使用注解实现Spring自动装配

概述

实现Spring自动装配的注解有两个：@Autowired和@Resource，两个注解的区别如下：

1. @Autowired

   • 出处：这是Spring的注解
   • 用法：可以放在属性上面（这时候可以省略setter方法），也可以放在setter方法上面，一般放在属性上面即可
   • 实现方式：通过byType的方式实现，需要保证所有bean的class唯一，即不可以存在相同类型的bean
   • 指定要装配的bean的id的方式：可以使用@Qualifier注解指定bean的id，这个注解使用value属性指定bean的id

2. @Resource

   • 出处：这是JDK的注解
   • 用法：放在属性上面
   • 实现方式：默认通过byName的方式实现，如果找不到名字，则通过byType实现，需要保证所有bean的class唯一，即不可以存在相同类型的bean；如果两个都找不到的情况下，就报错
   • 指定要装配的bean的id的方式：指定bean的id的方式有3种：①根据Setter方法名指定自动装配的bean的id，例如：Setter的方法名为setDog1，所以bean的id就必须为dog1②通过@Resource注解的name属性指定bean的id③可以使用@Qualifier注解指定bean的id，这个注解使用value属性指定bean的id。特别地，②和③一起用，②的方式有效

代码实现

@Autowired

ApplicationContext.xml

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

    <!--开启注解的支持-->
    <context:annotation-config/>

    <bean id="dog1" class="com.ledao.entity.Dog">
        <property name="name" value="小哈1"/>
    </bean>
    <bean id="dog2" class="com.ledao.entity.Dog">
        <property name="name" value="小哈2"/>
    </bean>
    <bean id="cat1" class="com.ledao.entity.Cat">
        <property name="name" value="小花1"/>
    </bean>

    <bean id="people" class="com.ledao.entity.People">
        <property name="name" value="tom"/>
    </bean>
</beans>

Dog实体类

package com.ledao.entity;

/**
 * @author LeDao
 * @company
 * @create 2022-02-15 18:14
 */
public class Dog {

    private String name;

    public Dog() {
        System.out.println("狗吃骨头");
    }

    public String getName() {
        return name;
    }

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

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

Cat实体类

package com.ledao.entity;

/**
 * @author LeDao
 * @company
 * @create 2022-02-15 18:14
 */
public class Cat {

    private String name;

    public Cat() {
        System.out.println("猫吃鱼");
    }

    public String getName() {
        return name;
    }

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

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

People实体类

package com.ledao.entity;

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

/**
 * @author LeDao
 * @company
 * @create 2022-02-15 18:13
 */
public class People {

    private String name;
    @Autowired
    @Qualifier(value = "dog2")
    private Dog dog;
    @Autowired
    private Cat cat;

    public String getName() {
        return name;
    }

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

    public Dog getDog() {
        return dog;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    public Cat getCat() {
        return cat;
    }

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    @Override
    public String toString() {
        return "People{" +
                "name='" + name + '\'' +
                ", dog=" + dog +
                ", cat=" + cat +
                '}';
    }
}

测试

import com.ledao.entity.People;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author LeDao
 * @company
 * @create 2022-02-12 15:56
 */
public class MyTest {

    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("ApplicationContext.xml");
        People people = context.getBean("people", People.class);
        System.out.println(people);
    }
}

结果

@Resource

对比

和@Autowired的代码对比，只改动了People实体类

People实体类

package com.ledao.entity;

import javax.annotation.Resource;

/**
 * @author LeDao
 * @company
 * @create 2022-02-15 18:13
 */
public class People {

    private String name;
    @Resource(name = "dog2")
    private Dog dog;
    @Resource
    private Cat cat;

    public String getName() {
        return name;
    }

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

    public Dog getDog() {
        return dog;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    public Cat getCat() {
        return cat;
    }

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    @Override
    public String toString() {
        return "People{" +
                "name='" + name + '\'' +
                ", dog=" + dog +
                ", cat=" + cat +
                '}';
    }
}