How do you Programmatically Download a Webpage in Java

Question

I'd use a decent HTML parser like Jsoup. It's then as easy as:

String html = Jsoup.connect("http://stackoverflow.com").get().html();

It handles GZIP and chunked responses and character encoding fully transparently. It offers more advantages as well, like HTML traversing and manipulation by CSS selectors like as jQuery can do. You only have to grab it as Document, not as a String.

Document document = Jsoup.connect("http://google.com").get();

You really don't want to run basic String methods or even regex on HTML to process it.

See also:

• What are the pros and cons of leading HTML parsers in Java?

Here's some tested code using Java's URL class. I'd recommend do a better job than I do here of handling the exceptions or passing them up the call stack, though.

public static void main(String[] args) {
    URL url;
    InputStream is = null;
    BufferedReader br;
    String line;

    try {
        url = new URL("http://stackoverflow.com/");
        is = url.openStream();  // throws an IOException
        br = new BufferedReader(new InputStreamReader(is));

        while ((line = br.readLine()) != null) {
            System.out.println(line);
        }
    } catch (MalformedURLException mue) {
         mue.printStackTrace();
    } catch (IOException ioe) {
         ioe.printStackTrace();
    } finally {
        try {
            if (is != null) is.close();
        } catch (IOException ioe) {
            // nothing to see here
        }
    }
}

Bill's answer is very good, but you may want to do some things with the request like compression or user-agents. The following code shows how you can various types of compression to your requests.

URL url = new URL(urlStr);
HttpURLConnection conn = (HttpURLConnection) url.openConnection(); // Cast shouldn't fail
HttpURLConnection.setFollowRedirects(true);
// allow both GZip and Deflate (ZLib) encodings
conn.setRequestProperty("Accept-Encoding", "gzip, deflate");
String encoding = conn.getContentEncoding();
InputStream inStr = null;

// create the appropriate stream wrapper based on
// the encoding type
if (encoding != null && encoding.equalsIgnoreCase("gzip")) {
    inStr = new GZIPInputStream(conn.getInputStream());
} else if (encoding != null && encoding.equalsIgnoreCase("deflate")) {
    inStr = new InflaterInputStream(conn.getInputStream(),
      new Inflater(true));
} else {
    inStr = conn.getInputStream();
}

To also set the user-agent add the following code:

conn.setRequestProperty ( "User-agent", "my agent name");

Well, you could go with the built-in libraries such as URL and URLConnection, but they don't give very much control.

Personally I'd go with the Apache HTTPClient library.
Edit: HTTPClient has been set to end of life by Apache. The replacement is: HTTP Components

All the above mentioned approaches do not download the web page text as it looks in the browser. these days a lot of data is loaded into browsers through scripts in html pages. none of above mentioned techniques supports scripts, they just downloads the html text only. HTMLUNIT supports the javascripts. so if you are looking to download the web page text as it looks in the browser then you should use HTMLUNIT.

You'd most likely need to extract code from a secure web page (https protocol). In the following example, the html file is being saved into c:\temp\filename.html Enjoy!

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;

import javax.net.ssl.HttpsURLConnection;

/**
 * <b>Get the Html source from the secure url </b>
 */
public class HttpsClientUtil {
    public static void main(String[] args) throws Exception {
        String httpsURL = "https://stackoverflow.com";
        String FILENAME = "c:\\temp\\filename.html";
        BufferedWriter bw = new BufferedWriter(new FileWriter(FILENAME));
        URL myurl = new URL(httpsURL);
        HttpsURLConnection con = (HttpsURLConnection) myurl.openConnection();
        con.setRequestProperty ( "User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:63.0) Gecko/20100101 Firefox/63.0" );
        InputStream ins = con.getInputStream();
        InputStreamReader isr = new InputStreamReader(ins, "Windows-1252");
        BufferedReader in = new BufferedReader(isr);
        String inputLine;

        // Write each line into the file
        while ((inputLine = in.readLine()) != null) {
            System.out.println(inputLine);
            bw.write(inputLine);
        }
        in.close(); 
        bw.close();
    }
}

To do so using NIO.2 powerful Files.copy(InputStream in, Path target):

URL url = new URL( "http://download.me/" );
Files.copy( url.openStream(), Paths.get("downloaded.html" ) );