Java Servlets

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Java Servlets

• Joe Komar

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Servlets Overview

• Java programs
• Stored and executed on the server
• Additional helper classes
• Part of javax.servlet java.servlet.http API
• Memory resident
• Server needs to support it
• Can have persistent connection to a database
• Can do servlet chaining
• SDK from Sun needed

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A Simple Servlet - HTML
lthtmlgt ltheadgtltTitlegtKomar's first
servletlt/titlegtlt/headgt ltbodygt ltform
actionhttp//140.209.124.1078080/servlet/JAK1
methodPOSTgt Enter your name ltinput typetext
namenamegtltbrgtltbrgt Enter your favorite movie
ltinput typetext namemoviegtltbrgt ltbrgtThanks! ltinpu
t typesubmitgt lt/formgt lt/bodygt lt/htmlgt
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A Simple Servlet - Browser Screen
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A Simple Servlet - The Code
import java.io. import javax.servlet. import
javax.servlet.http.
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A Simple Servlet - The Code
public class JAK_Servlet1 extends HttpServlet
public void doPost (HttpServletRequest req,
HttpServletResponse res)
throws ServletException,
IOException ServletOutputStream out
res.getOutputStream() res.setContentType(
"text/html") String name
req.getParameter("name") String movie
req.getParameter("movie")
out.println("lthtmlgtltheadgtlttitlegtMovieslt/titlegtlt/he
adgt") out.println("ltbodygtlth1gtWhat you
said....lt/h1gtlthrgt") out.println("ltpgtName
" name) out.println("ltpgtMovie "
movie) out.println("lt/bodygtlt/htmlgt")
out.close()
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A Simple Servlet -- Output
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Servlet Development at UST

• Create the Form (or Java Applet)
• Action POST 140.209.124.1078080/servlet/servlet
  name
• FTP it to the server
• IP address 140.209.124.107
• Username -- class (case sensitive)
• Password -- skeeter (case sensitive)
• Change to public_html directory, then to your
  directory (three initials)
• Put HTML file there

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Servlet Development at UST

• Check out your form -- 140.209.124.1078080/initia
  ls/pagename.html
• Write your servlet (put package initials as the
  first line) and compile it
• Move the .class file to the server
• Same IP, username, and password
• Change to servlets directory, then your
  subdirectory (initials) and put it there

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Servlet Development at UST

• Register your servlet on the server
• From browser, enter address 140.209.124.1079090
• Login as user admin, password testitout
• Make sure Web Service is highlighted then click
  on Manage
• Click on Servlets button on top of page
• Click on Add choice in list

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Servlet Development at UST

• Registering your servlet (continued)
• The Name field is the name you use in your
  forms Action attribute -- e.g., JAK1
• The class is the name of the class file you
  transferred with your initials, period prepended
  and without the .class extension -- e.g.,
  jak.JoeOne
• Click on the Add button
• Enter whatever you want in the description
• Click on Save
• Close the Web Service window
• Click on the Log Out button

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Servlet Development at UST

• Check out your Form/servlet application
• Hints
• Make sure you type things like the name of the
  class correctly on the server
• Keep the FTP session open when you check things
  out -- will probably have to make changes and FTP
  things again
• Make sure you hit the Reload or Refresh buttons
  after FTP changes
• Dont go changing other server settings!!

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Servlet Assignment

• Create an HTML form that has the following
• Text box for Operator ( - /) (select box??)
• Two text boxes for operands
• Submit button
• Action is a POST to a named servlet
• Write the Java Servlet
• Takes the operation and operand, performs the
  requested operation
• Creates a web page to show the inputs and results

