Question

I have a Spring 3.1 application, and I try to use a system variable in the context files. The variable “JAVA_MY_ENV” is defined on my System (on Windows, it is in the “System variables”, from the control panel).

In web.xml, I can use it as a variable and it works, it is successfully replaced by the actual value of the variable (let’s say “electrotype”) :

<listener>
    <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
</listener> 
<context-param>
    <param-name>log4jConfigLocation</param-name>
    <param-value>classpath:log/${JAVA_MY_ENV}.log4j.properties</param-value>
</context-param>

I can also use it in my main “bean” context, to do an import, and it also works :

<?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:context="http://www.springframework.org/schema/context"       
        xmlns:tx="http://www.springframework.org/schema/tx" 
        xsi:schemaLocation="http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
                            http://www.springframework.org/schema/context
                            http://www.springframework.org/schema/context/spring-context-3.1.xsd
                            http://www.springframework.org/schema/tx
                            http://www.springframework.org/schema/tx/spring-tx-3.1.xsd">

    <!-- (...) -->

    <import resource="classpath:spring/app-config.xml" />
    <import resource="classpath:spring/env/context-env-${JAVA_MY_ENV}.xml" />

</beans>

But In “app-config.xml”, one of my other context file, I try this and it doesn’t work :

<?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:context="http://www.springframework.org/schema/context"       
        xmlns:tx="http://www.springframework.org/schema/tx" 
        xsi:schemaLocation="http://www.springframework.org/schema/beans
                            http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
                            http://www.springframework.org/schema/context
                            http://www.springframework.org/schema/context/spring-context-3.1.xsd
                            http://www.springframework.org/schema/tx
                            http://www.springframework.org/schema/tx/spring-tx-3.1.xsd">

    <bean id="appConfiguration" class="com.xxx.app.AppConfiguration">
        <constructor-arg value="${JAVA_MY_ENV}" />
    </bean>

</beans>

The com.xxx.app.AppConfiguration receives the String “${JAVA_MY_ENV}” as the constructor parameter, not the interpreted value of it!

I’m not sure to understand where the ${} variables are interpreted and where they are not.

Is there a way I can pass the interpreted ${JAVA_MY_ENV} value to my com.xxx.app.AppConfiguration constructor?

Answer 1

As of 3.0 in Spring you should be to inject values into properties

@Value("#{ systemProperties['JAVA_MY_ENV'] }") 
private String myVar;

or

<property name ="myVar" value="#{systemProperties['JAVA_MY_ENV']}"/>

Alternatively you can look into using the PropertySourcesPlaceholderConfigurer or similar class. Creating this will tell spring how to look for variables. Often i make a number of property files as well so that environment and internal property file values are available to the app. e.g.

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="locations">
    <list>
        <value>classpath:someprops.properties</value>
    </list>
  </property>
  <property name="ignoreResourceNotFound" value="true" />
  <property name="searchSystemEnvironment" value="true" />
  <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />

A key element in the above example is the “searchSystemEnvironment” being set to true. This tells spring to use env variables (which is what you want)