Spring Override

This library provides an XML namespace handler that allows for overriding, extending or modifying beans in a modular Spring environment. The code was originally written by Felix Gnass and Carsten Woelk back in 2007 as part of the riot content management system. So all credits go to them.

As Pivotal has abandoned the Spring DM project I figured that riot's pragmatic override feature is still valuable to many developers who try to modularize their Spring projects. So I decoupled the feature and moved it into its own project. Although this library comes with a Spring 4.1 dependency, it should also work with older version. Here is a very simple example how to use it:

If you are using Maven, include the dependency into your pom.xml

<dependency>
    <groupId>com.apporiented</groupId>
    <artifactId>spring-override</artifactId>
    <version>${spring-override.version}</version>
</dependency>

Make sure you include the application context files of all your modules. A web project could specify the context locations like this:

<context-param>
   <param-name>contextConfigLocation</param-name>
   <param-value>classpath*:META-INF/spring/application-context-*.xml</param-value>
</context-param>

Let's assume you have the following configuration in your main project (application-context-main.xml):

<beans
        xmlns="http://www.springframework.org/schema/beans"
        xmlns:override="http://www.apporiented.com/schema/spring/override"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.apporiented.com/schema/spring/override
        http://www.apporiented.com/schema/spring/override.xsd">
        
    <bean id="bean" class="com.apporiented.spring.override.OverrideTestBean">
        <property name="string" value="Original" />
        <property name="list">
            <list>
                <value>string1</value>
                <value>string2</value>
                <value>string3</value>
            </list>
        </property>
        <property name="map">
            <map>
                <entry key="key" value="original" />
            </map>
        </property>
    </bean>
</beans>

Now a submodule can change application's behavior by providing a configuration such as (application-context-sub.xml)

<beans
        xmlns="http://www.springframework.org/schema/beans"
        xmlns:override="http://www.apporiented.com/schema/spring/override"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.apporiented.com/schema/spring/override
        http://www.apporiented.com/schema/spring/override.xsd">

    <override:properties ref="bean">
        <property name="string" value="overridden" />
    </override:properties>

    <override:add ref="bean" property="list" append="true">
        <value>string4</value>
        <value>string5</value>
    </override:add>

    <override:put ref="bean" property="map">
        <entry key="key" value="overridden" />
    </override:put>

</beans>

The bean overriding occurs at a very early stage of the Spring initialization process. Hence, all autowired dependencies to bean will see the modifications made by the sub module.