The technical principles of the "HTML PARSER" framework in the Java class library
"HTML PARSER" framework technical principles in the Java class library
Introduction:
HTML Parser is a Java class library for parsing HTML documents. It provides many powerful tools that enable developers to easily extract the required information from the HTML document.This article will conduct in -depth exploration of the technical principles of the HTML Parser framework and demonstrate its use method through the Java code example.
1. The basic principle of the HTML Parser framework
The basic principle of HTML Parser is to analyze the label and content of the HTML document, and convert it to the Java object to facilitate developers to operate and handle HTML documents.The HTML Parser framework mainly includes the following core components:
1. parser (Parser): The parser is the core component of HTML Parser, which is responsible for converting HTML documents into Java objects.The parser constructs the tree -shaped data structure that indicates the HTML document structure by scanning the label and content of the HTML document.
2. Node (Node): Node is the basic data structure in the HTML Parser framework, indicating the labels, attributes and text content in the HTML document.Nodes are similar to nodes in the tree. Each node contains information such as label names, attribute lists, and sub -nodes. Developers can obtain, modify and delete the content in HTML documents by operating nodes.
3. Nodeiterator: The traverser is a tool used in the traversal tree tree in the HTML Parser framework. Developers can use the traverser to access and operate the nodes in the HTML document.The traverser provides a series of methods, such as obtaining the current node, moving to the next or the previous node.
4. NodeFilter: The filter is a tool for screening and filter nodes in the HTML Parser framework. Developers can use filters to select nodes that meet specific conditions.The filter can screen the nodes through the name, attribute or path of the node.
Example of the use of the HTML Parser framework
The following is a simple example to demonstrate how to use the HTML Parser framework to analyze and process HTML documents:
import org.htmlparser.Node;
import org.htmlparser.Parser;
import org.htmlparser.filters.TagNameFilter;
import org.htmlparser.util.NodeList;
public class HtmlParserExample {
public static void main(String[] args) {
try {
// Create a parser and specify the html document URL
Parser parser = new Parser("http://example.com");
// Use a parser to parse the HTML document
NodeList nodeList = parser.parse(new TagNameFilter("a"));
// Traversing the list of nodes and output node text content
for (Node node : nodeList.toNodeArray()) {
System.out.println(node.toPlainTextString());
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
In the above example, we first created a parser object, and then resolved HTML by specifying the URL of the HTML document.Next, we use the filter to select all the `<a>` tag nodes and store the results in a node list.Finally, we traversed this node list and output the pure text content of the node.
3. Summary
The HTML Parser framework is a powerful Java class library that provides convenient methods to analyze and handle HTML documents.By using HTML Parser, developers can easily extract the required information from the HTML document and operate and processes the HTML document.
