HTTP and Java

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)

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

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

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

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

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”

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)

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

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

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(HttpExchange exchange)” method

• server.start()

HttpExchange Code• An HttpExchange encapsulates an HTTP request received and a response to be generated in one

exchange.• exchange.sendResponseHeaders(int rCode, 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());