Detailed explanation of the technical principles of the Apache Commons Digest frame in the Java class library
Apache Commons Digestter is a Java class library that is used to convert XML documents into Java objects.It uses an analysis mechanism called "parser to convert XML to the rule of Java objects". This rule is defined by a series of rules.
The core component of the DIGESTER is a parser that resolves the input XML document and generates the corresponding Java object according to the rules.The parser is based on an event -driven model. When it encounters a specific event in the XML document, the corresponding rules are called.
The rules are defined through a series of methods. These methods tell Digester what operations should be performed when encountering specific XML elements.For example, a rule defines when the parser encounters an XML element called "Person", create a Person object and set the data in the XML element.
Here are a simple example of using Digest:
import org.apache.commons.digester3.Digester;
public class Example {
private static class Person {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
}
public static void main(String[] args) throws Exception {
Digester digester = new Digester();
digester.setValidating(false);
digester.addObjectCreate("person", Person.class);
digester.addBeanPropertySetter("person/name", "name");
digester.addBeanPropertySetter("person/age", "age");
digester.push(new ArrayList<Person>());
digester.addSetNext("person", "add");
String xml = "<persons>" +
"<person><name>Alice</name><age>25</age></person>" +
"<person><name>Bob</name><age>30</age></person>" +
"</persons>";
List<Person> persons = (List<Person>) digester.parse(new StringReader(xml));
for (Person person : persons) {
System.out.println(person);
}
}
}
In this example, we define a `Person` class, which has the` name` and `agter and setter methods.Then, we initialize the DIGESTER by creating a DIGESTER object and setting the `validating` property as false.
Next, we use the `addObjectCreate` method to tell Digetster to create an` Person` object when encountering XML element `person`.Then, we use the `adDBeanpropertySetter` method to tell Digest to set the value to the corresponding attribute when encountering the` Person/name` and `Person/Age` elements.
Finally, we push an empty `ArrayList <Person>` object into the object stack of Digester through the `push`In the list.
Finally, we pass the XML document containing the `Person` element as a string to the` Digester.parse` method, and print the returned `list <person> to the console.
To sum up, the Apache Commons Digester framework uses a series of rules to analyze XML documents and convert XML data to Java objects based on these rules.This makes processing XML data simple and flexible.
