Jakarta Commons Cookbook

7.8. Using Composite Configuration

Problem

Your application calls for a multilayered configuration where a set of default properties can be selectively overridden by local or user configuration preferences.

Solution

Create a configuration.xml file that contains references to multiple properties files, and pass this file to a ConfigurationFactory. A ConfigurationFactory will then return a Configuration implementation that obtains configuration parameters from multiple properties file.

Table 7-1 lists configuration properties for an application. A global configuration layer defines default values for configuration parameters. A local configuration layer allows you to customize the behavior of a system at a particular site, and the user configuration layer refines configuration parameters for a specific user. When an application retrieves the value of “name,” the user layer’s value of “Sean” overrides the global layer’s value of “Default User.”

Table 7-1. Three layers of configuration

Property	Global	Local	User
threads.max	50	30
threads.min	20		1
timeout	15.52
interactive	TRUE
color	red		black
speed	50	55	75
name	Default User		Sean

Properties are stored in three separate files shown in Examples Example 7-2 (global.properties), Example 7-3 (local.properties), and Example 7-4 (user.properties).

Example 7-2. global. properties

threads.max=50
threads.min=2
timeout=15.52
interactive=true
color=red
speed=50
name=Default User

Example 7-3. local .properties

# Overrides ...