八、装配bean--自动装配

一、有时候，我们不想一个一个地去配置一个个ref，希望spring智能一点，让那些对象类型属性自动找到配置文件中同名的，或者类型匹配的bean填充进去。

public class Employee {
    private String name;
}

public class Department {
    private String name;
    private Employee employee;
}

<bean id="department" class="com.beans.Department" autowire="byName">
        <property name="name" value="财务部"/>
    </bean>
    
    <bean id="employee" class="com.beans.Employee">
        <property name="name" value="蔡文姬"/>
    </bean>

autowire="byName"的意思是根据名字自动装配，系统检测到Department有个属性employee没指定值，而有个bean的id又刚好叫employee，就拿来用了。


二、autowire="byName"同理是根据类型自动装配，bean的id就可以随便了，当然如果xml配置了多个此类型的bean，则没法匹配，会报错

<bean id="department" class="com.beans.Department" autowire="byType">
        <property name="name" value="财务部"/>
    </bean>
    
    <bean id="xx" class="com.beans.Employee">
        <property name="name" value="蔡文姬"/>
    </bean>

三、autowire="constructor"的意思就是指i，没配值的属性，系统会去找有没有对应的构造函数

public class Department {
    private String name;
    private Employee employee;
    
    
    public Department(Employee employee) {//给employee注入值，要求构造函数中，只能这个能给employee注入值
        this.employee = employee;
    }

<bean id="department" class="com.beans.Department" autowire="constructor">
        <property name="name" value="财务部"/>
    </bean>
    
    <bean id="xx" class="com.beans.Employee">
        <property name="name" value="蔡文姬"/>
    </bean>

四、autowire="default"

<beans
    xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation=
    "http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"
    default-autowire="byName"
    >
    
    <bean id="department" class="com.beans.Department" autowire="default">
        <property name="name" value="财务部"/>
    </bean>
    
    <bean id="employee" class="com.beans.Employee">
        <property name="name" value="蔡文姬"/>
    </bean>
    
</beans>

default-autowire="byName"指定的意思是，以下所有autowire="default"的bean都采用autowire="byName"