Package org.springframework.beans.factory.config

# Interface Scope

public interface Scope
Strategy interface used by a `ConfigurableBeanFactory`, representing a target scope to hold bean instances in. This allows for extending the BeanFactory's standard scopes `"singleton"` and `"prototype"` with custom further scopes, registered for a `specific key`.

`org.springframework.context.ApplicationContext` implementations such as a `org.springframework.web.context.WebApplicationContext` may register additional standard scopes specific to their environment, for example, `"request"` and `"session"`, based on this Scope SPI.

Even if its primary use is for extended scopes in a web environment, this SPI is completely generic: It provides the ability to get and put objects from any underlying storage mechanism, such as an HTTP session or a custom conversation mechanism. The name passed into this class's `get` and `remove` methods will identify the target object in the current scope.

`Scope` implementations are expected to be thread-safe. One `Scope` instance can be used with multiple bean factories at the same time, if desired (unless it explicitly wants to be aware of the containing BeanFactory), with any number of threads accessing the `Scope` concurrently from any number of factories.

Since:
  2.0
Author:
  Juergen Hoeller, Rob Harrop
See Also:
  - `ConfigurableBeanFactory.registerScope(java.lang.String, org.springframework.beans.factory.config.Scope)`
  - `CustomScopeConfigurer`
  - `org.springframework.aop.scope.ScopedProxyFactoryBean`
  - `org.springframework.web.context.request.RequestScope`
  - `org.springframework.web.context.request.SessionScope`

## Method Summary

Modifier and Type
Method
Description
`Object`
`get(String name, ObjectFactory<?> objectFactory)`
Return the object with the given name from the underlying scope, `creating it` if not found in the underlying storage mechanism.
`String`
`getConversationId()`
Return the conversation ID for the current underlying scope, if any.
`void`
`registerDestructionCallback(String name, Runnable callback)`
Register a callback to be executed on destruction of the specified object in the scope (or at destruction of the entire scope, if the scope does not destroy individual objects but rather only terminates in its entirety).
`Object`
`remove(String name)`
Remove the object with the given `name` from the underlying scope.
`Object`
`resolveContextualObject(String key)`
Resolve the contextual object for the given key, if any.

## Method Details

### get

Object get(String name, ObjectFactory<?> objectFactory)
Return the object with the given name from the underlying scope, `creating it` if not found in the underlying storage mechanism.

This is the central operation of a Scope, and the only operation that is absolutely required.

Parameters:
  `name` - the name of the object to retrieve
  `objectFactory` - the `ObjectFactory` to use to create the scoped object if it is not present in the underlying storage mechanism
Returns:
  the desired object (never `null`)
Throws:
  `IllegalStateException` - if the underlying scope is not currently active

### remove

@Nullable Object remove(String name)
Remove the object with the given `name` from the underlying scope.

Returns `null` if no object was found; otherwise returns the removed `Object`.

Note that an implementation should also remove a registered destruction callback for the specified object, if any. It does, however, not need to execute a registered destruction callback in this case, since the object will be destroyed by the caller (if appropriate).

Note: This is an optional operation. Implementations may throw `UnsupportedOperationException` if they do not support explicitly removing an object.

Parameters:
  `name` - the name of the object to remove
Returns:
  the removed object, or `null` if no object was present
Throws:
  `IllegalStateException` - if the underlying scope is not currently active
See Also:
  - `registerDestructionCallback(java.lang.String, java.lang.Runnable)`

### registerDestructionCallback

void registerDestructionCallback(String name, Runnable callback)
Register a callback to be executed on destruction of the specified object in the scope (or at destruction of the entire scope, if the scope does not destroy individual objects but rather only terminates in its entirety).

Note: This is an optional operation. This method will only be called for scoped beans with actual destruction configuration (DisposableBean, destroy-method, DestructionAwareBeanPostProcessor). Implementations should do their best to execute a given callback at the appropriate time. If such a callback is not supported by the underlying runtime environment at all, the callback must be ignored and a corresponding warning should be logged.

Note that 'destruction' refers to automatic destruction of the object as part of the scope's own lifecycle, not to the individual scoped object having been explicitly removed by the application. If a scoped object gets removed via this facade's `remove(String)` method, any registered destruction callback should be removed as well, assuming that the removed object will be reused or manually destroyed.

Parameters:
  `name` - the name of the object to execute the destruction callback for
  `callback` - the destruction callback to be executed. Note that the passed-in Runnable will never throw an exception, so it can safely be executed without an enclosing try-catch block. Furthermore, the Runnable will usually be serializable, provided that its target object is serializable as well.
Throws:
  `IllegalStateException` - if the underlying scope is not currently active
See Also:
  - `DisposableBean`
  - `AbstractBeanDefinition.getDestroyMethodName()`
  - `DestructionAwareBeanPostProcessor`

### resolveContextualObject

@Nullable Object resolveContextualObject(String key)
Resolve the contextual object for the given key, if any. For example, the HttpServletRequest object for key "request".

Parameters:
  `key` - the contextual key
Returns:
  the corresponding object, or `null` if none found
Throws:
  `IllegalStateException` - if the underlying scope is not currently active

### getConversationId

@Nullable String getConversationId()
Return the conversation ID for the current underlying scope, if any.

The exact meaning of the conversation ID depends on the underlying storage mechanism. In the case of session-scoped objects, the conversation ID would typically be equal to (or derived from) the `session ID`; in the case of a custom conversation that sits within the overall session, the specific ID for the current conversation would be appropriate.

Note: This is an optional operation. It is perfectly valid to return `null` in an implementation of this method if the underlying storage mechanism has no obvious candidate for such an ID.

Returns:
  the conversation ID, or `null` if there is no conversation ID for the current scope
Throws:
  `IllegalStateException` - if the underlying scope is not currently active