Reading Configuration Values from a Component

Once you have the application configured so that administrators can configure it in System Settings, you might be wondering how to read the configuration from your application’s Java code.

The answer is that there are several ways. Which one you use depends on the context from which the configuration must be read:

1. From any Component class

2. From an MVC portlet’s JSP

3. From an MVC portlet’s Portlet class

4. From a non-Component class

This tutorial shows the first usage, reading the configuration from a Component class.

Reading Configurations from a Component Class

1. First set the configurationPid Component property as the fully qualified class name of the configuration class:

   @Component(configurationPid = "com.liferay.dynamic.data.mapping.form.web.configuration.DDMFormWebConfiguration")
   

2. Then provide an activate method, annotated with @Activate to ensure the method is invoked as soon as the Component is started, and @Modified so it’s invoked whenever the configuration is modified.

   @Activate
   @Modified
   protected void activate(Map<String, Object> properties) {
       _formWebConfiguration = ConfigurableUtil.createConfigurable(
           DDMFormWebConfiguration.class, properties);
   }
   
   private volatile DDMFormWebConfiguration _formWebConfiguration;
   

   The activate() method calls the method ConfigurableUtil.createConfigurable() to convert a map of the configuration’s properties to a typed class, which is easier to handle. The configuration is stored in a volatile field. Don’t forget to make it volatile to prevent thread safety problems.

3. Once the activate method is set up, retrieve particular properties from the configuration wherever they’re needed:

   public void orderCar(String model) {
       order("car", model, _configuration.favoriteColor);
   }
   

   This is dummy code: don’t try to find it in the Liferay source code. The String configuration value of favoriteColor is passed to the order method call, presumably so that whatever model car is ordered will be ordered in the configured favorite color.

Note: The bnd library also provides a class called aQute.bnd.annotation.metatype.Configurable with a createConfigurable() method. You can use that instead of Liferay’s com.liferay.portal.configuration.metatype.bnd.util.ConfigurableUtil without any problems. Liferay’s developers created the ConfigurableUtil class to improve the performance of bnd’s implementation, and it’s used in internal code. Feel free to use whichever method you prefer.

With very few lines of code, you have a configurable application that dynamically changes its configuration, has an auto-generated UI, and uses a simple API to access the configuration.