Can I use an Environment variable based location for Spring FileSystemResource?

Question

I have a requirement to have all our properties files be stored in a directory. The location of this directory should be stored in a system environment variable. In my appli

Answer 1

In Spring.Net we have got the IVariableSource interface and PropertyPlaceholderConfigurer which are able to retrieve values from environment variables. Maybe there is something similar in the Spring Framework for Java?

Edit: I think I found the corresponding java bean which is named PropertyPlaceholderConfigurer as well in the java docs.

Answer 2

UPDATE

We later upgraded to Spring 3.0.X and we were able to take advantage of the spring expression language. Our approach simplified from three beans to the following snippet:

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="locations">
    <list>
        <value>classpath:defaults.properties</value>
        <value>file:/a/defined/location/project.properties</value>
        <value>file:${AN_ENV_CONFIGURED_DIR}/project.properties</value>
    </list>
  </property>

  <property name="ignoreResourceNotFound" value="true" />
  <property name="searchSystemEnvironment" value="true" />
  <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />
</bean>

This allowed us to have either a development (the first defaults) statically well known location, or a deployed location configured via env variables. The configurer processes these in order (i.e. the deployed takes precedence over the defaults).

OLD

I ended up going with a non programmatic approach. I used a MethodInvoker to retrieve the environment value. I was able to then pass that into the FileSystemResource.

<bean id="configPath" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean" >
    <property name="targetClass" value="java.lang.String" />
    <property name="staticMethod" value="java.lang.System.getenv" />
    <property name="arguments">
        <list>
            <value>NAME_OF_VARIABLE</value>
        </list>
    </property>
</bean>

Answer 3

while I note that the question required 2.5.x, it's worth pointing out that Spring 3's EL support (available since Nov 2009) would've made short work of this sort of thing

@Value("#{ systemProperties['user.home'] }") 
private String userHome ;

or

<property name = "userHome" value ="#{ systemProperties['user.home'] }"/>

Answer 4

Example:

Start you app with -DDA_HOME=c:\temp

c:\temp must contain directory called "config"

In c:\temp\config you have file app.properties (for example)

Extend the Spring loader:

public class Loader extends org.springframework.beans.factory.config.PropertyPlaceholderConfigurer{

    private String appHome;

    public void setAppHome(String appHome) {
        this.appHome = appHome;
    }

    @Override
    public void setLocation(Resource location) {
        if(appHome==null){
            throw new RuntimeException("You must specify VM property DA_HOME, this directory must contain " +
                    "another directory, called config, inside the config directory app.properties " +
                    "file must be found with the configuration properties");
        }
        String configurationDirectory = appHome + System.getProperty("file.separator") + "config";
        String fileName = location.getFilename();
        Resource file = new FileSystemResource( configurationDirectory + System.getProperty("file.separator")+ fileName);
        super.setLocation(file);
    }
}

Specify the new loader and its configuration base:

    <bean id="placeholderConfig"    class="your.Loader">
        <property name="appHome" value="#{systemProperties['DA_HOME']}"/>
        <property name="location" value="app.properties" />
    </bean>

Answer 5

You could always extend the FileSystemResource (i.e. PropertiesFileResource) that would initialize itself by taking prepending the property file location system property to the file path.