Profiles in Spring Framework Configuration

2012-12-16

Profiles in Spring Framework Configuration

Spring is a perfect place to centralize your project's configuration. Afterall, that was it's initial purpose.

Sooner or later, you will want to parametrize your configuration. That means, by setting one parameter, e.g. profile, many configuration details should change.

I'll show you how to do that.

Substitution in Values – `PropertyPlaceholderConfigurer`

You can read some properties from a file and use them to substitute some „variables“ in bean properties' values. A typical usage example is JDBC configuration – one for developement and other for release:

<!-- JDBC Datasource -->
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
  <property name="driverClassName" value="${jdbc.driver}" />
  <property name="url" value="${jdbc.url}" />
  <property name="username" value="${jdbc.username}" />
  <property name="password" value="${jdbc.password}" />
</bean>

Now you must specify a file where the values of these ${...}-enclosed variables, called placeholders, are defined. You can use more files, the later overriding the former.

Here we use properties/database.properties from the .jar to define „defaults“ and then override some properties in an external file.

<context:property-placeholder location="
  classpath:properties/database.properties,
  file:conf/database.properties" />

If you want to keep the possibility of removing the external file and relying solely on the defaults, you might use the ignoreResourceNotFound attribute:

<context:property-placeholder location="
  classpath:properties/database.properties,
  file:conf/database.properties" ignoreResourceNotFound="true" />

However, in Spring 2.x, only the location attribute is supported for <context:property-placeholder/> element (this shall probably work in Spring 3.0). So, you need to define it „old way“ – as a bean:

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="locations" value="
      classpath:properties/database.properties,
      file:conf/database.properties" />
  <property name="ignoreResourceNotFound" value="true" />
</bean>

Setting up a Profile – Parametrized Configuration

In the preamble, I promissed I'll show how to set up some basic profiling.

Profiles can be set up using the placeholders in the placeholder configuration itself – e.g. by setting location to file:conf/${profile}/nastaveni.properties. But where does the ${profile} come from, when we still don't have the properties from the files available?

Spring can substitute placeholders in the definitions of property placeholders using the system properties and evironment variables, that is, what is available from System.getProperty(String) and System.getenv(String).

So first, we define the system property, either as a JVM -D parameter, or programatically:

## in the command line:
$ java -Dprofile=testing

// Or in Java:
System.setProperty( "profile", "testing" );

Then we can set the bean up using all our weapons:

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="locations" value="
      classpath:properties/database.properties,
      file:nastaveni.properties,
      file:conf/${profile}/nastaveni.properties" />
  <property name="ignoreResourceNotFound" value="true" />
  <property name="ignoreUnresolvablePlaceholders" value="true" />
  <property name="searchSystemEnvironment" value="true" />
  <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />
</bean>

The searchSystemEnvironment and systemPropertiesModeName have reasonable defaults and can be ommited. For more information, see the PropertyPlaceholderConfigurer javadoc.

See also the oficial (and up-to-date) Spring guide to placeholders and overriding: 3.7.2. Customizing configuration metadata with BeanFactoryPostProcessors.

Overriding (or Overwriting) default values – `PropertyOverrideConfigurer`

When using PropertyPlaceholderConfigurer, you inherently must define the values at least once in some properties file. Sometimes you could assume that the defaults will be rarely needed to be overridden, so you might want to keep the defaults right in the custom beans' configuration in Spring's .xml.

That is possible with PropertyOverrideConfigurer. Simply configure your bean as usualy:

<bean  name="projectInfo" class="cz.dynawest.springtest.CoolProject">
  <property name="author" value="Ondřej Žižka" />
  <property name="maintainer" value="Ondřej Žižka" />
</bean>

Then, you can override some of the properties in a properties file. The syntax of the name is <bean-name>.<property-name>=<value>.

## newProjectInfo.properties
projectInfo.maintainer="Reese Witherspoon"

The final piece of the puzzle is to create a bean that will apply the value to the bean.

<context:property-override location="classpath:newProjectInfo.properties"/>

More information on overriding can be found in Spring Reference Documentation – 3.7.2.2. Example: the PropertyOverrideConfigurer or PropertyOverrideConfigurer JavaDoc.

Profiles in Spring Framework Configuration