The first form is preferable to the second, because using the idref tag lets thecontainer validate at deployment time that the referenced, named bean actuallyexists. In the second variation, no validation is performed on the value that is passedto the targetName property of the client bean. Typos are only discovered (with mostlikely fatal results) when the client bean is actually instantiated. If the clientbean is a prototype bean, this typo and the resulting exceptionmay only be discovered long after the container is deployed.
In most application scenarios, most beans in the container aresingletons. When a singleton bean needs tocollaborate with another singleton bean or a non-singleton bean needs to collaboratewith another non-singleton bean, you typically handle the dependency by defining onebean as a property of the other. A problem arises when the bean lifecycles aredifferent. Suppose singleton bean A needs to use non-singleton (prototype) bean B,perhaps on each method invocation on A. The container creates the singleton bean A onlyonce, and thus only gets one opportunity to set the properties. The container cannotprovide bean A with a new instance of bean B every time one is needed.
Prototype 2 Password.txt.rar
Lookup method injection is the ability of the container to override methods oncontainer-managed beans and return the lookup result for another named bean in thecontainer. The lookup typically involves a prototype bean, as in the scenario describedin the preceding section. The Spring Frameworkimplements this method injection by using bytecode generation from the CGLIB library todynamically generate a subclass that overrides the method.
The bean identified as commandManager calls its own createCommand() methodwhenever it needs a new instance of the myCommand bean. You must be careful to deploythe myCommand bean as a prototype if that is actually what is needed. If it isa singleton, the same instance of the myCommandbean is returned each time.
The non-singleton prototype scope of bean deployment results in the creation of a newbean instance every time a request for that specific bean is made. That is, the beanis injected into another bean or you request it through a getBean() method call on thecontainer. As a rule, you should use the prototype scope for all stateful beans and thesingleton scope for stateless beans.
In contrast to the other scopes, Spring does not manage the complete lifecycle of aprototype bean. The container instantiates, configures, and otherwise assembles aprototype object and hands it to the client, with no further record of that prototypeinstance. Thus, although initialization lifecycle callback methods are called on allobjects regardless of scope, in the case of prototypes, configured destructionlifecycle callbacks are not called. The client code must clean up prototype-scopedobjects and release expensive resources that the prototype beans hold. To getthe Spring container to release resources held by prototype-scoped beans, try using acustom bean post-processor, which holds a reference tobeans that need to be cleaned up.
When you use singleton-scoped beans with dependencies on prototype beans, be aware thatdependencies are resolved at instantiation time. Thus, if you dependency-inject aprototype-scoped bean into a singleton-scoped bean, a new prototype bean is instantiatedand then dependency-injected into the singleton bean. The prototype instance is the soleinstance that is ever supplied to the singleton-scoped bean.
However, suppose you want the singleton-scoped bean to acquire a new instance of theprototype-scoped bean repeatedly at runtime. You cannot dependency-inject aprototype-scoped bean into your singleton bean, because that injection occurs onlyonce, when the Spring container instantiates the singleton bean and resolvesand injects its dependencies. If you need a new instance of a prototype bean atruntime more than once, see Method Injection.
To support the scoping of beans at the request, session, application, andwebsocket levels (web-scoped beans), some minor initial configuration isrequired before you define your beans. (This initial setup is not requiredfor the standard scopes: singleton and prototype.)
The bean scoping mechanism is extensible. You can define your ownscopes or even redefine existing scopes, although the latter is considered bad practiceand you cannot override the built-in singleton and prototype scopes.
The first argument to the registerScope(..) method is the unique name associated witha scope. Examples of such names in the Spring container itself are singleton andprototype. The second argument to the registerScope(..) method is an actual instanceof the custom Scope implementation that you wish to register and use.
As of Spring Framework 4.3, you may also declare a factory method parameter of typeInjectionPoint (or its more specific subclass: DependencyDescriptor) toaccess the requesting injection point that triggers the creation of the current bean.Note that this applies only to the actual creation of bean instances, not to theinjection of existing instances. As a consequence, this feature makes most sense forbeans of prototype scope. For other scopes, the factory method only ever sees theinjection point that triggered the creation of a new bean instance in the given scope(for example, the dependency that triggered the creation of a lazy singleton bean).You can use the provided injection point metadata with semantic care in such scenarios.The following example shows how to use InjectionPoint:
As noted earlier, lookup method injection is anadvanced feature that you should use rarely. It is useful in cases where asingleton-scoped bean has a dependency on a prototype-scoped bean. Using Java for thistype of configuration provides a natural means for implementing this pattern. Thefollowing example shows how to use lookup method injection:
By using Java configuration, you can create a subclass of CommandManager wherethe abstract createCommand() method is overridden in such a way that it looks up a new(prototype) command object. The following example shows how to do so: 2ff7e9595c
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