Bean scope in Spring

Table of Contents

1. What is the scope of Bean?

2. @Scope annotation

3. Six scopes of Bean

3.1 singleton singleton mode

3.2 prototype prototype mode

3.3 request

3.4 sessions

3.5 application

3.6 websockets

1. What is the scope of Bean

In the previous learning process, we defined scope as:Limiting the available range of variables in the program, or defining a certain area of variables. However, in Bean, this scope refers to a certain behavior of the Bean in the Spring framework. Next, let’s analyze a case

First create a User class, and at the same time create a Users class to store the User object in Spring. Here, annotations are used, and this method will be adopted in the future.

public class User {
    private String name;
    private int id;
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + ''' +
                ", id=" + id +
                '}';
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
}

@Component
public class Users {
    @Bean
    public User user() {
        User user = new User();
        user.setName("Public Name");
        user.setId(1);
        return user;
    }
}

There is a requirement here that a developer needs to obtain the object of this User class and change the original “public name” in the User class object to Zhang San, and the original class name cannot be modified!

In this operation, the developer did not directly use the user object to modify its attributes, but created another user1 to receive the user and modify the name attribute in user1.

@Controller
public class UserController1 {
    @Resource
    private User user;
    public void setName() {
        User user1 = user;
        user1.setName("Zhang San");
        System.out.println(user1);
    }
}

Configure the annotation scan path in the Spring configuration file, and then obtain the class object through the factory provided by Spring. Through testing we found that it was successful.

@Test
public void test() {
    ApplicationContext ctx = new ClassPathXmlApplicationContext("spring-config.xml");
    UserController1 userController1 = ctx.getBean("userController1", UserController1.class);
    userController1.setName();
} 

According to the idea, the original user class should not be modified here, but suddenly one day another developer needs to obtain the contents of the original user class.

@Controller
public class UserController2 {
    @Resource
    private User user;
    public void getUser() {
        System.out.println(user);
    }
}

public void test() {
    ApplicationContext ctx = new ClassPathXmlApplicationContext("spring-config.xml");
    //Here is the first developer's
    UserController1 userController1 = ctx.getBean("userController1", UserController1.class);
    userController1.setName();
    // second developer's
    UserController2 userController2 = ctx.getBean("userController2", UserController2.class);
    userController2.getUser();
}

When testing here, you will find that there is a problem. The name in the original class has also been modified. In fact, this is what we call the scope of the Bean. Because the default scope of the Bean is Singleton >, so only one object will be created here!

@Component
public class Users {
    @Bean("user")
    @Scope("prototype")
    public User user() {
        User user = new User();
        user.setName("Public Name");
        user.setId(1);
        return user;
    }
}

@Component
public class Users {
    @Bean("user")
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    public User user() {
        User user = new User();
        user.setName("Public Name");
        user.setId(1);
        return user;
    }
}