spring 构造器注入 及index

 

bean:

@Data
public class Food {
    private String color;
}

 

@Data
public class Cat {
    private String catName;
    private Food food;

    // 构造方法1
    public Cat(String catName, Food food) {
        this.catName = catName;
        this.food = food;
    }
    
    // 构造方法2
    public Cat(Food food, String catName) {
        this.catName = catName;
        this.food = food;
    }
}

 

constructor不管是什么顺序，都是走了构造方法1： 

这两个构造器都会进构造方法1：    

    <bean id="food1" class="com.readspring.bean.Food" p:color="yellow"/>   

 
    <!-- cat bean -->

    <bean id="cat1" class="com.readspring.bean.Cat">
        <constructor-arg name="food" ref="food1" />
        <constructor-arg name="catName" value="tom" />
    </bean>



或者对cat调换constructor-arg顺序：
    <bean id="cat1" class="com.readspring.bean.Cat">
        <constructor-arg name="catName" value="tom" />
        <constructor-arg name="food" ref="food1" />
    </bean>

 

当希望走构造方法2时候，就需要使用index 指定构造器参数顺序

    <bean id="cat1" class="com.readspring.bean.Cat">
        <constructor-arg name="catName" index="1" value="tom" />
        <constructor-arg name="food" index="0" ref="food1" />
    </bean>

使用index后果然进了构造方法2：