The design of the design of the HTML2SAX framework and the application of the technical principle in the Java class library
The design and technical principle of the HTML2SAX framework in the Java library
Summary:
HTML2SAX is a framework that analyzes HTML documents as SAX (Simple API for XML) event model.This article will explore the design principles and technical principles of the HTML2SAX framework and introduce its application in the Java class library.At the same time, we will also provide some Java code examples to help readers better understand how to use the HTML2SAX framework.
1 Introduction
In many practical applications, we need to analyze and handle HTML documents.The commonly used HTML parsing library such as JSOUP or HTMLPARSER provides DOM (document object model) to resolve HTML, but they usually load the entire HTML document to the memory, which will bring great memory pressure when dealing with large HTML documents.In contrast, the HTML2SAX framework uses the SAX event model, which can read and handle HTML in the process of parsing to avoid the problem of memory occupation.
2. Design principle
The design idea of the HTML2SAX framework is to convert the HTML document into the SAX event stream and trigger the corresponding event processing program.The SAX event model is provided by the XML parser, and the different parts of the documentation are handled by calling the callback method of the parser.On the basis of this, HTML2SAX expands it, resolves the HTML mark into SAX events, and provides a set of custom event processor interfaces so that users can handle various HTML elements according to their needs.
3. Technical principles
The core of the HTML2SAX framework is a HTML parser, which is responsible for converting the HTML document into the SAX event flow.The parser uses the design mode of a state machine, reads the HTML document by word, and updates the status according to the current state and input characters.When the parser encounters the HTML mark, it triggers the corresponding event according to the type of the tag and calls the registered event processor.
The HTML2SAX framework also provides a default event processor to handle common HTML elements, such as title, paragraphs, links, images, etc.Users can also implement their own event processor as needed and register into the parser.In this way, when the parser is parsed to the corresponding HTML element, the corresponding event processor will be called to handle the element.
4. Application in the Java library
It is very simple to use the HTML2SAX framework in the Java library.First, we need to import the HTML2SAAAAAAAAAA class library.Then create a parser object and pass into the HTML document to be parsed.Finally, the registered event processor began to analyze.The following is a simple example:
import com.example.html2sax.HtmlParser;
import com.example.html2sax.EventHandler;
import com.example.html2sax.DefaultEventHandler;
public class Main {
public static void main(String[] args) {
String html = "<html><body><h1>Hello, World!</h1></body></html>";
HtmlParser parser = new HtmlParser();
EventHandler eventHandler = new DefaultEventHandler();
parser.registerEventHandler(eventHandler);
parser.parse(html);
}
}
In the above example, we first created an HTMLPARSER object, and then instantly chemotized a defaultEventhandler object as an event processor and registered it into the parser.Finally, we call the `Parse` method to start parsing HTML documents.When the parser is parsed to the `h1>` mark, the corresponding method defined in the defaultEventhandler is called to handle the mark.
By expanding the DefaultEventhandler class, we can customize the event processor and implement our own event processing logic.This makes the HTML2SAX framework very flexible and can be expanded and customized according to actual needs.
5 Conclusion
The HTML2SAX framework is an effective tool for analyzing and processing HTML documents in the Java class library.By using HTML2SAX, we can avoid loading the problems from the entire HTML document to the memory, and to deal with HTML one by one to improve the efficiency of analysis.At the same time, the HTML2SAX framework also provides a flexible event processing mechanism, allowing users to process different types of HTML elements according to their own needs.
It is hoped that through this article, the design principles and technical principles of the HTML2SAX framework can be used flexibly in actual development.
