Adding a custom PropertySource to the environment using EnvironmentPostProcessor

In cases where the enterprise is already using a particular configuration system, custom written or off the shelf, Spring Boot provides us with a facility to integrate this into the application via the creation of a custom PropertySource implementation.

How to do it...

Let's imagine that we have an existing configuration setup that uses a popular Apache Commons Configuration framework and stores the configuration data in XML files:

1. To mimic our supposed pre-existing configuration system, add the following content to the dependencies section in the build.gradle file:

dependencies { 
  ... 
  compile project(':db-count-starter') 
  compile("commons-configuration:commons-
     configuration:1.10") 
  compile("commons-codec:commons-codec:1.6") 
  compile("commons-jxpath:commons-jxpath:1.3") 
  compile("commons-collections:commons-collections:3.2.1") 
  runtime("com.h2database:h2") 
  ... 
} 

2. Follow this up by creating...