Spring overloaded constructor injection

问题

This is the code :

public class Triangle {


private String color;
private int height;


public Triangle(String color,int height){
    this.color = color;
    this.height = height;
}

public Triangle(int height ,String color){
    this.color = color;
    this.height = height;
}

public void draw() {
    System.out.println("Triangle is drawn , +
            "color:"+color+" ,height:"+height);
}

}

The Spring config-file is :

 <bean id="triangle" class="org.tester.Triangle">
    <constructor-arg value="20" />
    <constructor-arg value="10" />
</bean>

Is there any specific rule to determine which constructor will be called by Spring ?

回答1:

Here, the first argument will be matched to the first parameter of each method and then the parameter will be matched.

I would suggest the solution below to help remove ambiguity

If you want to call your first constructor use

<bean id="triangle" class="org.tester.Triangle">
<constructor-arg type="int"  value="20" />
<constructor-arg type="java.lang.String"  value="10" />
</bean>

If you want to call your second constructor use

<bean id="triangle" class="org.tester.Triangle">
    <constructor-arg type="java.lang.String"value="20" />
    <constructor-arg   type="int"  value="10" />
</bean>

So that resolves the ambiguity

EDIT :-

Please read more about this problem here.

回答2:

I don't believe so. Note that you can type the arguments e.g:

<bean id="triangle" class="org.tester.Triangle">
    <constructor-arg type="int" value="20" />
    <constructor-arg value="10" />
</bean>

which would remove the confusion in this scenario.

回答3:

Based on tests for Spring 3.1.0, the second constructor will be used. I don't know why, the documentation didn't give any definitive answer.

Bitbucket code To test, run Main class, it will output String FIRST or SECOND, depending which constructor will be used to create Triangle object.

来源：https://stackoverflow.com/questions/13864787/spring-overloaded-constructor-injection

标签

java

Spring

constructor-injection