Detailed explanation of the Commons Digester framework in the Java Class Library

Commons Digest is a Java class library that provides a simple way to analyze the XML document and map it to the Java object.It can correspond to the attributes of the XML document with the attributes of the Java object, thereby realizing the conversion of XML to Java objects. Using Commons Digester can easily process the analysis and processing of XML documents without manually writing a tedious analysis code.The following will introduce some key concepts and usage of the Commons Digestter. 1. DIGESTER object: The DIGESTER object is the core category of Commons Digest.It is the main tool for analyzing XML documents and converting it into Java objects.You can set the analysis rules through the DIGESTER object, add an analytical event monitor, and perform the parsing operation. The following is an example code that demonstrates how to create a Digest object and perform basic configuration: Digester digester = new Digester(); // Set the rules of the XML document to be parsed digester.addObjectCreate("root", RootObject.class); digester.addSetProperties("root"); digester.addSetNext("root/child", "addChild", ChildObject.class); // Add an analytical event monitor digester.addCallMethod("root/child/grandchild", "addGrandChild", 2); digester.addCallParam("root/child/grandchild", 0, "name"); digester.addCallParam("root/child/grandchild", 1, "value"); In the above code, the Java object corresponding to the root node is specified through the `adDObjectCreate` method, and the attribute value of the root node is set to set the attribute value of the root node. 2. Analysis rules: The analysis rules are used to configure the behavior of the DIGESTER object to analyze the XML document.You can set the analysis rules through a series of methods, such as: -` ADDObjectCreate (Pattern, ClassName) `: Specify the name of the Java object created by the Pattern matching node when parsing. -` ADDSETPROPERTIES (Pattern) `: Set the attribute value of the node matching node in the Pattern to the corresponding properties of the current Java object. -` ADDSETNEXT (Pattern, MethodName, ClassName) `: The Java object corresponding to the node matched with the pattern is used as the method parameter, and the MethodName method of the current Java object is called. -` ADDCallMethod (Pattern, MethodName, ParamCount) `: Specify the corresponding method of node matching node matching. -` ADDCallParam (Pattern, Paramindex, Paramname) `: Specify the parameters of the corresponding method of the node matching of the pattern matching. By using these methods, complex analysis rules can be constructed to meet the analysis needs of different XML documents. 3. Analyze the event monitor: You can capture events in the parsing process by adding an analytical event monitor to perform customized operations in specific scenarios.Common analysis event monitors include `Rule`,` Rulesbase` and `Ruleset`. -` Rule`: Analyze the rules, rewriting the method by inheriting the `Rule` class and rewriting it, you can perform a customized parsing operation. -`Rulesbase`: rule set to manage multiple analytical rules. -` Ruleset`: Rules set to manage a group of related analytical rules. These analysis events can be added to the Digest object to achieve control of the XML document analysis process. Summarize: This article details the COMMONS DIGESTER framework in the Java library.Through the flexible combination of Digester objects, analysis rules, and analysis of event monitoring, it can easily realize the conversion of XML documents to Java objects.This makes processing XML data simple and easy to maintain.In the actual development process, you can configure and use the Commons Digerster according to specific needs to improve development efficiency.