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There is a public Bean ,A Users and B Shared by users , If A In use , Public resources Bean Revised , It can lead to B The user made an error while using .

A user （Controller9） When using, it is modified ：

@Controller
public class UserController9 {
    @Autowired
    private User user1;

    public User getUser() {
        User user = user1;
        user.setName(" Tang's monk ");
        return user;
    }
}

B user （Controller9） Use public resources ：

@Controller
public class UserController10 {
    @Autowired
    private User user1;

    public User getUser() {
        return user1;
    }
}

public class User {
    private int id;
    private String name;
    private String password;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

public class App {
    public static void main(String[] args) {
        // 1.  obtain spring Context 
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");

        UserController9 userController9 = context.getBean(UserController9.class);
        System.out.println("Controller9 : " + userController9.getUser());

        UserController10 userController10 = context.getBean(UserController10.class);
        System.out.println("Controller10 : " + userController10.getUser());
    }
}

 Output ：Controller9 : User{id=1, name=' Tang's monk ', password='123'}
      Controller10 : User{id=1, name=' Tang's monk ', password='123'}

In fact, we want Controller10 Output ：Controller10 : User{id=1, name=' Zhang San ', password='123'}

public class App {
    public static void main(String[] args) {
        // 1.  obtain spring Context 
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");

        if(userController9 == userController9_2) {
            System.out.println(" Memory addresses are equal , The singleton pattern ");
            System.out.println(userController9);
            System.out.println(userController9_2);
        } else {
            System.out.println(" Memory addresses are not equal , Not singleton mode ");
            System.out.println(userController9);
            System.out.println(userController9_2);
        }
    }
}

 Output ：
 Memory addresses are equal , The singleton pattern 
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[email protected]

Using singleton mode will greatly improve performance , therefore spring in Bean The default scope of is The singleton pattern （singleton）. That is, all people use the same object .

2. Scope definition

After the occurrence of the above problems , Limits the available range of variables in the program , That is to define Scope .
Bean Scope of action Refer to Bean stay Spring Some kind of behavior pattern in the whole framework , For example, singleton scope , It means Bean Throughout Spring Only one of them , And it is shared globally , After others modify this value , What people behind read is the modified value .

2.1 Bean Of 6 Species scope

Spring The container is initializing a Bean When an instance of the , The scope of the instance is also specified .

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

The first two are Spring Core scope , The last four are Spring MVC Scope in

2.1.1 singleton Single case scope

describe ： Under this scope Bean stay loC In the container There is only one instance ： obtain Bean（applicationContext.getBean Other methods ） And assembly Bean （ adopt @Autowired notes ⼊） It's all the same thing .

scene ： No state Of Bean Use this scope , Stateless means Bean The attribute state of the object No need to update

Spring The scope is selected by default

2.1.2 prototype Prototype scope （ Multiple scope ）

describe ： Every time you make a comparison of Bean All requests will Create a new instance ： obtain Bean And assembly Bean Are instances of experience objects .

scene ： A stateful Of Bean Use this scope

2.1.3 request Request scope

describe ： Every time http Request meeting Create a new Bean example , Be similar to prototype
scene ： once http Get requests and responses share Bean
stay SpringMVC Use in

2.1.4 session Conversation scope

   describe ： In a http session Define a Bean example
   scene ： Of the user session share Bean , such as ： Record a user's login information
   stay SpringMVC Use in

2.1.5 application Global scope （ Understanding can ）

2.1.6 websocket（ Understanding can ）

Single case scope （singleton） and Global scope （application） The difference between ：

The scope of the single case is Spring Core （ Common projects ） Scope of action , The global scope is Spring Web Scope in .
The scope of a singleton acts on loC The container of , and The global scope works on Servlet Containers .

2.2 Set scope

@Scope Tags can modify both methods and classes ,@Scope There are two settings ：

1. Set the value directly ：@Scope（"prototype"）
2. （ Constant ） Similar to enumeration settings ：@Scope（ConfigurableBeanFactory.SCOPE_PROTOTYPE）

@Component
public class UserBeans2 {

    @Bean(name = "user1")
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    public User user1(){
        User user = new User();
        user.setId(1);
        user.setName(" Zhang San ");
        user.setPassword("123");
        return user;
    }
}

@Controller
public class UserController9 {
    @Autowired
    private User user1;

    public User getUser() {
        User user = user1;
        user.setName(" Tang's monk ");
        return user;
    }
}

public class App {
    public static void main(String[] args) {
        // 1.  obtain spring Context 
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
        UserController9 userController9 = context.getBean(UserController9.class);
        System.out.println("Controller9 : " + userController9.getUser());

        UserController10 userController10 = context.getBean(UserController10.class);
        System.out.println("Controller10 : " + userController10.getUser());

        }
    }
}

 Output ：Controller9 : User{id=1, name=' Tang's monk ', password='123'}
        Controller10 : User{id=1, name=' Zhang San ', password='123'}

modify UserBeans2 Code ：

@Component
public class UserBeans2 {

    @Bean(name = "user1")
    @Scope(ConfigurableBeanFactory.SCOPE_SINGLETON)
    public User user1(){
        User user = new User();
        user.setId(1);
        user.setName(" Zhang San ");
        user.setPassword("123");
        return user;
    }
}

Output ：

Controller9 : User{id=1, name=' Tang's monk ', password='123'}
Controller10 : User{id=1, name=' Tang's monk ', password='123'}

3. Bean Principle analysis

3.1 Spring Execute the process

start-up Spring Containers -----》 Complete according to the configuration Bean initialization -----》Bean Object registered to Spring Containers in （ save ）-----》 take Bean Assemble into the required class （ take ）