Master the technical core of the "HTML PARSER" framework in the Java library
Master the technical core of the "HTML PARSER" framework in the Java library
Overview:
HTML Parser is an open source framework for analyzing HTML documents in Java.It provides a simple and efficient way to analyze, traverse, and operate HTML documents so that developers can easily extract the required content.This article will introduce the technical core of the HTML Parser framework and provide some Java code examples to help readers better understand and use the framework.
1. Introduce the HTML Parser framework
To use the HTML Parser framework, you need to introduce it into the project first.The introduction can be completed by adding dependencies in the construction file of the project, or the introduction of the JAR file into the project of the project directly.The following is an example when using Maven to build a project, adding HTML PARSER dependencies to the POM.XML file:
<dependency>
<groupId>nu.validator.htmlparser</groupId>
<artifactId>htmlparser</artifactId>
<version>1.7.0</version>
</dependency>
2. Analyze the HTML documentation
It is very simple to use the HTML Parser framework to analyze the HTML document.The following is an example that demonstrates how to analyze an HTML file and get the title and all links:
import org.htmlparser.Node;
import org.htmlparser.Parser;
import org.htmlparser.filters.HasAttributeFilter;
import org.htmlparser.tags.LinkTag;
import org.htmlparser.util.ParserException;
public class HTMLParserExample {
public static void main(String[] args) {
try {
// Create HTML Parser instance
Parser parser = new Parser("http://example.com");
// Get all title nodes
Node[] titleNodes = parser.extractAllNodesThatMatch(node -> node.getText().startsWith("h"));
// Print title text
for (Node node : titleNodes) {
System.out.println(node.toPlainTextString());
}
// Get all link nodes
Node[] linkNodes = parser.extractAllNodesThatMatch(new HasAttributeFilter("href"));
// Print link text and URL
for (Node node : linkNodes) {
if (node instanceof LinkTag) {
LinkTag linkTag = (LinkTag) node;
System.out.println(linkTag.getLinkText() + ": " + linkTag.getLink());
}
}
} catch (ParserException e) {
e.printStackTrace();
}
}
}
The above example first creates a Parser instance and specifies the URL of the HTML document to be parsed.Then, use the ExtractallNodeSthatmatch method and custom conditional filter to obtain title nodes and link nodes.Finally, the text and url of the print node.
3. Operation HTML document
The HTML Parser framework also provides some advanced functions to operate HTML documents more conveniently.The following is an example that demonstrates how to find specific elements in the HTML document and modify its attributes:
import org.htmlparser.Node;
import org.htmlparser.Parser;
import org.htmlparser.filters.HasAttributeFilter;
import org.htmlparser.nodes.TagNode;
import org.htmlparser.tags.ImageTag;
import org.htmlparser.util.NodeList;
import org.htmlparser.util.ParserException;
import org.htmlparser.visitors.NodeVisitor;
public class HTMLManipulationExample {
public static void main(String[] args) {
try {
// Create HTML Parser instance
Parser parser = new Parser("http://example.com");
// Get all picture nodes
NodeList imageNodes = parser.extractAllNodesThatMatch(new HasAttributeFilter("src", ".+\\.jpg"));
// Modify the width attribute of all picture nodes
imageNodes.visitAllNodesWith(new NodeVisitor() {
@Override
public void visitTag(TagNode tagNode) {
if (tagNode instanceof ImageTag) {
ImageTag imageTag = (ImageTag) tagNode;
imageTag.setAttribute("width", "200");
}
}
});
// Print the modified html document
System.out.println(parser.getHTML());
} catch (ParserException e) {
e.printStackTrace();
}
}
}
The above example first obtains all the picture nodes, and its src attribute ended with ".jpg".Then, through the visitor (VISITOR) mode, you traverse all the picture nodes and modify the width attribute.Finally, print the modified HTML document.
in conclusion:
By mastering the technical core of the HTML Parser framework in the Java library, we can easily analyze, traverse and operate HTML documents.This article provides a method to introduce the HTML Parser framework and gives a sample code for analysis and operation of HTML documents. It is hoped that readers will help readers with certain help in actual projects.
