Singleton and Prototype Bean Scopes

1. Introduction

In Spring, bean scope defines how many objects of a bean are created and managed by the IoC container.

Main scopes:

Singleton
Prototype

2. Singleton Scope

Singleton is the default scope in Spring.

Key Features

Only one instance is created
Same object is shared across the application
Created at container startup (by default)
Best for stateless beans

3. Example of Singleton Scope

Step 1: Add Dependency

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<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.3.30</version>
</dependency>

Step 2: Create Bean Class

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package bean;

public class HelloWorld {

    private String name;

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

    public String getName() {
        return name;
    }
}

Step 3: Configure XML

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<bean id="hw"
      class="bean.HelloWorld"
      scope="singleton"/>

Step 4: Client Code

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package driver;

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

public class Client {

    public static void main(String[] args) {

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

        HelloWorld obj1 = (HelloWorld) context.getBean("hw");
        obj1.setName("Anil");

        HelloWorld obj2 = (HelloWorld) context.getBean("hw");

        System.out.println(obj1.getName());
        System.out.println(obj2.getName());

        System.out.println(obj1 == obj2);
    }
}

Output Understanding

Both objects are same
Changes in one object reflect in another

4. Prototype Scope

Prototype scope creates a new object every time the bean is requested.

Key Features

Multiple instances are created
New object for every getBean() call
Container manages creation only
Best for stateful beans

5. Example of Prototype Scope

XML Configuration

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<bean id="prototypeBean"
      class="bean.HelloWorld"
      scope="prototype"/>

Client Code

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HelloWorld obj1 = (HelloWorld) context.getBean("prototypeBean");
obj1.setName("First");

HelloWorld obj2 = (HelloWorld) context.getBean("prototypeBean");

System.out.println(obj1.getName());
System.out.println(obj2.getName());

System.out.println(obj1 == obj2);

Output Understanding

Objects are different
Changes are not shared

6. Singleton vs Prototype

Instance Creation

Singleton: One object per container
Prototype: New object every time

Object Sharing

Singleton: Shared
Prototype: Not shared

Default Scope

Singleton: Yes
Prototype: No

Usage

Singleton: Stateless beans
Prototype: Stateful beans

7. Conclusion

Singleton is used in most applications
Prototype is used when you need multiple objects
Choose scope based on application requirement