bean的作用域

bean的作用域

理论知识

bean的作用域有6种类型，官网的描述在这里

Scope	Description
singleton	(Default) Scopes a single bean definition to a single object instance for each Spring IoC container.
prototype	Scopes a single bean definition to any number of object instances.
request	Scopes a single bean definition to the lifecycle of a single HTTP request. That is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
session	Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
application	Scopes a single bean definition to the lifecycle of a ServletContext. Only valid in the context of a web-aware Spring ApplicationContext.
websocket	Scopes a single bean definition to the lifecycle of a WebSocket. Only valid in the context of a web-aware Spring ApplicationContext.

核心的两种作用域是singleton和prototype
singleton 即单例，指所有获取的该实例均为同一个实例
prototype 即原型，指每次获取该实例都会新创建一个
其他4种作用域只能在web开发中使用到

实践

User实体类

package com.kuangstudy.di;

/**
 * 功能描述
 *
 * @since 2022-06-25
 */
public class User {
    private String name;
    private String age;

    public String getName() {
        return name;
    }

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

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public User() {
    }

    public User(String name, String age) {
        this.name = name;
        this.age = age;
    }

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

配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:p="http://www.springframework.org/schema/p"
    xmlns:c="http://www.springframework.org/schema/c" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
  https://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="u1" class="com.kuangstudy.di.User" p:age="20" p:name="xiaoming" scope="singleton"></bean>
    <bean id="u2" class="com.kuangstudy.di.User" c:age="30" c:name="xiaohong" scope="prototype"></bean>

</beans>

测试类

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.kuangstudy.di.Student;
import com.kuangstudy.di.User;

/**
 * 功能描述
 *
 * @since 2022-06-25
 */
public class Test01 {
    @Test
    public void test2() {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans1.xml");
        User u1_1 = context.getBean("u1", User.class);
        User u1_2 = context.getBean("u1", User.class);
        System.out.println(u1_1 == u1_2);
        User u2_1 = context.getBean("u2", User.class);
        User u2_2 = context.getBean("u2", User.class);
        System.out.println(u2_1 == u2_2);
    }
}

结果

true
false