Spring Bean Scopes allows us to have more granular control of the bean instances creation. Sometimes we want to create bean instance as singleton but in some other cases we might want it to be created on every request or once in a session.
Spring Bean Scopes
There are five types of spring bean scopes:
- singleton - only one instance of the spring bean will be created for the spring container. This is the default spring bean scope. While using this scope, make sure bean doesn’t have shared instance variables otherwise it might lead to data inconsistency issues.
- prototype – A new instance will be created every time the bean is requested from the spring container.
- request – This is same as prototype scope, however it’s meant to be used for web applications. A new instance of the bean will be created for each HTTP request.
- session – A new bean will be created for each HTTP session by the container.
- global-session – This is used to create global session beans for Portlet applications.
Spring Bean Singleton and Prototype Scope
Spring bean singleton and prototype scopes can be used in standalone spring apps. Let’s see how we can easily configure these scopes using @Scope annotation. Let’s say we have a java bean class.
package com.journaldev.spring; public class MyBean { public MyBean() { System.out.println("MyBean instance created"); } }Let’s define the spring configuration class where we will define the method to get MyBean instance from spring container.
package com.journaldev.spring; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Scope; @Configuration public class MyConfiguration { @Bean @Scope(value="singleton") public MyBean myBean() { return new MyBean(); } }Note that singleton is default scope, so we can remove @Scope(value="singleton") from above bean definition. Now let’s create a main method and test the singleton scope.
When above program is executed, we will get output like below.
MyBean instance created 867988177 867988177Notice that both MyBean instances have same hashcode and the constructor is called once once, it means that spring container is returning the same instance of MyBean always. Now let’s change the scope to prototype.
@Bean @Scope(value="prototype") public MyBean myBean() { return new MyBean(); }This time we will get following output when main method is executed.
MyBean instance created 867988177 MyBean instance created 443934570It’s clear that MyBean instance is created every time it’s requested from spring container. Now let’s change the scope to request.
@Bean @Scope(value="request") public MyBean myBean() { return new MyBean(); }In this case, we will get following exception.
It’s because request, session and global-session scopes are not available for standalone applications.
Spring Bean Request and Session Scope
For spring bean request and session scope example, we will create Spring Boot web application. Create a spring boot starter project and choose “web” so that we can run it as a web application.
Let’s create some spring components and configure them as spring beans in the spring container with scope as request and session.
Spring Bean Request Scope
package com.journaldev.spring; import org.springframework.context.annotation.Scope; import org.springframework.context.annotation.ScopedProxyMode; import org.springframework.stereotype.Component; @Component @Scope(value = "request", proxyMode = ScopedProxyMode.TARGET_CLASS) public class DataRequestScope { private String name = "Request Scope"; public DataRequestScope() { System.out.println("DataRequestScope Constructor Called"); } public String getName() { return name; } public void setName(String name) { this.name = name; } }Spring Bean Session Scope
package com.journaldev.spring; import org.springframework.context.annotation.Scope; import java.time.LocalDateTime; import org.springframework.context.annotation.ScopedProxyMode; import org.springframework.stereotype.Component; @Component @Scope(value = "session", proxyMode = ScopedProxyMode.TARGET_CLASS) public class DataSessionScope { private String name = "Session Scope"; public DataSessionScope() { System.out.println("DataSessionScope Constructor Called at "+LocalDateTime.now()); } public String getName() { return name; } public void setName(String name) { this.name = name; } }Spring Component
Now let’s create a spring component and use spring to auto configure above beans.
package com.journaldev.spring; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; @Component public class Customer { @Autowired private DataRequestScope dataRequestScope; @Autowired private DataSessionScope dataSessionScope; public DataRequestScope getDataRequestScope() { return dataRequestScope; } public void setDataRequestScope(DataRequestScope dataRequestScope) { this.dataRequestScope = dataRequestScope; } public DataSessionScope getDataSessionScope() { return dataSessionScope; } public void setDataSessionScope(DataSessionScope dataSessionScope) { this.dataSessionScope = dataSessionScope; } }Spring Rest Controller
Finally, let’s create a RestController class and configure some API end points for our testing purposes.
Spring Boot Session Timeout Configuration
Finally we have to configure spring boot session timeout variables, add below properties in src/main/resources/application.properties.
server.session.cookie.max-age= 1 server.session.timeout= 1Now our spring beans with session scope will be invalidated in one minute. Just run the SpringBootMvcApplication class as spring boot application. You should see below output for our endpoints being configured.
2018-05-23 17:02:25.830 INFO 6921 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/nameRS]}" onto public java.lang.String com.journaldev.spring.HelloData.helloRS() 2018-05-23 17:02:25.831 INFO 6921 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/nameSSUpdated]}" onto public java.lang.String com.journaldev.spring.HelloData.helloSSUpdated() 2018-05-23 17:02:25.832 INFO 6921 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/nameSS]}" onto public java.lang.String com.journaldev.spring.HelloData.helloSS()Spring Bean Request Scope Test
Open any browser and go to URL //localhost:8080/nameRS and check the console output. You should see DataRequestScope Constructor Called getting printed on each request.
Spring Bean Session Scope Test
Go to //localhost:8080/nameSS and you would get following output.
You can download the Spring Beans Scope Spring Boot project from our GitHub Repository.