NOTE: These slides have not been updated since 2003. They have been superseded by the book An Introduction to XML and Web Technologies Addison-Wesley, and the accompanying online material. Please see http://www.brics.dk/ixwt/ for more information. Anders Møller and Michael Schwartzbach, February 2006

INTERACTIVE WEB SERVICES WITH JAVA

The java.net Package

The most relevant classes and methods:

• URL
  • URL(String spec) - constructor
  • URLConnection openConnection() - creates TCP connection of type given by the protocol

• URLConnection (interface) / HttpURLConnection (subclass) - for making HTTP requests
  • void setRequestMethod(String method) - set method (GET/POST/... - default is GET)
  • void setDoOutput(boolean dooutput) - intend to use connection for output
  • void setDoInput(boolean doinput) - intend to use connection for input
  • OutputStream getOutputStream() - output stream
  • InputStream getInputStream() - input stream
  • void setRequestProperty(String key, String value) - set request header
  • Hashtable getHeaderFields() - read response header
  • Object getContent() - read input and convert to an object
  • ...

• URLEncoder / URLDecoder - for encoding/decoding special chars in URLs (application/x-www-form-urlencoded)
  • String encode(String s)
  • String decode(String s)

Example:

import java.net.*; import java.io.*; public class AltaVista { public static void main (String args[]) { try { // make connection URL url = new URL("http://www.altavista.com/cgi-bin/query?q=" + URLEncoder.encode(args[0])); URLConnection connection = url.openConnection(); connection.setDoInput(true); InputStream in = connection.getInputStream(); // read reply StringBuffer b = new StringBuffer(); BufferedReader r = new BufferedReader(new InputStreamReader(in)); String line; while ((line = r.readLine()) != null) b.append(line); String s = b.toString(); // look for first search result, if any if (s.indexOf(">We found 0 results") != -1) System.out.println("No results found."); else { int i = s.indexOf("\"status='")+9; int j = s.indexOf("'", i); System.out.println("First result: " + s.substring(i, j)); } } catch (Exception e) { e.printStackTrace(); } } }

(sends a query to the AltaVista search engine and extracts the first result)

Other useful classes in java.net:

• InetAddress - IP addresses (DNS lookup, etc.)
• Socket,ServerSocket - TCP sockets (as in example client and server)
• ProtocolHandler - defines mapping for URL.openConnection() to concrete URLConnection
• ContentHandler - defines mapping for getObject() to Object (based on MIME type)

• Applets: java.applet
• Remote Method Invocation: java.rmi
• XML (JDOM, JAXP)

COPYRIGHT © 2002-2003 ANDERS MØLLER & MICHAEL I. SCHWARTZBACH