-- Expanding Properties within Checkstyle configuration files --

Checkstyle contains a feature that lets you define module properties in a way that they can expanded dynamically when the configuration is loaded.
Such a property is defined using the well known ${property_name} notation.

Normally these properties are resolved from command line or ant properties.
Of course this does not work within the plug-in so using a checkstyle configuration containing such expandable properties will probably fail.

But as you might have thought there are some features in place to help you out in this case.

When a Check Configuration is set up the plugin will check the Checkstyle configuration file for unresolved properties.
When found the plugin will warn you that this configuration cannot be used until those properties can be resolved.
To resolve such properties you have a variety of options.

Built-in properties

First there are some properties that are automatically expanded by the plug-in:

  • ${basedir} - gets mapped to the current project directory

  • ${project_loc} - same as ${basedir}

  • ${workspace_loc} - gets mapped to the current Eclipse workspace directory

  • ${config_loc} & ${samedir} - get mapped to the directory the configuration file lies in

Resolving from .properties file

If you have more properties that need to be expanded there is another feature for you.

Using External, Remote or Project Relative Configuration you can write the properties you need to be expanded into a .properties file that lies in the same directory as the configuration file and has the same name.
For instance:

can resolve properties defined in

Expandable properties within your configuration file will then be resolved from the corresponding .properties file.

Resolving from Classpath Variables and Environment properties

New in 4.1.0 is that you can resolve properties from Classpath Variables (set up in workspace preferences) and from Environment Properties.
Note that these need to be passed into the VM Eclipse runs on using the famous -D parameter.

Additional properties configured with the Check Configuration

If all this stuff doesn't suit your needs there is another option for you.
Reintroduced in 4.1.0 is support for storing properties with the Check Configuration setup.
You might have already noted the new Additional properties... button located in the lower left of a Check Configuration setup dialog.
Pressing this button will lead you to another dialog where you can input properties and their values
To aid in this task the plugin offers to find unresolved properties for you.
Properties set up here will be stored with the Check Configuration data, for Global Configurations within the plugins workspace state location, for Local Configurations within the .checkstyle file.

Note that the plug-in supports 'property chaining' to let you use 'properties within properties'.
With this feature you can write something like this in your .properties file:

Using ${property2} in your checkstyle configuration will then be resolved to: abcdef