Configuration utils: EnvironmentConfiguration extension to support UPPER_SNAKE_CASE for environment variables

[wajda]

Problem

The existing org.apache.commons.configuration.EnvironmentConfiguration provides access to the environment variables via an abstract Configuration API. However the problem is that while the more abstract Configuration operates with properties (that in turn implies a dot-separated key notation considered a standard in Java world) the EnvironmentConfiguration preserves original environment variable names which is usually an upper-cased snake notation. This discrepancy spill out the particular class implementational details over its API, and logically couples the caller to the implementation.

One of the use-cases where the issue pops is CompositeConfiguration. Combining EnvironmentConfiguration with almost any other Configuration implementation in one bucket won't work as expected.

Example:

val conf = new CompositeConfiguration(asList(
  new EnvironmentConfiguration,
  new SystemConfiguration,
  new JNDIConfiguration("java:comp/env")
))

conf.getString("java.vm.vendor")      should not be null // OK - defined in JVM system properties as "java.vm.vendor"
conf.getString("env.jdbc.datasource") should not be null // OK - defined in JNDI as "java:comp/env/jdbc/datasource"
conf.getString("scala.home")          should not be null // FAILS !!!
conf.getString("SCALA_HOME")          should not be null // OK - defined in System environment, so I have to use a proper notation

Solution

Create an extension to the EnvironmentConfiguration that would respect domain naming convention for keys, so that calling

(new EnvironmentConfiguration).getString("scala.home") // would lookup for SCALA_HOME in system environment

Similarly to how it's done in JNDIConfiguration for instance.