Http Java Networking

1
Http - Java Networking

• Lecture 12

2
Introduction to Networking Http server
Http server static pages (HTML)?
Http server dynamic pages (CGI)?
Http server dynamic pages (SSI)?
Http server dynamic pages (SSI/Servlets)?
Http server dynamic pages (Pure Java Servlets)?
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Introduction to Networking Http Server

• HTTP Server Static html pages
• Allowed only text and graphics (and yes, the
  annoying animated gifs)?
• Basically nothing more than a file server that
  displayed the html in a browser
• Really a standard format for document
  presentation
• Worked as a pure iterative server
• Anything that worked as a presentation layer
  display worked as html
• Embedded graphics, formatting, more than word
• Other standards such as Microsoft Word, Adobe
  PDF, RTF, LaTex, etc were binary representations,
  HTML is XML text and binary mime typed graphics

4
Introduction to Networking Http Server

• HTTP Server CGI need for dynamic pages
• Let other executables render the HTML pages
• CGI - common gateway interface allows any
  programming language.
• First iterations of CGI would allow only a
  program to be execed out of the web server
  process (dangerous)?
• GET / Post methods
• 2 ways to get data to a process
• GET uses a plain text variables passed in
  through the URL
• POST CGI process receives data via standard in
• Ability to get form data as variables

5
Introduction to Networking Example Server

• Example Web Server

Errors
WebBrowser
Web Server
Static
Dynamic CGI
Network
Database
Web Service
6
Introduction to Networking Example Server
WebBrowser
Httpd
ReThread
HttpOutputStream
HttpInputStream
Network
HttpProcessor processRequest()?
main()?
HttpFile
HttpCGI
HttpClass
HttpException
HttpClassProcessor
RedirectException
CGI
Echo
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Introduction to Networking Example Server

• Class HTTP (HTTP.java)?
• Default values and static variables
• public static final String METHOD_GET "GET"
• public static final String METHOD_POST
  "POST"
• public static final String METHOD_HEAD
  "HEAD"
• public static final int STATUS_OKAY 200
• public static final int STATUS_NO_CONTENT
  204
• public static final int STATUS_MOVED_PERMANENTLY
  301
• public static final int STATUS_MOVED_TEMPORARILY
  302
• public static final int STATUS_BAD_REQUEST
  400
• public static final int STATUS_FORBIDDEN 403
• public static final int STATUS_NOT_FOUND 404
• public static final int STATUS_NOT_ALLOWED
  405
• public static final int STATUS_INTERNAL_ERROR
  500
• public static final int STATUS_NOT_IMPLEMENTED
  501

8
Introduction to Networking Example Server

• Class Httpd
• Main class
• public static void main (String args) throws
  IOException
• ServerSocket server new ServerSocket
  (HTTP.PORT)
• while (true)
• Socket client server.accept ()
• Httpd httpd new Httpd (client)
• ReThread reThread new ReThread (httpd)
• reThread.start ()

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Introduction to Networking Example Server

• Class HttpInputStream
• InputStream class
• public void readRequest () throws IOException
• String request readLine ()
• if (request null)?
• throw new HttpException (HTTP.STATUS_BAD_REQ
  UEST, "Null query")
• StringTokenizer parts new StringTokenizer
  (request)
• try
• parseMethod (parts.nextToken ())
• parseRequest (parts.nextToken ())
• catch (NoSuchElementException ex)
• throw new HttpException (HTTP.STATUS_BAD_REQ
  UEST, request)
• if (parts.hasMoreTokens ())?
• parseVersion (parts.nextToken ())
• else
• ..............

10
Introduction to Networking Example Server

• Class HttpFile
• Class to deal with static files
• public HttpFile (HttpInputStream in) throws
  IOException
• if (in.getMethod () HTTP.METHOD_POST)?
• throw new HttpException (HTTP.STATUS_NOT_ALL
  OWED,
• "ltTTgt"
  in.getMethod () " " in.getPath () "lt/TTgt")
• file new File (HTTP.HTML_ROOT,
  HTTP.translateFilename (in.getPath ()))
• if (in.getPath ().endsWith ("/"))?
• file new File (file, HTTP.DEFAULT_INDEX)
• if (!file.exists ())?
• throw new HttpException (HTTP.STATUS_NOT_FOU
  ND,
• "File ltTTgt"
  in.getPath () "lt/TTgt not found.")
• if (file.isDirectory ())?
• throw new RedirectException
  (HTTP.STATUS_MOVED_PERMANENTLY,
• in.getPath ()
  "/")
• if (!file.isFile () !file.canRead ())?
• throw new HttpException (HTTP.STATUS_FORBIDD
  EN, in.getPath ())

11
Introduction to Networking Example Server

• Class HttpCGI
• Class to deal with dynamic requests
• public void processRequest (HttpOutputStream
  out) throws IOException
• ReThread drain null
• try
• if (in.getMethod () ! HTTP.METHOD_POST)
• cgi jvm.exec (cgiScript.getPath (),
  env)
• cgi.getOutputStream ().close ()
• out.write (cgi.getInputStream ())
• else
• cgi jvm.exec (cgiScript.getPath (),
  env)
• drain new ReThread (this)
• drain.start ()
• out.write (cgi.getInputStream ())

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Introduction to Networking Http Server - SSI

• HTTP Server SSI need for http to be
  stateful
• Keep in mind that http is stateless, how to we
  create state?
• CGI Allowed for dynamic passing of data
• Early state was passed as a key back and forth
  and hidden in a non-visible variable (very
  hackable)?
• SSI Server Side Includes allowed for better
  use of state information. Not as good as cookies,
  but allowed the server to Execute code with
  variables different than the CGI program
• First uses of embeded code for future things
  like ltphpgt and ltASPgt code
• Required plugin capabilities

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Introduction to Networking Http Server -
SSI/Servlet

• HTTP Server SSI Servlets
• Let the servlet deal with state information
• Used as an object way to maintain state
• Can embed variables / etc.
• Still required plugin for different web servers
• Netscape NSAPI
• Microsoft (IIS) ISAPI
• Would only run SSI through plugin module
• ltservlet
• nameServletName
• codeServletClass
• ltparam namerequestParam1 valueval3.........
  ..

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Introduction to Networking Http Server -
SSI/Servlet

• HTTP Server SSI Servlets
• Used in URL as http//servernameport/base/Servle
  tName
• Ability to use given cookie variable to identify
  client and use for state information
• Can hold object for not only static variables,
  but methods also
• Problem with SSI Servlets processing costs..
• When getting past static pages, then the cost of
  invoking a new process becomes important
• CGI requires fork/exec for every iterative
  call
• SSI requires heavier httpd daemon to process
  calls
• Servlet ability to invoke thread and hold till
  timeout

15
Introduction to Networking Http Server - Servlet

• HTTP Server Pure Servlets
• If servlet container is already in a JVM, no
  need to exec
• Apache (Jakarta) Tomcat
• Example of a pure java servlet container
• Can be run stand alone, behind other http
  server, and can talk to other tomcat servers (in
  version 5.0 and greater) to pass state
  information across for true load balancing
• Take advantage of Java architecture to implement
  java objects either through dynamic object method
  invocation or through beans
• PORTABLE
• Can take deployment archive (war file) and lay
  on any pure java web container

16
Introduction to Networking Example Server

• Questions?