The technical principles of Apache Commons Digest Framework in the Java class library

Apache Commons Digester is an open source framework for analysis of XML documents. It provides a simple and flexible way to convert XML documents into Java objects.This article will explore the technical principles of the DIGESTER framework and give the corresponding Java code example. Overview of ## Digester framework The DIGESTER framework is based on the event drive model. It can resolve XML documents into events one by one, and then perform corresponding operations according to the pre -configured rules, such as creating Java objects and calling methods.It uses the Java reflection mechanism to automatically map the elements and attributes of XML to the attributes and methods of the Java object. ## Digester framework configuration Before using the Digester framework, we need to define some rules to tell it how to analyze XML documents.DIGESTER uses XML configuration files to describe these rules, and the configuration file defines a series of rules and processors.Here are a simple DigEster configuration file example: <digester-rules> <pattern value="rootNode"> <object-create-rule classname="com.example.RootObject" /> <set-properties-rule /> </pattern> <pattern value="rootNode/childNode"> <object-create-rule classname="com.example.ChildObject" /> <set-properties-rule /> <set-next-rule methodname="addChild" /> </pattern> </digester-rules> In the above configuration file, two rules are defined.The first mode is "ROOTNODE", which specifies the Java object category named "com.example.rootObject" to create it and automatically set its attributes.The second mode is "ROOTNODE/ChildNode", which specifies the Java object class named "com.example.childObject". It will also automatically set its attributes and call the "Addchild" method to add the object to the father object to the father objectmiddle. ## DIGESTER framework core category The core category of the DIGESTER framework is `ORG.APACHE.COMMONS.Digerster.digester`.The basic steps of using the Digester framework are as follows: 1. Create the Digestter object: `Digestter Digerster = New Digest ();` 2. Configure the DIGESTER object: `Digester.addruleset (New RuleSetDigerster (Rules)); 3. Analyze the XML document: `Object Result = Digester.parse (InputStream);`, the analysis results will return a Java object. Example of ## DIGESTER framework The following uses a simple example to illustrate the use of the DIGESTER framework: import org.apache.commons.digester.Digester; import org.xml.sax.SAXException; import java.io.IOException; public class DigesterExample { public static void main(String[] args) { Digester digester = new Digester(); digester.addRuleSet(new RuleSetDigester(rules)); try { Object result = digester.parse(inputStream); // Treatment the analytical results } catch (IOException | SAXException e) { e.printStackTrace(); } } } In the above sample code, we first created a DIGESTER object and configured the rules, and then resolved the XML document through the `PARSE` method. The analysis results will be stored in the` Result` variable.We can customize the processing logic of the analytical results according to actual needs. ## in conclusion The Apache Commons Digest Framework has a function of converting XML documents into Java objects by parsing the XML document and performing pre -defined rules.It is flexible and easy to use, suitable for various types of XML analysis scenarios.By learning and using the DIGESTER framework, we can process XML data more efficiently.