M05 Q03 What is a web application context? What extra scopes does it offer?

Web Application Context is a Spring Application Context for Web Applications that runs under Embedded or Standalone Application Server that supports Servlet API and acts as Servlet Container.

Web Application Context is described by WebApplicationContext interface and it allows you to access ServletContext interface from Servlet API.

Web Application Context provides four additional scopes:

• Request Scope
• Session Scope
• Application Scope
• Websocket Scope

Request Scope

• Defined by @RequestScope annotation
• Bean lifecycle is tightly coupled with HTTP Request lifecycle
• New Bean instance is created for each request

Session Scope

• Defined by @SessionScope annotation
• Bean lifecycle is tightly coupled with HTTP Session lifecycle
• New Bean is created for each new session and Bean instance lives as long as HTTP Session is alive

Application Scope

• Defined by @ApplicationScope annotation
• Bean lifecycle is tightly coupled with ServletContext
• One Bean instance available per entire Web Application – ServletContext
• Differences compared to Singleton Bean:
• Singleton per ServletContext, not per Spring Application Context (one Web Application may have several Spring Application Contexts)
• Exposed via attribute of ServletContext

Websocket Scope

• Defined by @Scope annotation with specified properties:

@Scope(scopeName = "websocket", proxyMode = ScopedProxyMode.TARGET_CLASS) 

• Bean lifecycle is coupled with lifecycle of WebSocket Session, however bean usually lives longer then WebSocket Session