The technical principles and implementation of the HTML2SAX framework in the Java class library
The technical principles and implementation of the HTML2SAX framework in the Java class library
Overview
In Java development, we often need to handle HTML documents.HTML2SAX is a lightweight HTML parsing framework. It provides a parser model based on event -driven resolutions that convert HTML documents into SAX event streams.This article will introduce the technical principles and implementation of the HTML2SAX framework, as well as providing some Java code examples.
1. Technical principle
The core principle of the HTML2SAX framework is to analyze the HTML document into a series of SAX events, and use these events to handle it flexibly.The main implementation steps are as follows:
a. Use the SAX parser provided by Java, such as Xercess or WoodStox, and create a SAX parser object.
b. Implement a custom SAX event processing program (Contenthandler) to handle the SAX event stream.
c. Alert the SAX parser object to the custom event processing program to trigger the corresponding event processing method during the parsing process.
d. When the parser starts to resolve HTML documents, a series of SAX events will be triggered, such as starting documents, starting elements, character data, ending elements, etc.
e. In custom event processing procedures, handle these SAX events as needed, and extract the required data or perform other operations.
2. Framework implementation
Below is a simple Java code example, demonstrating how to use the HTML2SAX framework to parse the HTML document and extract the link in it.
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
public class HtmlParser extends DefaultHandler {
private List<String> links;
public void parseHtml(String url) {
try {
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
URL htmlUrl = new URL(url);
parser.parse(htmlUrl.openStream(), this);
} catch (ParserConfigurationException | SAXException | IOException e) {
e.printStackTrace();
}
}
@Override
public void startDocument() throws SAXException {
links = new ArrayList<>();
}
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
if (qName.equalsIgnoreCase("a")) {
String link = attributes.getValue("href");
if (link != null && !link.isEmpty()) {
links.add(link);
}
}
}
public List<String> getLinks() {
return links;
}
public static void main(String[] args) {
HtmlParser htmlParser = new HtmlParser();
htmlParser.parseHtml("https://example.com");
List<String> links = htmlParser.getLinks();
for (String link : links) {
System.out.println(link);
}
}
}
In the above code, we first define an HTMLPARSER class to inherit the DefaultHandler, which implements the SAX event processing program.In the Parsehtml method, we analyze the HTML document as the SAX event flow through the creation of the SaxParser parser object, and obtain the HTML document through the specified URL.
In the Startelement method, according to the starting element event of the <a> label, we extracted the HREF attribute value and added it to the Links list.
Finally, we create an HTMLPARSER instance in the main method and call the PARSEHTML method to resolve the given URL, and then obtain the extracted link and output.
Summarize
The HTML2SAX framework uses Java's SAX parser and custom event processing program to enable us to analyze and process HTML documents in an event -driven manner.By implementing custom event processing procedures, we can extract the data required or perform other operations according to specific needs.This event -based analysis model makes the HTML2SAX framework very efficient and flexible when processing large HTML documents.
