Servlets

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Servlets

• CS-328
• Dick Steflik

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What is a servlet

• A Java application run on a thread of the
  webserver in response to an HTTP GET or POST
  request.
• The servlet is used to generate Dynamic HTML to
  return to the requesting browser

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The Servlet Model
HTTP Get or Post
Java Enabled Webserver
BROWSER
J V M
Servlet
HTML
Data Base
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Invoking a servlet

• ltservletgt tag
• webserver must be enabled for server side embeds
• action attribute of ltformgt tag
• can be GET or POST (HTTP 1.0)
• can also be PUT (HTTP 1.1)

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Servlets Provide

• Protocol independent and platform independent
  server side components
• A Common API (Servlet API)
• Dynamic loading either locally or over the
  network
• Security (servlet security model)
• More safe than CGI scripts
• runs as thread not as child process

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Life cycle

• Once invoked a servlet has a life cycle that is
  supported by a set of life cycle methods that are
  automatically run by the webserver
• init() - run when initially loaded
• service() - for performing the servlets service
• destroy() - for destroying the servlet object
• doGet() - only for HTTP servlets and is used for
  processing HTTP GET requests
• doPost() - only for HTTP servlets and is used for
  processing HTTP POST requests

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Servlet Interface

• All servlets must implement the Servlet interface
• Methods
• init()
• service()
• destroy()
• getServletConfig()
• getServletInfo()

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ServletConfig Interface

• Implemented by network services to pass
  configuration info to a servlet when it is first
  loaded
• Methods
• getInitParameter(String name) - returns a String
  value of the requested parameter
• getInitParameterNames() - returns an enumeration
  of the names of the initialization parameters
• getServletContext() - returns a ServerContext
  object that contains the servlets context

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ServletContext Interface

• Implemented by network services, gives servlets
  access to environmental information and allows
  logging of events.
• Methods
• getServlet() - returns an initialized and ready
  to run Servlet object.
• getServlets() - returns an enumeration of all of
  the Servlet objects in this server that are in
  the same name space (always includes the servlet
  itself)
• getServerInfo() - returns info about the network
  service the Servlet is running under
• getAttribute(String name) - returns the value of
  the named attribute
• getRealPath(String name) - returns the actual
  path of the named virtual path
• getMimeType(String file) - returns mime type of
  the named file
• log(String msg) - writes msg into the servlet log
  file

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ServletRequest Interface

• Provides means to get information from the HTTP
  request header
• Methods
• getProtocol()
• getScheme()
• getParameterNames()
• getParameter()
• getParameterValues()
• getAttribute()
• getContentLength()
• getContentType()
• getInputStream()
• getRemoteAddr()
• getRemoteHost()

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(more)

• getServerName()
• getServerPort()
• getRealPath()

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ServletResponse Interface

• Provides means to build HTTP response header
• Methods
• setContentLength(int len)
• setContentType(String type)
• getOutputStream() - returns a ServletOutputStream
  for writing the response data

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GenericServlet Class

• Abstract class that implements Servlet and
  ServletConfig

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HttpServlet Class

• Abstract class that extends GenericServlet Class
  to provide a framework for the HTTP Protocol
• doGet(HttpServletRequest req, HttpServletResponse
  resp)
• doPost (HttpServletRequest req,
  HttpServletResponse resp)
• getLastModified((HttpServletRequest req)

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HttpServletRequest Interface

• getAuthType()
• getHeaderNames()
• getHeader()
• getDateHeader()
• getIntHeader()
• getMethod()
• getQueryString()
• getRemoteUser()

• getRequestURI()
• getServletPath()
• getPathInfo()
• getPathTranslated()

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HttpServletResponse Interface

• containsHeader(String name)
• setHeader(String name,String value)
• setDateHeader(String name, long value)
• setIntHeader(String name, int value)
• setStatus(int sc)

• setStatus(int sc, String msg)
• sendError(int sc)
• sendError(int sc, String msg)
• sendRedirect(String location)

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HttpUtils Class

• getRequestURL(HttpServletRequest req)
• parsePostData(int ServletStream) - returns a hash
  table containing the name/value pairs
• parseQueryString(String s) - returns a hash table
  containing the name/value pairs