Singleton Bean Scope in Spring

Singleton Bean Scope: Scopes a single bean definition to a single object instance per Spring IoC container. This is the default behavior of the spring container
When a bean is a singleton, only one shared instance of the bean will be managed, and all requests for beans with an id or ids matching that bean definition will result in that one specific bean instance being returned by the Spring container.
We can say another way, when you define a bean definition and it is scoped as a singleton, then the Spring IoC container will create exactly one instance of the object defined by that bean definition. This single instance will be stored in a cache of such singleton beans, and all 

Lets see with example which show the singleton scope of the ‘zeroPoint’ bean in the spring container.


Point.java

package com.dineshonjava.sdnext.beanscope.tutorial;

public class Point
{
 private int x;
 private int y;
 /**
  * @return the x
  */
 public int getX() {
  return x;
 }
 /**
  * @param x the x to set
  */
 public void setX(int x) {
  this.x = x;
 }
 /**
  * @return the y
  */
 public int getY() {
  return y;
 }
 /**
  * @param y the y to set
  */
 public void setY(int y) {
  this.y = y;
 }
}


spring.xml

<beans xmlns:aop="http://www.springframework.org/schema/aop" xmlns:p="http://www.springframework.org/schema/p" xmlns:>
DrawingApp.java
package com.dineshonjava.sdnext.beanscope.tutorial;

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

/**
 * @author Dinesh Rajput
 *
 */
public class DrawingApp 
{
 /**
  * @param args
  */
 public static void main(String[] args) 
 {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");

Point point1 = (Point) context.getBean("zeroPoint");
Point point2 = (Point) context.getBean("zeroPoint");
if(point1 == point2)
 System.out.println("In Singleton Demo >> Both are same objects values are.." +
     "n 1. point1= "+point1+" n 2. point2= "+point2);
else
  System.out.println("In Protptype Demo >> Both are different objects values are.." +
     "n 1. point1= "+point1+" n 2. point2= "+point2);
 }
}
Output:
Jun 28, 2012 9:10:46 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@ab50cd: startup date [Thu Jun 28 21:10:46 IST 2012]; root of context hierarchy
Jun 28, 2012 9:10:46 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring.xml]
Jun 28, 2012 9:10:46 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1543c88: defining beans [zeroPoint]; root of factory hierarchy

In Singleton Demo >> Both are same objects values are..
1. point1= com.dineshonjava.sdnext.beanscope.tutorial.Point@1198891
2. point2= com.dineshonjava.sdnext.beanscope.tutorial.Point@1198891

Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the above message: See the both address value of the object is same.
Bean scopes using annotation:


spring.xml

<beans xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p" xmlns:>

Here component-scan element has attribute 'base-package'. base-package contain the base package of the Bean class.

base-package = "com.dineshonjava.sdnext.beanscope.tutorial"

Ponit.java
package com.dineshonjava.sdnext.beanscope.tutorial;

import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Service;

@Service
@Scope("singleton")
public class Point
{
 private int x;
 private int y;
 /**
  * @return the x
  */
 public int getX() {
  return x;
 }
 /**
  * @param x the x to set
  */
 public void setX(int x) {
  this.x = x;
 }
 /**
  * @return the y
  */
 public int getY() {
  return y;
 }
 /**
  * @param y the y to set
  */
 public void setY(int y) {
  this.y = y;
 }
}

Annotation @Service:
Target : Class
Description:
Here @Service is streotype annotation which declared above the class name that means this class is a bean of the spring container.
In Spring container this bean recognized by the id "point" means that same as the class name except first letter of the class name is the small letter.
for example: class 'Point' get as 'point' bean
                    class 'Circle' get as 'circle' bean
Annotation @Scope:
Target : Class
Description:
Here @Scope is annotation which declared above the class name that define the scope the bean

 @Scope("singleton")
 @Scope("prototype")

DrawingApp.java

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

import com.dineshonjava.sdnext.beanscope.tutorial.Point;
/**
 * @author Dinesh Rajput
 *
 */
public class DrawingApp 
{
 /**
  * @param args
  */
 public static void main(String[] args) 
 {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Point point1 = (Point) context.getBean("point");
Point point2 = (Point) context.getBean("point");
if(point1 == point2)
  System.out.println("In Singleton Demo >> Both are same objects values are.." +
  "n 1. point1= "+point1+" n 2. point2= "+point2);
else
  System.out.println("In Protptype Demo >> Both are different objects values are.." +
  "n 1. point1= "+point1+" n 2. point2= "+point2);
 }
}
Output:
Jun 28, 2012 10:22:04 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@145d068: startup date [Thu Jun 28 22:22:04 IST 2012]; root of context hierarchy
Jun 28, 2012 10:22:04 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring.xml]
Jun 28, 2012 10:22:04 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1cbfe9d: defining beans [point,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy

In Singleton Demo >> Both are same objects values are..
1. point1= com.dineshonjava.sdnext.beanscope.tutorial.Point@84da23
2. point2= com.dineshonjava.sdnext.beanscope.tutorial.Point@84da23

Spring Related Topics you may like
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  3. Spring MVC Interview Questions
  4. Spring Security Interview Questions and Answers
  5. Spring REST Interview Questions and Answers
  6. Spring Boot Interview Questions and Answers
  7. Spring Boot Microservices Interview Questions and Answers
  8. Dependency Injection (DI) in Spring
  9. Spring IoC Container
  10. What is Bean Factory in Spring
  11. ApplicationContext in Spring
  12. Bean Autowiring in Spring
  13. Spring Bean Scopes
  14. Create Custom Bean Scope in Spring Example
  15. Using ApplicationContextAware in Spring
  16. Spring Bean Life Cycle and Callbacks
  17. BeanPostProcessor in Spring
  18. BeanFactoryPostProcessor in Spring
  19. Annotations in Spring and Based Configuration
  20. Spring JSR-250 Annotations
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  23. Method injection with Spring using Lookup method property
  24. Spring AOP-Introduction to Aspect Oriented Programming
  25. @Aspect Annotation in Spring
  26. Spring AOP AspectJ @Before Annotation Advice Example
  27. Spring AOP Before Advice Example using XML Config
  28. Spring AOP AspectJ @After Annotation Advice Example
  29. Spring AOP After Advice Example using XML Config
  30. Spring AOP AspectJ @AfterReturning Annotation Advice Example
  31. Spring AOP After-Returning Advice Example using XML Config
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  33. Spring AOP After Throwing Advice Example using XML Config
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  35. Spring AOP Around Advice Example using XML Config
  36. Spring AOP Proxies in Spring
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  41. Spring Security Java Based Configuration with Example
  42. Spring Security XML Namespace Configuration Example
                              Bean Scope in The Spring
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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!

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