How to inject the inner bean in spring using Setter dependency Injection

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Introduction

In the Spring Framework, dependencies are often wired using standalone bean definitions referenced via the ref attribute. However, when a collaborating bean is dedicated entirely to a specific parent bean and should not be accessed anywhere else in your application, defining it as an Inner Bean inside a <property> tag is the ideal design pattern.

Why Use Inner Beans with Setter Injection?

• Complete Encapsulation: Inner beans do not require an id or name attribute. The container completely hides them from external lookup via context.getBean().
• Cleaner XML Configuration: Keeps your configuration tidy by nesting tightly-coupled helper beans directly where they are used.
• Flexibility: Setter-based injection allows flexible dependency wiring and optional configurations after object construction.

Step-by-Step Configuration Example

Consider an Employee bean that has an address property populated using a setter method (setAddress(Address address)).

1. Declaring the Inner Bean in XML

<bean id="employee" class="com.ram.model.Employee">
    <property name="id" value="101" />
    <property name="name" value="John" />
    <property name="address">
        <!-- Inner Bean Definition via Setter -->
        <bean class="com.ram.model.Address">
            <property name="city" value="San Francisco" />
            <property name="state" value="CA" />
            <property name="country" value="USA" />
        </bean>
    </property>
</bean>

2. Loading the Application Context

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

Employee emp = (Employee) context.getBean("employee");
emp.displayDetails();

Key Takeaway

Inner beans injected via setter methods are anonymous and tied directly to the lifecycle of their enclosing bean. They are never exposed to other beans in the IoC container, ensuring strong encapsulation and clean component boundaries.

Recommended Related Tutorials from Ram N Java

• How to Inject dependent Object using Spring dependency injection by Setter method?
• Spring Dependency Injection via Setter Method: Injecting Primitive Values and Strings
• How to Inject Map using Spring dependency injection by Setter method? | Spring Tutorial

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How to inject the inner bean in spring using Setter dependency Injection

How to inject the inner bean in spring using Setter dependency Injection

How to inject the inner bean in spring using Setter dependency Injection

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%20http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.ram.core</groupId>
    <artifactId>SpringDemo</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>SpringDemo</name>
    <url>http://maven.apache.org</url>

    <properties>
        <spring.version>5.0.2.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

        <!-- Spring 5 dependencies -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>

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

Address.java

package com.ram.model;

public class Address
{
    private String city;
    private String state;

    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;
    }

    @Override
    public String toString()
    {
        return "Address [city=" + city + ", state=" + state + "]";
    }

}

Employee.java

package com.ram.model;

public class Employee
{
    private int id;
    private String name;
    private Address address;

    public int getId()
    {
        return id;
    }

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

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public Address getAddress()
    {
        return address;
    }

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

    @Override
    public String toString()
    {
        return "Employee [id=" + id + ", name=" + name + ", address=" + address
                + "]";
    }

}

applicationContext.xml

<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-4.3.xsd">

    <bean id="employee" class="com.ram.model.Employee">
        <property name="id" value="100"></property>
        <property name="name" value="Peter"></property>

        <property name="address">

            <bean class="com.ram.model.Address">
                <property name="city" value="TamilNadu"></property>
                <property name="state" value="Chennai"></property>
            </bean>

        </property>
    </bean>

</beans>

App.java

package com.ram.core;

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

import com.ram.model.Employee;

public class App
{
    public static void main(String[] args)
    {
        ApplicationContext context = new ClassPathXmlApplicationContext(
                "applicationContext.xml");

        System.out.println("---------------------------------------");

        Employee employee = (Employee) context.getBean("employee");
        System.out.println(
                "Got employee object from the ApplicationContext(Spring Container)");

        System.out.println(employee);

    }

}

Output

Jul 14, 2018 8:24:14 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sat Jul 14 08:24:14 IST 2018]; root of context hierarchy
Jul 14, 2018 8:24:15 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
---------------------------------------
Got employee object from the ApplicationContext(Spring Container)
Employee [id=100, name=Peter, address=Address [city=TamilNadu, state=Chennai]]

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