Java Network Programming, Second Edition

Reading Data from a Server

The minimal set of steps needed to retrieve data from a URL using a URLConnection object are these:

1. Construct a URL object.

2. Invoke the URL object’s openConnection( ) method to retrieve a URLConnection object for that URL.

3. Invoke the URLConnection’s getInputStream( ) method.

4. Read from the input stream using the usual stream API.

The getInputStream( ) method returns a generic InputStream, which lets you read and parse the data that the server sends yourself.

public InputStream getInputStream(  )

Example 15.1 uses the getInputStream( ) method to download a web page.

Example 15-1. Download a Web Page with a URLConnection

import java.net.*;
import java.io.*;

public class SourceViewer2 {

  public static void main (String[] args) {

    if  (args.length > 0) {
      try {
        //Open the URLConnection for reading
        URL u = new URL(args[0]);
        URLConnection uc = u.openConnection(  );
        InputStream raw = uc.getInputStream(  );
        InputStream buffer = new BufferedInputStream(raw);       
        // chain the InputStream to a Reader
        Reader r = new InputStreamReader(buffer);
        int c;
        while ((c = r.read(  )) != -1) {
          System.out.print((char) c);
        } 
      }
      catch (MalformedURLException e) {
        System.err.println(args[0] + " is not a parseable URL");
      }
      catch (IOException e) {
        System.err.println(e);
      }

    } //  end if

  } // end main

}  // end SourceViewer2

It is no accident that this program is almost the same as Example 15.5. The openStream( ) method of the URL class just returns an InputStream from its own URLConnection object. The output ...