Understanding HTTP and Java Communication Protocols

1. HTTP and Java

2. Background • TCP/IP • Break message into packets • Give each packet a number and total number of packets in message • Destination IP address and port numbers • Source IP address and port • IP Address (v4 and v6) • Port Number (0 to 216-1) • Well Know (0-1023) • Registered (1024-49151) • Dynamic, private, ephemeral (all the rest)

3. Sockets • Internet Sockets • Listener or Server Socket • Client Sockets • Two way connection provides two way communication • Operating specific means of • Opening • Closing • Transmitting to and from a “socket” • Often uses a protocol like TCP/IP • In Java it is viewed as a stream

4. Hypertext Transfer Protocol • Application level • Provides communication between applications • Usually a client and server (though it may be peer-to-peer) • Underlying transport layer is TCP/IP • Request-Response Protocol • Used for sending and receiving various types of information • Used in web-applications especially in HTML-based applications

5. High-level View • An HTTP Session • Client establishes a TCP connection to a particular port (e.g. port 80) • Server waits for message from Client • Upon receipt the server sends back a • Status (e.g. ok) • Response • Requested Information • Error Message • Or it could be empty

6. Message Types:HTTP Request • Request Line • GET or POST with pathToResource • Header Lines • Header Name – Value Pairs • Example Names: From:, User-Agent: • Blank Line • Optional Message Body • Gets don’t have a Message Body • For example: XML Encoded information in a POST

7. Message TypesHTTP Response • Status Line • For example: • HTTP/1.0 200 OK • HTTP/1.0 404 Not Found • Header Lines • Header Name – Value Pairs • Example Names: Server:, Last-Modified: • Blank Line • Optional Message Body • Examples • HTML • XML Encoded Information is a response expected • Could be blank for a pure “POST”

8. Request Methods • GET • Should be used to retrieve information, not modify information on the server • Not enforced and some gets don’t conform to this suggestion, can cause problems • Encodes parameters in URL sent to server • Appears in the request line (the first line) • Server may have URL length limits (e.g. 2083 characters)

9. Request Methods • POST • Should be used to change information • Information sent in message body • Can be any format (including binary) • We will use XML • Is of arbitrary size

10. HTTP And Java • Several “HTTP” servers written in Java • Jetty • Apache • Oracle HTTPServer • Built into Oracle’s Java 1.6 and 1.7 • Import com.sun.net.httpserver.*; • We will use this one

11. HttpServer Code • HttpServer server; • HTTPServer.create( new InetSocketAddress(portNumber), maxNumberOfConnections); • server.setExecutor(null); • Default thread pool manager • server.createContext(URLSuffix, handlerMethodObject) • Handler for various suffixes in the URL • Handler “method” is a Command object that extends HttpHandler • HttpHandler has one method: void handle(HttpExchange exchange) • Often the handler is declared as an instance of an anonymous inner type that overrides the “void handle(HttpExchangeexchange)” method • server.start()

12. HttpExchange Code • An HttpExchangeencapsulates an HTTP request received and a response to be generated in one exchange. • exchange.sendResponseHeaders(intrCode, responseLength) • rCode is often a constant found in HttpURLConnection • Examples • HttpURLConnection.HTTP_INTERNAL_ERROR • HttpURLConnection.HTTP_OK, • responseLength • 0 means an arbitrary size • -1 means no response body • exchange.getRequestBody(); • Gets the body of the request as an input stream • Used as a parameter to xmlStream.fromXML(exchange.getRequestBody()); • exchange.getResponseBody(); • Gets the body of the request as an input stream • Used as a parameter to xmlStream.toXML(object, exchange.getResponseBody());