Spring学习（四）——自动装配Bean

r囧r小猫 2022-12-31 11:24 250阅读 0赞

### 自动装配Bean ###

*  三种装配Bean
 *  环境搭建
 *  java中显式装配
 *   *  @Configuration
 *  隐式的自动装配bean
 *   *  byName自动装配
     *  byType自动装配
 *  @Resource和@ Autowired的区别

自动装配Bean是Spring满足bean依赖的一种方式  
Spring会在上下文中自动寻找，并自动给bean装配属性

# 三种装配Bean #

*  1、在xml中显式装配 在之前的配置都是用xml显式装配
 *  2、在java中显式装配
 *  3、隐式的自动装配bean

# 环境搭建 #

**实体类**

package com.my.pojo;
    
    public class Cat {
        
        public void shout(){
        
            System.out.println("miaomiao");
        }
    }
    
    public class Dog {
        
        public void shout(){
        
            System.out.println("wangwang");
        }
    }
    
    
    package com.my.pojo;
    
    public class People {
        
    
        private String name;
        private Cat cat;
        private Dog dog;
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public Cat getCat() {
        
            return cat;
        }
    
        public void setCat(Cat cat) {
        
            this.cat = cat;
        }
    
        public Dog getDog() {
        
            return dog;
        }
    
        public void setDog(Dog dog) {
        
            this.dog = dog;
        }
    
        @Override
        public String toString() {
        
            return "People{" +
                    "name='" + name + '\'' +
                    ", cat=" + cat +
                    ", dog=" + dog +
                    '}';
        }
    }

**配置**

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd">
    
    
        <bean id="cat" class="com.my.pojo.Cat"/>
        <bean id="dog" class="com.my.pojo.Dog"/>
    
        <bean id="people" class="com.my.pojo.People">
            <property name="name" value="奥特曼"/>
            <property name="dog" ref="dog"/>
            <property name="cat" ref="cat"/>
        </bean>
    
    </beans>

**测试运行**

import com.my.pojo.People;
    import org.junit.jupiter.api.Test;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class MyTest {
        
        @Test
        public void test(){
        
            ApplicationContext context =  new ClassPathXmlApplicationContext("beans.xml");
            People people = context.getBean("people", People.class);
            people.getDog().shout();
            people.getCat().shout();
        }
    }
    
    wangwang
    miaomiao

# java中显式装配 #

完全不使用Spring配置，全权交给java实现  
JavaConfig是Spring的一个子项目：在Spring4之后成为一个核心功能  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70]

package com.my.pojo;
    
    
    import org.springframework.beans.factory.annotation.Value;
    import org.springframework.stereotype.Component;
    
    
    // 等价于在配置文件中的<bean id="user" class="com.my.pojo.User"/>
    @Component
    public class User {
        
        @Value("lalalala")
        public String name ;
    
    }
    
    
    package com.my.config;
    
    
    import com.my.pojo.User;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    
    @Configuration
    public class MyConfig {
        
    
        @Bean
        public User getUser(){
        
            return new User();
        }
    
    }
    
    
    import com.my.config.MyConfig;
    import com.my.pojo.User;
    import org.junit.Test;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    
    public class MyTest {
        
        @Test
        public void Test(){
        
            ApplicationContext context =  new AnnotationConfigApplicationContext(MyConfig.class);
            User user = (User) context.getBean("getUser");
            System.out.println(user.getName());
    
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70 2]

## @Configuration ##

这个也会被Spring容器托管，注册到容器中，因为他本来就是一个@Component，@Configuration代表这是一个配置类和之前的beans.xml是一样的  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70 4]

# 隐式的自动装配bean #

## byName自动装配 ##

**会自动在容器上下文中查找和自己对象set方法后面的值对应的beanId且beanId唯一**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70 5]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70 6]

## byType自动装配 ##

**会自动在容器上下文中查找和自己对象属性类型相同的bean但是要保证类型全局唯一**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoYXJfbQ_size_16_color_FFFFFF_t_70 7]

# @Resource和@ Autowired的区别 #

*  ·都是用来自动装配的。都可以放在属性字段上
 *  · Autowired通过byType的方式实现，而且必须要求这个对象存在!【常用】
 *  .Resource默认通过byname的方式实现，如果找不到名字，则通过byType实现!如果两个都找不到的情况下，就报错!【常用】
 *  ·执行顺序不同:@Autowired 通过byType的方式实现。@Resource默认通过byname的方式实现。

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