In -depth understanding of the technical principles of Apache Commons Digester framework

Apache Commons Digest is a powerful Java framework that is used to analyze XML documents and convert it to Java objects.It specifies how XML elements are mapped to the Java object by using a set of rules, and uses the stack data structure to track the analysis status.This article will explore the technical principles of Apache Commons Digerster and provide some Java code examples to illustrate its usage. The working principle of the Apache Commons Digester is as follows: 1. Create the Digestter object: First of all, we need to create a Digetter object that will be used to analyze XML documents and convert it to Java objects.You can use the default constructor to create a Digest object, or it can be created through the static factory method of DIGESTER. Digester digester = new Digester(); 2. Configuration rules: Next, we need to configure the rules of the DIGESTER object to specify how to map the XML element to the Java object.The rules are composed of a set of rules and corresponding rules.The rule mode is an XPATH expression for matching XML elements, while the rules define the operation of converting matching elements into Java objects. digester.addRule("bookstore/book", new ObjectCreateRule(Book.class)); digester.addRule("bookstore/book/title", new SetNextRule("setTitle")); digester.addRule("bookstore/book/author", new BeanPropertySetterRule("author")); The above code fragment demonstrates how to use the rules of the DIGESTER to map the XML element to the Java object.In this example, when DIGESTER meets the `` BookStore> <book> `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `` `they create a BOOK object.Then, when encountering the `<Title>` `element, it calls the` settitle () method of the Book object and pass the content of the element as the parameter to the method.When encountering the `` AUTHOR> `` element, it will set the corresponding attributes using the `setAnceHor () method of the Book object. 3. Analyze XML document: Once the rules are configured, we can use the Digerster object to parse the XML document. Bookstore bookstore = digester.parse(new File("bookstore.xml")); The above code fragment demonstrates how to use the `PARSE ()` method of DIGESTER to analyze the XML document and convert it to the Java object.After the analysis is completed, we will get a Bookstore object that contains data extracted from XML documents. To sum up, the technical principle of Apache Commons Digest is to define the mapping relationship of XML elements to Java objects by configure a set of rules, and use the stack data structure to track the analysis state.When Digestter encounters the XML element of the matching rules mode, it performs the corresponding rule operation to convert the content of the element to the attribute value of the Java object.In this way, we can easily extract data from the XML document and convert it to the Java object to further process it in the application. It is hoped that the content provided in this article can help readers in depth understanding the technical principles of the Apache Commons Digest frame, and can use the Java code example to practice when needed.