Extending a basic web crawler to filter status codes and HTML

问题

I followed a tutorial on writing a basic web crawler in Java and have got something with basic functionality.

At the moment it just retrieves the HTML from the site and prints it to the console. I was hoping to extend it so it can filter out specifics like the HTML page title and the HTTP status code?

I found this library: http://htmlparser.sourceforge.net/ ... which I think might be able to do the job for me but could I do it without using an external library?

Here's what I have so far:

public static void main(String[] args) {

    // String representing the URL
    String input = "";

    // Check if argument added at command line
    if (args.length >= 1) {
        input = args[0];
    }

    // If no argument at command line use default
    else {
        input = "http://www.my_site.com/";
        System.out.println("\nNo argument entered so default of " + input
                + " used: \n");
    }
    // input test URL and read from file input stream
    try {

        testURL = new URL(input);
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                testURL.openStream()));

        // String variable to hold the returned content
        String line = "";

        // print content to console until no new lines of content
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
    } catch (Exception e) {

        e.printStackTrace();
        System.out.println("Exception thrown");
    }
}

回答1:

There are definitely tools out there for HTTP communication. However, if you prefer to implement one yourself - look into java.net.HttpURLConnection. It will give you more fine grained control over HTTP communications. Here's a little sample for you:

public static void main(String[] args) throws IOException
{
  URL url = new URL("http://www.google.com");
  HttpURLConnection connection = (HttpURLConnection) url.openConnection();

  connection.setRequestMethod("GET");

  String resp = getResponseBody(connection);

  System.out.println("RESPONSE CODE: " + connection.getResponseCode());
  System.out.println(resp);
}

private static String getResponseBody(HttpURLConnection connection)
    throws IOException
{
  try
  {
    BufferedReader reader = new BufferedReader(new InputStreamReader(
        connection.getInputStream()));

    StringBuilder responseBody = new StringBuilder();
    String line = "";

    while ((line = reader.readLine()) != null)
    {
      responseBody.append(line + "\n");
    }

    reader.close();
    return responseBody.toString();
  }
  catch (IOException e)
  {
    e.printStackTrace();
    return "";
  }
}

来源：https://stackoverflow.com/questions/11477341/extending-a-basic-web-crawler-to-filter-status-codes-and-html