Servlets and JavaServer Pages JSP

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Lecture 5

• Servlets and JavaServer Pages (JSP)

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Servlet?

• A Servlet is a Java class that provides special
  server side service.
• Servlets runs in a server and returns answer to
  clients in a web page.
• Servlets build webpages....so, its contains HTML
  

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Servers jobb
Read data sent by client Generate the
results Send data back to client (HTML)
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How its works

• init
• Executed once when the servlet is first loaded.
• Not called for each request.
• service
• Called in a new thread by server for each
  request.
• Dispatches to doGet, doPost, etc.
• Do not override this method!
• doGet, doPost
• Handles GET, POST, etc. requests.
• Override these to provide desired behavior.
• destroy
• Called when server deletes servlet instance.
• Not called after each request.

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Structure

• import java.io.import java.net.import
  javax.servlet.import javax.servlet.http.publ
  ic class GetOrder extends HttpServlet
  public void doGet( HttpServletRequest request,
  HttpServletResponse response) throws
  ServletException, IOException
• response.setContentType("text/html
  charsetUTF-8") PrintWriter out
  response.getWriter() String
  message1request.getParameter("Order")
  //TODO output your page here
  out.println("lthtmlgt") out.println("ltheadgt
  ") out.println("lttitlegtorderlt/titlegt")
  out.println("lt/headgt")
  out.println("ltbodygt") out.println("lth1gtlts
  tronggtI like to order ltbrgtGet Order Servlet
  lt/h1gt") out.println("lt/bodygt")
  out.println("lt/htmlgt")
  out.close()

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How its works

• public void doGet( HttpServletRequest request,
• HttpServletResponse response)
• ..
• -HTLM forms let the user submit data to romote
  site
• - Servlets use HTTP proprieties, request ,
  respons to comunicate
• Request, incapsulate data from the client
• Respons, incapsulate the response information
  from the server

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Use form and html to conect ...

• lthtmlgt
• ltheadgtlttitlegtGet Orderlt/titlegtlt/headgt
• ltbodygt
• lth3gtEnter an orderlt/h3gt
• ltform action"http//localhost8100/servlet/GetOrd
  er"
• 
  methodGETgt
• Order ltinput typetext nameOrder size20gt
• lt/formgtlt/bodygtlt/htmlgt

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Varför inte

• Det är dålig design att ha ett objekt som har
  flera olika uppgifter, till exempel att hantera
  indata och generera utdata.
• Det är dålig design att blanda olika språk (java
  och html) i samma fil.
• Det är dålig uppdelning i roller att blanda html
  och java eftersom det ofta inte är samma person
  som hanterar båda.
• Det är ett elände att få html-strängar genom
  kompilatorn på grund av radbrytningar och
  "-tecken.
• Det går inte att använda något verktyg för att
  skriva html-sidor.

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• JSPs are essential an HTML page with special JSP
  tags embedded.
• These JSP tags can contain Java code.
• The JSP file extension is .jsp rather than .
• The JSP engine parses the .jsp and creates a Java
  servlet source file.
• HTML from the Servlet output is sent via the
  Internet.
• HTML results are displayed on the user's web
  browser.

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Structure

• lthtmlgt
• ltheadgt
• lttitlegtMy first JSP page
• lt/titlegt
• lt/headgt
• ltbodygt
• lt_at_ page language"java" gt
• lt out.println("Hello World") gt
• lt/bodygt
• lt/htmlgt

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Using JSP tags

• Declaration tag
• Expression tag
• Directive tag
• Scriptlet tag
• Action tag

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• 1) Declaration tag ( lt!  gt ) . This tag allows
  the developer to declare variables or methods.
• lt!
•           private int counter 0
•           private String get Account ( int
  accountNo)
• gt
• 2) Expression tag ( lt   gt) This tag allows
  the developer to embed any Java expression and is
  short for out.println().
• Date lt new java.util.Date() gt will print
  the date

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• 3) Directive tag ( lt_at_ directive ... gt)
•  
• A JSP directive gives special information about
  the page to the JSP Engine.
• Directives do not produce any visible output when
  the page is requested but
• change the way the JSP Engine processes the file.
•  
• There are three main types of directives
•  
• 1)     page - processing information for this
  page. lt_at_ page language "java" gt
• 2)     Include - files to be included. lt_at_
  include file "include/privacy.html" gt
• 3)     Tag library - tag library to be used in
  this page. lt_at_ taglib uri "tag library
• URI" prefix "tag Prefix" gt
•  

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• 4) Scriptlet tag ( lt ... gt )
•  Between lt and gt tags,any valid Java code is
  called a Scriptlet..   
• lt 
•         String username "visualbuilder"
•         out.println ( username )
•   gt
• 5) Action tag
•  
•   There are three main roles of action tags
•  
• 1)     enable the use of server side Javabeans
• 2)     transfer control between pages
• 3)     browser independent support for applets.

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• JSP compared to ASP
• JSP and ASP are fairly similar in the
  functionality that they provide. JSP may have
  slightly higher learning curve. Both allow
  embedded code in an HTML page,session variables
  and database access and manipulation. Whereas ASP
  is mostly found on Microsoft platforms i.e.
  NT,JSP can operate on any platform that conforms
  to the J2EE specification. JSP allow component
  reuse by using Javabeans and EJBs. ASP provides
  the use of COM / ActiveX controls.
•  
• JSP compared to ASP.NET
• ASP.NET is based on the Microsoft .NET
  framework. The .NET framework allows
  applications to be developed using different
  programming languages such as Visual Basic,C and
  JavaScript. JSP and Java still has the advantage
  that it is supported on many different platforms
  and the Java community has many years of
  experience in designing and developing Enterprise
  quality scalable applications. This is not to say
  that ASP.NET is bad,actually it is quite an
  improvement over the old ASP code.
•