Spring 自动装配bean注解

什么是bean自动装配？

1. 自动装配是Spring满足bean依赖的一种方式
2. Sping会在配置文件上下文中自动寻找，并给bean转配属性

装配方式（Autowired）

1. XML中显示配置
2. 在java中显示配置
3. 隐式的自动装配

autowire属性

属性对应值如下

byName：会自动在容器中查找和而自己对象set方法后面的值对应的beanid(如果使用自动创建的set方法，set后面的第一个会默认变小写)

byType：会自动在容器中查找和而自己对象属性相同的beanid;！！要保证类型全局唯一==bean的class唯一！！

<bean name="people" class="com.liu.pojo.Person" autowire="byType">
          <property name="name" value="lili"/>
 </bean>

注解@Autowired（使用此属性可以忽略set方法）

1. 首先要使用该注解必须更新配置文件
   添加的语句是：
   xmlns:context=“http://www.springframework.org/schema/context” http://www.springframework.org/schema/context
   https://www.springframework.org/schema/context/spring-context.xsd
   context:annotation-config/

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:context="http://www.springframework.org/schema/context"
   xsi:schemaLocation="http://www.springframework.org/schema/beans
       https://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       https://www.springframework.org/schema/context/spring-context.xsd">
   <context:annotation-config/>
</beans>

测试类：

import com.liu.pojo.Person;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringTest {
    
    
    @Test
    public void usuallyTest(){
    
    
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        Person people = context.getBean("people", Person.class);
        System.out.println(people);
    }
}

结果如图：

2. 自动装配，一般放在属性字段上

法1：单独使用@Autowirted

@Autowired默认按照byType装配对象

xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
   <context:annotation-config/>
   <bean name="animal" class="com.liu.pojo.Animal"/>
   <bean name="cat" class="com.liu.pojo.Cat"/>
   <bean name="dog" class="com.liu.pojo.Dog"/>
   <bean id="people" class="com.liu.pojo.Person">
      <property name="name" value="lili" />
   </bean>
</beans>

  	package com.liu.pojo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.lang.Nullable;

public class Person {
    
    
    @Autowired
    private Cat cat;
    @Autowired
    private Dog dog;
    private String name;
    public Cat getCat() {
    
    
        return cat;
    }
    public void setCat(@Nullable Cat cat) {
    
    
        this.cat = cat;
    }

    public Dog getDog() {
    
    
        return dog;
    }
    public void setDog(@Nullable Dog dog) {
    
    
        this.dog = dog;
    }
    public String getName() {
    
    
        return name;
    }
    public void setName(String name) {
    
    
        this.name = name;
    }
    @Override
    public String toString() {
    
    
        return name + "拥有" + cat.getName() +
                dog.getName();
    }
}

法2：@Autowired配合@Qualifier(value = “XXX”)使用,指定对象《==》byName

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
   <context:annotation-config/>
   <bean name="animal" class="com.liu.pojo.Animal"/>
   <bean id="cat1" class="com.liu.pojo.Cat"/>
   <bean id="dog1" class="com.liu.pojo.Dog"/>
   <bean id="people" class="com.liu.pojo.Person">
      <property name="name" value="lili" />
   </bean>
</beans>

  @Autowired
    @Qualifier(value = "cat1")
    private Cat cat;
    @Autowired
    @Qualifier(value = "dog1")
    private Dog dog;
    private String name;

扩展：法3( @Resource 或者@Resource(name = “dog”))使用与@Autowirted类似

注意： @Resource 通过的是属性name

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
   <context:annotation-config/>
   <bean name="animal" class="com.liu.pojo.Animal"/>
   <bean name="cat" class="com.liu.pojo.Cat"/>
   <bean name="dog" class="com.liu.pojo.Dog"/>
   <bean id="people" class="com.liu.pojo.Person">
      <property name="name" value="lili" />
   </bean>
</beans>

    @Resource(name = "cat")
    private Cat cat;
    @Resource(name = "dog")
    private Dog dog;
    private String name;

注解（ @Resource，@Autowired）小结：

• 两者都可自动装配，都可以写在属性上
• @Autowired默认通过bytpe方式实现，而且必须要求这个对象存在
• @Resource默认通过byname方式实现，如果找不到名字则通过bytype实现。如果两种方式都找不到，就报错

@component注解

使用准备

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
   <!--包扫描,在这个包下的注解都会生效-->
   <context:component-scan base-package="com.liu.pojo"/>
   <context:annotation-config/>
</beans>

使用

@Component（作用在类上）相当于 <bean name="" class=""/>
@value（作用在属性上）相当于  <property name="" value=""/>

package com.liu.pojo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class Student {
    
    
    @Value("李四")
    private String sName;
    @Value("19")
    private String sId;

    public String getsName() {
    
    
        return sName;
    }

    public void setsName(String sName) {
    
    
        this.sName = sName;
    }

    public String getsId() {
    
    
        return sId;
    }

    public void setsId(String sId) {
    
    
        this.sId = sId;
    }

    @Override
    public String toString() {
    
    
        return "Student{" +
                "sName='" + sName + '\'' +
                ", sId='" + sId + '\'' +
                '}';
    }
}

XML与注解小结

• xml更万能，适用于任何场景，维护简单
• 注解不是自己的类是用不了，维护相对复杂
• 若要让注解生效，必须开启注解支持

使用java方式配置Spring

使用到的注解：@Configuration @Bean

1. 创建一个java文件（BeanConfig.java）用于配置

@Configuration  （作用在类上）相当于<beans/>
@Bean（作用在方法上）相当于  <bean name="" class=""/>
@import(.class) 导入其他配置文件

import com.liu.pojo.Teacher;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class BeanConfig {
    
    

    @Bean
    public Teacher getTeacher() {
    
    
        return new Teacher();
    }
}

2. 使用 @Bean注册对象
   Teacher .java

package com.liu.pojo;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
public class Teacher {
    
    
    @Value("张三")
    private String tName;
    @Value("0001")
    private String tId;

    public String gettName() {
    
    
        return tName;
    }

    public void settName(String tName) {
    
    
        this.tName = tName;
    }

    public String gettId() {
    
    
        return tId;
    }

    public void settId(String tId) {
    
    
        this.tId = tId;
    }

    @Override
    public String toString() {
    
    
        return "Teacher{" +
                "tName='" + tName + '\'' +
                ", tId='" + tId + '\'' +
                '}';
    }
}

3. 使用@Component注册对象，beanid默认类名第一个字母小写
   Teacher .java

package com.liu.pojo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class Teacher {
    
    
    @Value("张三")
    private String tName;
    @Value("0001")
    private String tId;

    public String gettName() {
    
    
        return tName;
    }

    public void settName(String tName) {
    
    
        this.tName = tName;
    }

    public String gettId() {
    
    
        return tId;
    }

    public void settId(String tId) {
    
    
        this.tId = tId;
    }

    @Override
    public String toString() {
    
    
        return "Teacher{" +
                "tName='" + tName + '\'' +
                ", tId='" + tId + '\'' +
                '}';
    }
}

3. 测试：

import com.liu.appConfig.BeanConfig;
import com.liu.pojo.Teacher;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class SpringTest {
    
    
    @Test
    public void ComponentTest(){
    
    
        ApplicationContext context = new AnnotationConfigApplicationContext(BeanConfig.class);
        //通过@Bean注册
        //Teacher getTeacher = context.getBean("getTeacher", Teacher.class);
        //通过@ComponentScan()包注册，让类中的注解生效@Component
        Teacher user = context.getBean("teacher", Teacher.class);
        System.out.println(user);
    }
}