The application and principle analysis of the Commons Digestter in the Java library
The application and principle analysis of the Commons Digestter in the Java library
Commons Digest is a widely used tool in the Java library. It implements the mapping of XML to Java objects, allowing developers to process XML data easier.This article will introduce the principles of Commons Digester and its application in the Java class library, and provide some Java code examples to explain.
Original analysis:
Commons Digestter is based on a technology called "rule mode".It analyzes XML data by defining a series of rules and converts it into Java objects.DIGESTER will listen to the incidents of XML documents, such as element start, element end and other events according to the definition of the rules, and perform specific operations when the corresponding events occur.These operations may include creating Java objects, setting object attribute values, and pressing the object into the stack.
Digest's working method can be briefly described as the following steps:
1. Create a DIGESTER instance.
2. Configure the rules set of DIGESTER, including defining object creation, attribute settings, method calling and other operations.
3. Call the PARSE () method of the DIGESTER and pass the XML data to be parsed.
4. Digester will read the event of the XML document in turn, and perform the corresponding operation according to the rules.
5. After the analysis is completed, you can get the generated Java object from the Digestter.
Application scenario:
Commons Digest is widely used in processing XML data in many Java applications.The following are examples of some application scenarios:
1. Configuration file analysis: Many Java applications use XML files as configuration files. Digester can help resolve configuration files and generate corresponding configuration objects.
2. Web application development: DIGESTER can be used to resolve XML requests and response data in web applications, and convert it to Java objects for processing.
3. Data mapping: If there is a file containing a large amount of xml format data, you can use Digestter to convert it to Java objects.
4. Test data generation: Digester can be used to generate test data. By defining the rules set, the test data is converted from XML format to Java object, thereby simplifying the test process.
Java code example:
Below is a simple Java code example, demonstrating how to use Commons Digester to parse XML data and convert it to Java objects.
import org.apache.commons.digester3.Digester;
public class Main {
public static void main(String[] args) {
// Create a DIGESTER instance
Digester digester = new Digester();
// Configuration rules collection
// Create Person objects and set attributes
digester.addObjectCreate("people/person", Person.class);
digester.addSetProperties("people/person");
// Set the value of the name element to the name property of the Person object
digester.addBeanPropertySetter("people/person/name", "name");
// Set the value of the AGE element to the AGE property of the Person object
digester.addBeanPropertySetter("people/person/age", "age");
// Analyze XML data
try {
Person person = digester.parse(new File("data.xml"));
System.out.println(person);
} catch (Exception e) {
e.printStackTrace();
}
}
}
class Person {
private String name;
private int age;
// omit the creation function and getter/setter method
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
}
In the above example, we use Digester to create a Person object, resolve the value of the name and Age property from the XML file, and finally output to the console.
Summarize:
Commons Digester is a powerful and flexible tool that can be used to process XML data and convert it into Java objects.Through DIGESTER, developers can easily handle XML, thereby simplifying the development process of Java applications.Whether it is configuration file analysis, web application development or test data generation, Digester is a tool worth using.
