Java – spring: set property of one bean by reading the property of another bean

dependency-injectionjavaspring

Is it possible to set the property of one bean by reading the property of another bean? For instance, suppose I had:

class A {
   void setList(List list);
}

class B {
   List getList();
}

I would like Spring to instantiate both classes, and call A's setList method, passing in the result of calling B's getList method. The Spring configuration might look something like:

<bean id="b" class="B"/>
<bean id"a" class="A">
    <property name="list" ref="b" ref-property="list"/>
</bean>

Alas, this made-up XML does not work.

Why not just inject B into A? Because I do not want to introduce the extra dependency. A is only dependent List, not on B.

Best Answer

in addition to @Kevin's answer if you are using spring 3.0 it is possible to do this with the new spring expression language

<bean id="a" class="A">
    <property name="list"
        value="#{b.list}"/>
</bean>

spring 3.0 documentation

Related Solutions

Java – How to call one constructor from another in Java

Yes, it is possible:

public class Foo {
    private int x;

    public Foo() {
        this(1);
    }

    public Foo(int x) {
        this.x = x;
    }
}

To chain to a particular superclass constructor instead of one in the same class, use super instead of this. Note that you can only chain to one constructor, and it has to be the first statement in your constructor body.

See also this related question, which is about C# but where the same principles apply.

Java – How to define a List bean in Spring

Import the spring util namespace. Then you can define a list bean as follows:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="http://www.springframework.org/schema/beans
                    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
                    http://www.springframework.org/schema/util
                    http://www.springframework.org/schema/util/spring-util-2.5.xsd">


<util:list id="myList" value-type="java.lang.String">
    <value>foo</value>
    <value>bar</value>
</util:list>

The value-type is the generics type to be used, and is optional. You can also specify the list implementation class using the attribute list-class.

Best Answer

Related Solutions

Java – How to call one constructor from another in Java

Java – How to define a List bean in Spring

Related Topic