Scope and lifecycle of beans

One 、 What is? Bean Scope of action

Bean The scope of can be understood as Bean stay Spring Something in the whole framework Patterns of behavior , It can also be understood as Bean The type of .

Two 、Bean Of 5 Species scope

1. singleton: Single case scope
2. prototype： Prototype scope （ Multiple scope ）
3. request： Request scope
4. session： Conversation scope
5. application： Global scope

request session application These three scopes are based on web Of Spring WebApplicationContext Realized , Only in web It can only be used in the environment .

2.1 Singleton

If Bean The scope of is declared as Singleton, So in Spring Only one shared... Will be created in the container bean example . For all bean request , as long as id With this bean The definition matches , that Spring The same... Will be returned every time you need it bean example .
Singleton It's a singleton model , When you create a container, you create a bean object ,Singleton yes Spring Default scope in , Sure scope=(" ")" To set the scope .
Use scenarios ： Usually No state Of Bean Use this scope . Stateless means Bean The property state of the object does not need to be updated .

2.2 prototype

When a scope is prototype when , It means a Bean The definition corresponds to multiple object instances . Declare as prototype The scope of will result in every time the bean A new... Is created when requested bean example .
prototype Is a prototype type ,** It was not instantiated when we created the container , But when we get bean Only when you create an object .** The object obtained each time is not the same object .

Use scenarios ： It is usually stateful Bean Use this scope .

2.3 Request

When HTTP The scope of the request call is request Of bean when , Every time you add one HTTP request ,Spring I'm going to create a new one bean, Destroy this in time after the request is processed bean.

2.4 session

session All requests in share the same request bean example .Session Destroy when finished bean.

2.5 application

Servlet The container is the whole Web Application development uses appPreferences bean Define once to create AppPreferences bean example .

application And singleton There are some differences ：

• It's every ServletContext Single case , Not every one of them Spring Application Single case .
• It's public , Therefore, it can be seen as a ServletContext attribute .

3、 ... and 、Bean Life cycle of

Life cycle refers to the whole life cycle of an object from birth to destruction .
String Bean The life cycle of can be divided into the following five parts ：

1. Instantiation
2. Attribute assignment
3. initialization
4. Use
5. The destruction

• Instantiation ： First step , Instantiate a bean object .
• Attribute assignment ： The second step , by bean Set related properties and dependencies
• initialization ：3,4 Step is executed before initialization ,5,6 The first step is to really initialize , The first 7 Step is executed after initialization , After initialization , You can start using it bean 了
• The destruction ：9,10 Step real destruction bean

We use a specific chestnut to explain this process ：

PersonBean My life ：