The technical principles of Apache Commons Digest frame in the Java library analysis

Apache Commons Digester is a Java class library that is used to read data from XML files and map it into the Java object.It uses rules in XML files to analyze and mappore data, thereby providing a simple and flexible way to process XML data. The working principle of the DIGESTER can be simply summarized as the following steps: 1. Create a DIGESTER object: First of all, you need to create a DIGESTER object for configuration and processing XML data.You can create objects through Digester's constructor. 2. Configure the DIGESTER rules: Next, you need to configure the rules for the Digester object to tell it how to analyze XML data.The DIGESTER rules are composed of some rules instances, and each instance defines the conditions and operations of a rule. 3. Start parsing XML: By calling the analysis method of the DIGESTER object, you can start parsing XML files.DIGESTER reads XML files in line in accordance with the rules and process data according to the definition of the rules. 4. Matching rules and operations: When Digetter reads each line in the xml file, it will match the rules of configuration.If the rules match successfully, the DIGESTER will perform corresponding operations, such as creating objects, calling methods, setting attributes, etc. 5. Map the data to the Java object: Digester will map the data obtained into the Java object according to the rules when performing operations.The data mapping can be implemented by setting the attribute value of the object, calling the object method, etc. Below is an example of using Apache Commons Digester to analyze XML data: public class Person { private String name; private int age; // getters and setters @Override public String toString() { return "Person [name=" + name + ", age=" + age + "]"; } } public class XmlParser { public static void main(String[] args) throws Exception { Digester digester = new Digester(); // Configuration rules digester.addObjectCreate("persons/person", Person.class); digester.addSetProperties("persons/person"); digester.addSetNext("persons/person", "add"); // Analyze XML file List<Person> persons = (List<Person>) digester.parse(new File("data.xml")); // Output resolution results for (Person person : persons) { System.out.println(person); } } } In the above example, we first created a Digest object, and then configured three rules: creating a Person object, setting the attributes of the Person object, and adding the Person object to a list.Then by parsing the XML file, the DIGESTER will map the XML data to the Person object according to the configuration rules and store the parsing Person object in the list.Finally, we traversed the list and output the resolution results. In general, the Apache Commons Digester framework is a powerful and easy -to -use tool. It provides a convenient way to analyze and map XML data to Java objects, thereby simplifying the XML data processing process.