七、对象依赖注入

　依赖注入是指运行时将容器内对象利用反射赋给其他对象的操作，依赖注入有两种形式  1.基于setter方法注入对象  2.基于构造方法注入对象。

基于setter方法注入对象包含两种使用场景 

　1.利用setter实现静态数值注入(value)

<?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="sweetApple" class="com.spring.ioc.entity.Apple">
        
        <property name="title" value="红富士">property>
        <property name="color" value="红色">property>
        <property name="origin" value="欧洲">property>
　　　　　
    bean>
beans>

package com.spring.ioc;

import com.spring.ioc.entity.Apple;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringApplication {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
        Apple sweetApple = context.getBean("sweetApple", Apple.class);
        System.out.println(sweetApple.getTitle());
    }
}
//Apple的setTitle方法

/*public void setTitle(String title) {
    System.out.println("title属性设置为："+title);
    this.title = title;
}*/

springIoC会将value中字符串自动转换成目标属性的类型，比如Intege

　2.利用setter方法实现对象注入(ref)

<?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="sweetApple" class="com.spring.ioc.entity.Apple">
        
        <property name="title" value="红富士">property>
        <property name="color" value="红色">property>
        <property name="origin" value="欧洲">property>
        <property name="price" value="19.8">property>
    bean>

    <bean id="lily" class="com.spring.ioc.entity.Child">
        <property name="name" value="莉莉">property>
        
        <property name="apple" ref="sweetApple">property>
    bean>
beans>

package com.spring.ioc;

import com.spring.ioc.entity.Apple;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringApplication {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
        Apple sweetApple = context.getBean("sweetApple", Apple.class);
        //System.out.println(sweetApple.getTitle());
    }
}

基于构造方法注入对象

<?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="sourApple" class="com.spring.ioc.entity.Apple">
        <property name="title" value="青苹果">property>
        <property name="color" value="绿色">property>
        <property name="origin" value="中亚">property>
        <property name="price" value="9.8">property>
    bean>

    <bean id="andy" class="com.spring.ioc.entity.Child">
        <constructor-arg name="name" value="安迪">constructor-arg>
        <constructor-arg name="apple" ref="sourApple">constructor-arg>
    bean>
beans>

package com.spring.ioc;

import com.spring.ioc.entity.Apple;
import com.spring.ioc.entity.Child;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringApplication {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
        Child andy = context.getBean("andy", Child.class);
        andy.eat();
    }
}