JAVA EE: @Bean

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Monday, 29 October 2018

Spring bean java based configuration using @Configuration and @Bean[employee and address]

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Java-Based Configuration in Spring

Java-based configuration allows developers to define and wire Spring beans entirely using pure Java classes instead of lengthy XML configuration files. This modern approach provides full compile-time type safety, effortless refactoring, and clean code navigation inside your IDE.

In this guide, you will learn how to configure inter-bean dependencies—specifically wiring an Address bean into an Employee bean—using the @Configuration and @Bean annotations.

Understanding @Configuration and @Bean

@Configuration: Annotates the class to indicate that it contains bean definition methods for the Spring IoC container.
@Bean: Placed over a method to declare that its return value should be registered as a bean within the Spring application context.
Inter-Bean Dependencies: When one bean requires another (e.g., an Employee needing an Address), you can directly invoke the corresponding @Bean method to wire the dependency seamlessly.

Core Implementation Steps

Define POJOs: Create simple Address and Employee domain models with standard getters, setters, or constructors.
Create Configuration Class: Annotate a class with @Configuration and declare @Bean methods that instantiate and populate both objects.
Bootstrap with AnnotationConfigApplicationContext: Initialize the context using new AnnotationConfigApplicationContext(AppConfig.class) to retrieve and use your managed beans.

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Spring bean java based configuration using @Configuration and @Bean[employee and address]

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;

import org.springframework.beans.factory.annotation.Autowired;

public class Employee

{

    private int id;

    private String name;

    @Autowired

    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

                + "]";

    }

}

ApplicationBeans.java

package com.ram.config;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import com.ram.model.Address;

import com.ram.model.Employee;

/**

 * Annotate with @Configuration to tell Spring that this is the core

 * Spring configuration file, and define bean via @Bean.

 */

@Configuration

public class ApplicationBeans

{

    @Bean(name = "address")

    public Address getAddress()

    {

        Address address = new Address();

        address.setCity("TamilNadu");

        address.setState("Chennai");

        return address;

    }

    @Bean(name = "employee")

    public Employee getEmployee()

    {

        Employee employee = new Employee();

        employee.setId(100);

        employee.setName("Peter");

        return employee;

    }

}

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.ram.config.ApplicationBeans;

import com.ram.model.Employee;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new AnnotationConfigApplicationContext(

                ApplicationBeans.class);

        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

Oct 02, 2018 9:40:30 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@5f4da5c3: startup date [Tue Oct 02 09:40:30 IST 2018]; root of context hierarchy

---------------------------------------

Got employee object from the ApplicationContext(Spring Container)

Employee [id=100, name=Peter, address=Address [city=TamilNadu, state=Chennai]]