run the application as explained below.

TextEditor.java

package com.tutorialspoint;

public class TextEditor {
   private SpellChecker spellChecker;
   
   // a setter method to inject the dependency.
   public void setSpellChecker(SpellChecker spellChecker) {
      System.out.println("Inside setSpellChecker." );
      this.spellChecker = spellChecker;
   }
   
   // a getter method to return spellChecker
   public SpellChecker getSpellChecker() {
      return spellChecker;
   }
   public void spellCheck() {
      spellChecker.checkSpelling();
   }
}

SpellChecker.java

package com.tutorialspoint;

public class SpellChecker {
   public SpellChecker(){
      System.out.println("Inside SpellChecker constructor." );
   }
   public void checkSpelling(){
      System.out.println("Inside checkSpelling." );
   }
}

MainApp.java

package com.tutorialspoint;

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

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
      TextEditor te = (TextEditor) context.getBean("textEditor");
      te.spellCheck();
   }
}

Beans.xml

Following is the configuration file Beans.xml which has configuration for the setter-based injection but using inner beans −

<?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">

   <!-- Definition for textEditor bean using inner bean -->
   <bean id = "textEditor" class = "com.tutorialspoint.TextEditor">
      <property name = "spellChecker">
         <bean id = "spellChecker" class = "com.tutorialspoint.SpellChecker"/>
      </property>
   </bean>

</beans>

Output

Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it will print the following message −

Inside SpellChecker constructor.
Inside setSpellChecker.
Inside checkSpelling.

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