When a Struts application is initialized, one of the first things that it must do is to read and parse the configuration file, which, as you’ve seen in this chapter, is in XML. The Digester component is a separate Jakarta project made up of several classes that read XML files and create and initialize Java objects based on those files.
The Digester component uses a set of rules, written as a Java class, to invoke callback methods. These methods instantiate and populate the objects with data read from the Struts configuration file.
The Struts framework uses the Digester to parse the configuration
files and to create the necessary configuration objects within the
org.apache.struts.config package. The rules that
the Digester uses for Struts are contained within the
org.apache.struts.config.ConfigRuleSet class.
There is little need to modify the ConfigRuleSet
class unless you need to extend the configuration file. If this is
necessary for your application, you should view the documentation for
the Digester component before you get started. This can be found at
http://jakarta.apache.org/
commons/digester.html.
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