Use the HTML parser framework in the Java Library to analyze the principles and practice of the webpage
Use the HTML parser framework in the Java Library to analyze the principles and practice of the webpage
introduction:
In today's information age, web pages have become one of the main channels for people to obtain various information.However, the content of the webpage is often presented in the form of HTML, and HTML is not designed for machine analysis.Therefore, in order to extract and analyze the key information in the webpage, we need to use HTML parser to resolve the structured data of the webpage.The Java class library provides many powerful HTML parser frameworks. This article will introduce its working principles and share actual experience.
1. The working principle of the HTML parser framework:
The HTML parser framework reads the character stream in the HTML document and analyzes and analyzes the document structure according to the rules of the HTML mark. In the end, a document tree (DOM) that can operate and extract information can be generated.It converts the HTML document into a node tree organized by hierarchical relations to facilitate developers to extract and analyze web content by traversing and operating nodes.
HTML parser framework usually includes the following main components and workflows:
1. HTML document load: The parser will first load the HTML document to be parsed, which can be a local file or a URL link on a network.
2. Character flow reading: The parser will read the character flow in the HTML document according to the document loading method.
3. Ci -method analysis: The parser analyzes the phrases of character flow, and separates and recognizes the text content between the HTML markers and the mark.
4. Grammar analysis: The parser will analyze and build a document tree node one by one according to the grammatical rules of HTML.
5. Generate a DOM tree: The parser through the hierarchical relationship of the node, organize the analysis of the node obtained according to the tree structure to form the so -called DOM tree.
6. Node traversing and operation: Developers can use the nodes of the DOM tree to extract and operate the content according to need.
Second, the practice of HTML parser framework:
Below we use a practical example to demonstrate how to use the HTML parser framework in the Java class library to analyze the webpage.
We first need to introduce a commonly used HTML parser framework, such as JSOUP.You can add it to the project through Maven and other dependent management tools.
Example code:
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;
public class HtmlParserExample {
public static void main(String[] args) {
try {
// 1. Load HTML documentation
Document document = Jsoup.connect("http://example.com").get();
// 2. Get the page title
String title = document.title();
System.out.println ("page title:" + Title);
// 3. Get all links
Elements links = document.select("a[href]");
for (Element link : links) {
System.out.println ("Link:" + Link.attr ("href");
}
// 4. Get specific element content
Element element = document.selectFirst("p");
System.out.println ("Paragraph Content:" + Element.text ());
} catch (Exception e) {
e.printStackTrace();
}
}
}
In the above example code, we loaded a web example (http://example.com) through the JSOUP framework, and extracted the title, link and paragraph content by calling the API provided by JSOUP.You can also use other APIs to extract and operate other content on the web according to your needs.
3. Summary:
Using the HTML parser framework in the Java class library can help us easily analyze the structured data of the webpage and extract key information in it.This article introduces the working principle of the HTML parser framework, and shows how to use the JSOUP framework to analyze and operate the content of the webpage through the example code.Mastering and flexibly using the HTML parser framework will bring great convenience to our web crawlers, information extraction and data analysis.
