Explore the working principle of the HTML parser JAR framework in the Java class library

HTML parser is a tool for parsing HTML documents. It can analyze HTML documents into structured data, which is convenient for the program to process and analyze the HTML document.In the Java class library, there are many excellent HTML parser JAR frameworks, such as JSOUP, HTMLPARSER, etc. They all use different parsing algorithms and APIs, but their working principles are generally the same. The working principle of the html parser is as follows: 1. First of all, the HTML parser needs to load the HTML document to the memory. You can obtain the HTML source code through network requests and file reading, and save it in a string or input stream. 2. Then, the HTML parser will analyze the HTML source code by character in accordance with the grammatical rules marked by HTML.During the analysis process, the parser will generate the corresponding data structure according to the label type, such as labels, attributes, text content, etc. to represent the structure and content of the HTML document.Generally, the parser uses some data structures, such as trees, nodes, etc. to indicate the structure of the HTML document. 3. In the process of parsing, the HTML parser will identify various HTML marks and adopt corresponding processing logic according to the different types of mark type.For example, for the HTML label, the parser will analyze its label name, attributes, sub -nodes and other information, and build it into the corresponding data structure.For text content, the parser will save it in a specific data structure. 4. During the parsing process, the HTML parser will also handle some special circumstances, such as automatic correction of HTML syntax errors, handling nested labels, and rotating characters.The parser will convert the HTML document as much as possible into the correct structured data so that the program can accurately process these data. 5. Finally, the HTML parser will return the data structure obtained by the parsing to the caller, and the caller can obtain and operate these structured data through the API.Generally, the parser provides some commonly used APIs, such as the content of the specific label, traversing document tree, etc., so as to facilitate the program to further process and analyze the HTML document. Take JSOUP as an example to give a simple Java code example to demonstrate how to use JSOUP to resolve HTML documents: import org.jsoup.Jsoup; import org.jsoup.nodes.Document; import org.jsoup.nodes.Element; import org.jsoup.select.Elements; import java.io.IOException; public class HtmlParserExample { public static void main(String[] args) { try { // Obtain HTML documents through the jsoup.connect method Document document = Jsoup.connect("https://example.com/").get(); // Get the page title String title = document.title(); System.out.println ("Title:" + Title); // Get the link of all A tags Elements links = document.select("a[href]"); for (Element link : links) { System.out.println ("Link:" + Link.attr ("href"); } } catch (IOException e) { e.printStackTrace(); } } } The above code uses the JSOUP framework to analyze a webpage and obtain the title of the page and the link of all A tags.First, obtain the Document object corresponding to the HTML document through the JSOUP.CONNECT method, and then obtain the required data through the method of the Document object. In summary, the working principle of the HTML parser JAR framework in the JAVA class library is to provide the API to make the API allow the program to easily process and analyze the HTML document by resolving the HTML document as a structured data.Among them, the parser will analyze the HTML document according to the grammatical rules marked by the HTML, and generate the corresponding data structure to represent the structure and content of the HTML document.By using the HTML parser, we can easily handle and analyze the HTML document in the Java program.