Lately I'm working on Spring 3.0 hobby project in my spare time. Frequent readers of my blog or followers me on Twitter might think: Why plain Spring and not just Grails? So let me explain that first:
- I love Grails (and Groovy), and if I could make the decision I would use it on every project! But...
- I want to host my hobby project cheap, and even Amazon EC2/AWS is to expensive currently. So I decided to host my application on Google App Engine. And to be honest, Grails support for GAE is just alpha/beta state in my opinion (I hope it will change one day). So Grails was not an option.
- I've been coding Groovy and Grails for a while now and also doing commercial projects. But I have the feeling my basic Java and Spring knowledge might become a little bit rusty. And to face the facts, there is a change that one of my next clients will not use Groovy/Grails, but just Java and one of the 1,000,000 Java frameworks outhere. So with my hobby project I will be up to date with the latest Java and Spring 3.0 expertise!
But let's get back to the title of this post: ConfigSlurperPlaceholderConfigurer for Spring. In my hobby project I needed the concept of per environment configuration. Yes, in Grails you have it out-of-the-box but in Spring not.
I searched the web and found some interesting thoughts:
- RuntimeEnvironmentPropertiesConfigurer - A subclass of PropertyPlaceholderConfigurer which uses a specific config file based on a system property
- Configleon - Also an interesting mini framework for per environment configs
- GroovyPlaceholderConfigurer - A subclass of PropertyPlaceholderConfigurer which uses a Groovy ConfigSlurper
What I like about Grails' concept of per environment configuration is that you can define global config properties and just override them in a specific environment if needed. So if 90% of my properties are the same for each environment I don't need to specify them for all environment but just once.
This concept was not supported by the RuntimeEnvironmentPropertiesConfigurer, and also not by the GroovyPlaceholderConfigurer. I know the GroovyPlaceholderConfigurer uses a Groovy ConfigSlurper and this does support per environment configuration (Grails uses it!). So I decided to create a proper ConfigSlurperPlaceholderConfigurer which also supports different environments using a system property. At the end this is how my Spring config now looks:
Example XML context definition:
<bean class="org.springframework.beans.factory.config.ConfigSlurperPlaceholderConfigurer">
<property name="environment" value="#{systemProperties['runtime.environment']}" />
<property name="defaultEnvironment" value="production" />
<property name="location" value="/WEB-INF/config.groovy" />
</bean>
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName"><value>${dataSource.driverClassName}</value></property>
<property name="url"><value>${dataSource.url}</value></property>
<property name="username"><value>${dataSource.username}</value></property>
<property name="password"><value>${dataSource.password}</value></property>
</bean>
Example config.groovy:
dataSource {
driverClassName = "org.hsqldb.jdbcDriver"
username = "sa"
password = ""
}
environments {
development {
dataSource {
url = "jdbc:hsqldb:mem:devDB"
}
}
test {
dataSource {
url = "jdbc:hsqldb:mem:testDb"
}
}
production {
dataSource {
url = "jdbc:hsqldb:file:prodDb;shutdown=true"
password = "secret"
}
}
}I created a new issue in Spring JIRA to add this to core. If you are interested you can vote for the issue. It also contains the source code if you want to use it in your own project.
