Spring快速入门-05-Bean的自动装配

7. Bean的自动装配

7.1. 环境搭建及测试

1. 环境搭建

1. 编写实体类Cat, Dog, People

package com.kuang.pojo;

public class Cat {
    public void shout() {
        System.out.println("miao~");
    }
}

package com.kuang.pojo;

public class Dog {
    public void shout() {
        System.out.println("wang~");
    }
}

package com.kuang.pojo;

public class People {
    private Cat cat;
    private Dog dog;
    private String 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;
    }

    public String getName() {
        return name;
    }

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

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

1. 编写spring配置文件beans.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="cat" class="com.kuang.pojo.Cat"/>
    <bean id="dog" class="com.kuang.pojo.Dog"/>

    <bean id="people" class="com.kuang.pojo.People">
        <property name="name" value="哇哈哈"/>
        <property name="cat" ref="cat"/>
        <property name="dog" ref="dog"/>

    </bean>

</beans>

1. 测试

import com.kuang.pojo.People;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        People people = context.getBean("people", People.class);
        people.getCat().shout();
        people.getDog().shout();
    }
}

7.2. ByName自动装配

package com.kuang.pojo;

public class People {
    private Cat cat;
    private Dog dog;
    private String 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;
    }

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Perple{" +
        "cat=" + cat +
        ", dog=" + dog +
        ", name='" + 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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="cat" class="com.kuang.pojo.Cat"/>
    <bean id="dog" class="com.kuang.pojo.Dog"/>

    <bean id="people" class="com.kuang.pojo.People" autowire="byName">
        <property name="name" value="哇哈哈"/>
    </bean>

</beans>

byName:会自动在容器上下文中查找，和自己对象set方法后而的值对应的beanid！

7.3. ByType自动装配

<?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.kuang.pojo.Cat"/>
  <bean id="dog" class="com.kuang.pojo.Dog"/>

  <bean id="people" class="com.kuang.pojo.People" autowire="byType">
    <property name="name" value="哇哈哈"/>
  </bean>

</beans>

byType:会自动在容器上下文中查找，和自己对象属性类型机同的bean！

小结：

• byname的时候，需要保证所有bean的id唯一，并且这个bean需要和自动注入的属性的set方法的值一致！
• bytype的时候，需要保证所有bean的class唯一，并且这个bean需要和自动注入的属性的类型一致！

7.4. 使用注解实现自动装配

1. 修改beans.xml

• 导入context约束
• 配置注解的支持：<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"
       xmlns:aop="http://www.springframework.org/schema/aop"
       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
        http://www.springframework.org/schema/aop
        https://www.springframework.org/schema/context/spring-aop.xsd">

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

    <bean id="cat" class="com.kuang.pojo.Cat"/>
    <bean id="dog" class="com.kuang.pojo.Dog"/>
    <bean id="people" class="com.kuang.pojo.People"/>


</beans>

1. 修改People.java

 @Autowired
    private Cat cat;
    @Autowired
    private Dog dog;

• 直接在属性上使用！也可以在set方式上使用！
• 使用Autowired我们可以不用编写Set方法了，前提是你这个自动装配的属性在IOC（Spring)容器中存在，且符合名字byname！

1. 测试

import com.kuang.pojo.People;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        People people = context.getBean("people", People.class);
        people.getCat().shout();
        people.getDog().shout();
    }
}

小结，@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！
• @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。