In-Depth Analysis of Bean Scopes in Aspectran

Aspectran’s IoC container supports the concept of Scope, which specifies the range for managing the lifecycle of a Bean. The scope determines when a bean instance is created, how long it is maintained, and how it is destroyed. It provides four standard scopes defined in the com.aspectran.core.context.rule.type.ScopeType enum class.

1. SINGLETON

• Definition: Only one instance is created within the ActivityContext for a single bean definition. It is created when the container is initialized, and all subsequent requests for that bean will share this unique instance.
• Lifecycle: It is maintained from the start to the end of the ActivityContext.
• Internal Behavior: BeanRegistry stores the instance of a singleton bean in an internal cache (usually a Map). When a bean request comes in, it first looks for the bean with the corresponding ID in the cache. If it exists, it is returned immediately. If it does not exist, a new one is created, registered in the cache, and then returned.
• Primary Use Case: Suitable for components that should be shared regardless of the thread, such as stateless service objects, DAOs, and configuration classes.
• Caution: Since it is accessed by multiple threads simultaneously, if it has a mutable state, thread-safety must be ensured through synchronization.
• Configuration Alias: singleton

2. PROTOTYPE

• Definition: A new instance is created each time a bean is requested. Unlike a singleton, no instance is shared at all.
• Lifecycle: The container is only involved in the creation and dependency injection of a prototype bean. Once the bean is created and delivered to the client code, it is out of the container’s management. That is, the destruction of the created instance is handled by the garbage collector (GC), and destruction-related callback methods like @Destroy are not called.
• Internal Behavior: When BeanRegistry receives a request for a prototype-scoped bean, it creates a new object via the new keyword based on the information defined in the BeanRule, injects dependencies, and returns it. There is no caching process.
• Primary Use Case: Suitable for stateful objects. It is used when an independent state needs to be maintained for each request.
• Caution: Since a new object is created each time, it can cause more overhead than a singleton.
• Configuration Alias: prototype

3. REQUEST

• Definition: Creates a single instance that is valid only for the lifecycle of a single request. The same instance is always returned within the same request, but a new instance is created for a different request.
• Lifecycle: It is created when a request starts and destroyed when that request ends.
• Internal Behavior: This scope is only valid in an environment that supports RequestAdapter. When an Activity starts, it stores the scoped bean in the internal storage of the RequestAdapter (usually a Map). If the bean is requested again within the same request, it is retrieved from this storage and returned. When the request processing is finished and the Activity is destroyed, the destruction callbacks of all request-scoped beans stored in the RequestAdapter are called.
• Environmental Constraint: It is only meaningful in a web environment where a RequestAdapter exists, such as WebActivity or TowActivity. Attempting to use this scope in an environment like ShellActivity or DaemonActivity will result in an UnsupportedBeanScopeException.
• Primary Use Case: Suitable for objects that handle data related to an HTTP request (e.g., request parameters, user authentication information).
• Configuration Alias: request

4. SESSION

• Definition: Creates a single instance that is valid within a single user session. The same instance is always returned within the same session, but a new instance is created for a different session.
• Lifecycle: It is created when a session first starts and destroyed when that session is invalidated.
• Internal Behavior: This scope is only valid in an environment that supports SessionAdapter. SessionAdapter internally wraps HttpSession or Aspectran’s own SessionManager, and session-scoped beans are stored as attributes of this session. When the session is destroyed, the destruction callbacks of all session-scoped beans stored in the session are called.
• Environmental Constraint: It is only meaningful in an environment where a SessionAdapter exists, such as when the session feature is enabled in WebActivity or ShellService. Using it in an environment without session functionality will result in an UnsupportedBeanScopeException.
• Primary Use Case: Suitable for objects that manage data that needs to be maintained per user (e.g., login information, shopping cart).
• Configuration Alias: session

5. Summary