Composition of configurations
The SettingsCore class extends CompositeConfiguration, using the facilities provided by this class to produce an aggregated configuration from three sources in the following order of precedence:
- System properties
- (optional) Stored properties, typically from a properties file
- (optional) Default values, typically specified in the enumeration
Declaring stored properties
To specify stored properties for your configuration, override one of following methods:
getStoredConfig- Your implementation returns a populated Configuration object.
getInputStream- Your implementation returns an input stream supplying key/value pairs.
getSettingsUrl- Your implementation returns the URL from which to load your settings.
getSettingsPath- Your implementation returns the path from which to load your settings.
NOTE: These methods are listed in order of evaluation, which stops at the first non-null response.
NOTE: Typical implementations override
getSettingsPath, which will support most scenarios.
NOTE: Stored properties are declared in Apache's extended syntax. See PropertiesConfiguration for details.
NOTE: By overriding the
getStoredConfigmethod, you're able to incorporate any arbitrary Configuration object you need into your settings - including another CompositeConfiguration object.
Specifying default values
Two methods have been provided for you to supply default values for your configuration:
- Specify default values as arguments of the constant declarations in your settings enumeration and override the
SettingsAPI.valmethod. Specifying 'null' for a setting's default value indicates that no default exists.
- Alternatively, you can override the
getDefaultsmethod with your own implementation.
NOTE: For settings collections with no default values, you can eliminate unnecessary processing in the core API by overriding
getDefaultswith a method that simply returns 'null'.
Declaring configuration settings
Implementations of SettingsCore supply a context-specific enumeration (which extends Enum<T>) to provide the collection of settings needed in this context. This enumeration must implement the SettingsAPI interface to provide clients with a common method for retrieving configuration keys and to give the core settings implementation access to the constants and default values of the enumeration.
For example implementations of SettingsCore, check out this project's units tests. These demonstrate all of the major features of the API, including:
- Declaration of settings and default values
- Declaration and formatting of backing files
- Extraction of typed data
- Declaration of lists of values
- Overrides of stored and default values
- Configurable inclusion of sub-configurations