Use javax.swing.text.html.HTMLEditorKit to parse HTML : HTML Parser « Development « Java Tutorial

1. Java Tutorial
2. Development
3. HTML Parser

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.net.URL;

import javax.swing.text.MutableAttributeSet;
import javax.swing.text.html.HTML;
import javax.swing.text.html.HTMLEditorKit;

public class MainClass {
  private static void parse(URL url, String encoding) throws IOException {
    ParserGetter kit = new ParserGetter();
    HTMLEditorKit.Parser parser = kit.getParser();
    InputStream in = url.openStream();
    InputStreamReader r = new InputStreamReader(in, encoding);
    HTMLEditorKit.ParserCallback callback = new Outliner(new OutputStreamWriter(System.out));
    parser.parse(r, callback, true);
  }

  public static void main(String[] args) throws Exception {

    ParserGetter kit = new ParserGetter();
    HTMLEditorKit.Parser parser = kit.getParser();

    String encoding = "ISO-8859-1";
    URL url = new URL("http://www.java2s.com");
    InputStream in = url.openStream();
    InputStreamReader r = new InputStreamReader(in, encoding);
    // parse once just to detect the encoding
    HTMLEditorKit.ParserCallback doNothing = new HTMLEditorKit.ParserCallback();
    parser.parse(r, doNothing, false);

    parse(url, encoding);
  }

}

class Outliner extends HTMLEditorKit.ParserCallback {

  private Writer out;

  private int level = 0;

  private boolean inHeader = false;

  private static String lineSeparator = System.getProperty("line.separator", "\r\n");

  public Outliner(Writer out) {
    this.out = out;
  }

  public void handleStartTag(HTML.Tag tag, MutableAttributeSet attributes, int position) {

    int newLevel = 0;
    if (tag == HTML.Tag.H1)
      newLevel = 1;
    else if (tag == HTML.Tag.H2)
      newLevel = 2;
    else if (tag == HTML.Tag.H3)
      newLevel = 3;
    else if (tag == HTML.Tag.H4)
      newLevel = 4;
    else if (tag == HTML.Tag.H5)
      newLevel = 5;
    else if (tag == HTML.Tag.H6)
      newLevel = 6;
    else
      return;

    this.inHeader = true;
    try {
      if (newLevel > this.level) {
        for (int i = 0; i < newLevel - this.level; i++) {
          out.write("<ul>" + lineSeparator + "<li>");
        }
      } else if (newLevel < this.level) {
        for (int i = 0; i < this.level - newLevel; i++) {
          out.write(lineSeparator + "</ul>" + lineSeparator);
        }
        out.write(lineSeparator + "<li>");
      } else {
        out.write(lineSeparator + "<li>");
      }
      this.level = newLevel;
      out.flush();
    } catch (IOException ex) {
      System.err.println(ex);
    }

  }

  public void handleEndTag(HTML.Tag tag, int position) {

    if (tag == HTML.Tag.H1 || tag == HTML.Tag.H2 || tag == HTML.Tag.H3 || tag == HTML.Tag.H4
        || tag == HTML.Tag.H5 || tag == HTML.Tag.H6) {
      inHeader = false;
    }

    // work around bug in the parser that fails to call flush
    if (tag == HTML.Tag.HTML)
      this.flush();

  }

  public void handleText(char[] text, int position) {

    if (inHeader) {
      try {
        out.write(text);
        out.flush();
      } catch (IOException ex) {
        System.err.println(ex);
      }
    }

  }

  public void flush() {
    try {
      while (this.level-- > 0) {
        out.write(lineSeparator + "</ul>");
      }
      out.flush();
    } catch (IOException e) {
      System.err.println(e);
    }
  }

  private static void parse(URL url, String encoding) throws IOException {
    ParserGetter kit = new ParserGetter();
    HTMLEditorKit.Parser parser = kit.getParser();
    InputStream in = url.openStream();
    InputStreamReader r = new InputStreamReader(in, encoding);
    HTMLEditorKit.ParserCallback callback = new Outliner(new OutputStreamWriter(System.out));
    parser.parse(r, callback, true);
  }

}

class ParserGetter extends HTMLEditorKit {
  public HTMLEditorKit.Parser getParser() {
    return super.getParser();
  }
}