In -depth analysis of the technical principles of Apache Commons Digest
Apache Commons Digester is a Java framework for processing XML files.It analyzes the XML file and maps the XML data into the Java object to simplify the processing process of the XML file.This article will deeply analyze the technical principles of the Apache Commons Digester framework and provide relevant Java code examples.
1. Digester framework overview
Apache Commons Digester is an open source Java library that is mainly used to map the XML data and Java objects.It provides a simple and flexible way to analyze the XML file by defining rules and processors, and automatically convert XML data into Java objects.
The main components in the DIGESTER framework are as follows:
1. DIGESTER object: The DIGESTER object is the core of the entire framework. It is responsible for analyzing XML files and transforming XML data into Java objects based on predetermined rules.
2. Rules: The rules define how to analyze the XML file and how to mappate XML data to the Java object.The DIGESTER framework provides some built -in rules, such as CallMethodrule, ObjectCreaterule, etc., and users can customize rules.
3. The processor (including object creation processor, attribute setting processor, method call processor, etc.): The processor defines specific operations to analyze XML data and map it to the Java object.
Second, the working principle of the DIGESTER framework
The working principle of the DIGESTER framework is as follows:
1. Create the DIGESTER object.First, a DIGESTER object needs to be created to analyze XML files.
Digester digester = new Digester();
2. Configure the DIGESTER object.Next, you need to configure the rules of the DIGESTER object.You can use built -in rules or custom rules.
digester.addRule("catalog/book", new ObjectCreateRule(Book.class));
digester.addRule("catalog/book", new SetPropertiesRule());
digester.addRule("catalog/book", new SetNextRule("addBook"));
In the above code, first use the adDRule () method to define when encountering the "Catalog/Book" node, you should use ObjectCreterule to create a Book object; then use SetpropertiesRule to set the attributes of the Book object; finally use the Setnextrule to pass the Book object to the adDBO. OK methodEssence
3. Analyze the XML file.Use the PARSE () method of the DIGESTER object to analyze the xml file.
Catalog catalog = (Catalog) digester.parse(xmlFile);
In the above code, the PARSE () method parses the XML file as a Java object and returns the analytical object.
Third, sample code
Below is a sample code that uses Apache Commons Digester framework to analyze XML files:
1. Define the XML file (Books.xml) to be parsed:
<catalog>
<book>
<title>Harry Potter</title>
<author>J. K. Rowling</author>
</book>
<book>
<title>The Great Gatsby</title>
<author>F. Scott Fitzgerald</author>
</book>
</catalog>
2. Define the Java object (Book.java):
public class Book {
private String title;
private String author;
// omit the getter and setter method
}
3. Create an analytical rule (catalogram .java):
public class CatalogRule extends RuleSetBase {
@Override
public void addRuleInstances(Digester digester) {
digester.addObjectCreate("catalog/book", Book.class);
digester.addSetProperties("catalog/book");
digester.addSetNext("catalog/book", "addBook");
}
}
4. Create a parser and parse the xml file (main.java):
public class Main {
public static void main(String[] args) throws IOException, SAXException {
Digester digester = new Digester();
digester.addRuleSet(new CatalogRule());
Catalog catalog = (Catalog) digester.parse(new File("books.xml"));
// Print the Resolution Result
for (Book book : catalog.getBooks()) {
System.out.println("Title: " + book.getTitle());
System.out.println("Author: " + book.getAuthor());
System.out.println();
}
}
}
In the above code, first created the DIGESTER object and added the CataLogrule rule set; then the PARSE () method parsed the XML file and stored the analytical results in the CATALOG object; the analysis result was finally output.
Summarize
This article analyzes the technical principles of the Apache Commons Digester framework, and provides an example of use.By using the DIGESTER framework, the processing process of the XML file can be simplified, and the mapping of XML data to the Java object can be achieved.It is hoped that this article can provide readers to understand the DIGESTER framework to provide some help to make it better applied to actual projects.