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Servlet JDBC Example - HTML
lthtmlgt ltheadgtltTitlegtKomar's Directory
Servletlt/titlegtlt/headgt ltbodygt ltform
actionhttp//140.209.124.1078080/servlet/JAK3
methodPOSTgt Enter the name or a portion thereof
ltinput typetext namenamegtltbrgtltbrgt ltbrgtThanks! lti
nput typesubmitgt lt/formgt lt/bodygt lt/htmlgt
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Servlet JDBC Example - Browser
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Servlet JDBC Example - Servlet
package jak import java.io. import
javax.servlet. import javax.servlet.http. impo
rt java.sql.
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Servlet JDBC Example - Servlet
public class JAK_Directory extends HttpServlet
public void doPost (HttpServletRequest req,
HttpServletResponse res)
throws ServletException,
IOException ServletOutputStream out
res.getOutputStream() res.setContentType("
text/html") String name
req.getParameter("name")
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Servlet JDBC Example - Servlet
String url "jdbcodbcDirectory" String query
"select from STUDIR where Name like "
"'" name "'" Statement
stmt Connection con try
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver") c
atch (java.lang.ClassNotFoundException e)
System.err.print("Driver class not found")
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Servlet JDBC Example - Servlet
try con DriverManager.getConnection(url)
stmt con.createStatement() ResultSet
rs stmt.executeQuery(query)
out.println("lthtmlgtltheadgtlttitlegtQuery
Resultlt/titlegtlt/headgt") out.println("ltcentergt
lth1gtResults of query for " "'" name
"'lt/h1gtlt/centergt") out.println("lthrgt")
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Servlet JDBC Example - Servlet
while (rs.next()) out.println("ltpgtNam
e " rs.getString(1))
out.println("ltbrgtUsername " rs.getString(2))
out.println(" College Code "
rs.getString(3)) stmt.close()
con.close() catch(Exception ex)
System.err.print("SQL Exception "
ex.getMessage())
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Servlet JDBC Example - Output
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Core Servlet Interfaces and Class

• Servlet interface
• Methods all servlets must implement
• Typically extend GenericServlet or HttpServlet
  classes
• Server initializes the servlet with the init()
  method, asks for services with the service()
  method, destroys a it with the destroy() method
• getServletConfig() and getServletInfo()

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Core Servlet Interfaces and Class

• ServletConfig interface
• access to configuration data
• getInitParameter(name) -- value of parameter
• getInitParamenterNames() -- Enumeration of
  parameter names
• getServerContext() -- returns a ServletContext
  object

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Core Servlet Interfaces and Class

• ServletContext interface
• access to information about the environment
• getAttribute(name) -- value of the named
  attribute of the network service
• getMimeType(file) -- MIME type of the specified
  file
• getRealPath(virtual-path) -- returns real path
• getServerInfo() -- name version of server
• getServlet(name) -- servlet named
• getServlets() -- Enumeration of Servlets objects

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Core Servlet Interfaces and Class

• GenericServlet class
• implements Servlet and ServletConfig interfaces
• provides init(), destroy(), ServletConfig
  methods, and log() method
• must override and implement the service() method

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Core Servlet Interfaces and Class

• ServletRequest interface
• access data passed from the client to the servlet
• contains parameter names, parameter values,
  attributes, and a ServletInputStream
• getInputStream() -- returns a ServletInputStream
  object for reading the request body
• many other methods to get information about the
  request and its context

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Core Servlet Interfaces and Class

• ServletResponse interface
• to return response data to client
• getOutputStream() -- returns an output stream to
  write to
• setContentLength() -- sets content length for the
  response
• setContentType() -- sets the content type for the
  response

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Core Servlet Interfaces and Class

• ServletInputStream class
• readLine() -- to read into an array of bytes
• ServletOutputStream class
• overloaded print() and println() methods available

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HTTP Servlet Interfaces and Classes

• HttpServlet abstract class
• extends GenericServlet
• your class extends this one and override at least
  one method
• doPost() and doGet() most commonly overridden
• to support HTTP 1.1 commands (OPTION, PUT,
  DELETE, TRACE), override the service() method

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HTTP Servlet Interfaces and Classes

• HttpServletRequest interface
• inherits from ServletRequest
• methods to extract HTTP header information
• getDateHeader(), getHeaderNames(), getPathInfo(),
  getRemoteUser(), etc.
• getParameter(name) -- returns the String value of
  the named parameter

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HTTP Servlet Interfaces and Classes

• HttpServletResponse interface
• inherits from ServletResponse
• variables for error standard error conditions
• most of the response header information is
  standard and need not change

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HTTP Servlet Interfaces and Classes

• HttpUtils class
• collection of HTTP utility methods
• getRequestURL() -- URL of the HttpServletRequest
  object
• parsePostData() -- returns POSTs form data in a
  Hashtable
• parseQueryString() -- returns a Hashtable of
  name/value pairs