bean的自动装配

在Spring中由三种装配方式：

• xml中显式的配置

• java中显式的配置

• 隐式的自动装配bean

1.环境搭建

Dog.java:

package com.kakafa.pojo;

public class Dog {
    public void shout(){
        System.out.println("bark!");
    }
}

Cat.java:

package com.kakafa.pojo;

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

People.java:

package com.kakafa.pojo;

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

    public String getName() {
        return name;
    }

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

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

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.kakafa.pojo.Cat"/>
    <bean id="dog" class="com.kakafa.pojo.Dog"/>
    
    <bean id="people" class="com.kakafa.pojo.People">
        <property name="name" value="邓孝慈"/>
        <property name="cat" ref="cat"/>
        <property name="dog" ref="dog"/>
    </bean>


</beans>

test:

import com.kakafa.pojo.People;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

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



    }
}

2.自动装配

原来:

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

    <bean id="people" class="com.kakafa.pojo.People">
        <property name="name" value="邓孝慈"/>
        <property name="cat" ref="cat"/>
        <property name="dog" ref="dog"/>
    </bean>

自动装配：

1.byName

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

    <bean id="people" class="com.kakafa.pojo.People" autowire="byName">
        <property name="name" value="邓孝慈"/>
    </bean>

• byName只能取到小写，大写取不到;
• 不区分大小写的说法不准确，set/get方法生成会自动将属性首字母大写,所以Spring也只是会自动把set和get后面的第一个字符变为小写。

2.byType

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

    <bean id="people" class="com.kakafa.pojo.People" autowire="byType">
        <property name="name" value="邓孝慈"/>
    </bean>