java - How to make spring inject value into a static field

Question

I know this may looks like a previously asked question but I'm facing a different problem here.

I have a utility class that has only static methods. I don't and I won't take an instance from it.

public class Utils{
    private static Properties dataBaseAttr;
    public static void methodA(){

    }

    public static void methodB(){

    }
}

Now I need Spring to fill dataBaseAttr with database attributes Properties.Spring config is:

<?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-3.0.xsd">

<util:properties id="dataBaseAttr"
        location="file:#{classPathVariable.path}/dataBaseAttr.properties" />
</beans>

I already done it in other beans but the problem here in this class (Utils) isn't a bean, And if I make it a bean nothing changes I still can't use the variable since the class will not be instantiated and variable always equals null.

Answer 1

You have two possibilities:

1. non-static setter for static property/field;
2. using org.springframework.beans.factory.config.MethodInvokingFactoryBean to invoke a static setter.

In the first option you have a bean with a regular setter but instead setting an instance property you set the static property/field.

public void setTheProperty(Object value) {
    foo.bar.Class.STATIC_VALUE = value;
}

but in order to do this you need to have an instance of a bean that will expose this setter (its more like an workaround).

In the second case it would be done as follows:

<bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="staticMethod" value="foo.bar.Class.setTheProperty"/>
    <property name="arguments">
        <list>
            <ref bean="theProperty"/>
        </list>
   </property>
</bean>

On you case you will add a new setter on the Utils class:

public static setDataBaseAttr(Properties p)

and in your context you will configure it with the approach exemplified above, more or less like:

<bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="staticMethod" value="foo.bar.Utils.setDataBaseAttr"/>
    <property name="arguments">
        <list>
            <ref bean="dataBaseAttr"/>
        </list>
   </property>
</bean>