Servlet and JSP Programming: An Introduction

1
Servlet and JSP ProgrammingAn Introduction

• Spiros Papadimitriou
• spapadim_at_cs.cmu.edu

2
Overview

• Introduction
• Static vs. Dynamic
• Servlets
• Java Server Pages (JSP)

3
Introduction

• What you know
• Java
• JDBC
• What well tell you
• How to use Java inside a webserver!
• Why you might care
• Building non-trivial web interfaces and
  applications
• In particular database-backed web applications

4
Plain Old Static Pages

• Static webpages
• Plain files stored in the filesystem
• Webserver accepts pathnames
• Returns contents of corresponding file
• Boring!
• Cant generate customized contentalways serve
  the same static pages

5
Static Pages
6
Dynamic Content

• CGI Easy fix
• Common Gateway Interface
• Oldest standard
• But at least a standard!
• Inefficient
• No persistent state
• Forward requests to external programs
• Spawn one process for each new request (ouch!)
• Communicate via
• Standard input/output
• Environment variables
• Process terminates after request is handled

7
CGI
8
CGI
9
Servlets to the rescue

• Little Java programs
• Contain application-specific code
• Web server does generic part of request handling
• Servlets run in the web server and do some of
  the handling
• Highlights
• Standard!
• Efficiency (much better than CGI)
• Security (Java!)
• Persistence (handle multiple requests)

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Servlets
STATUS ltresponse foogt
res ltrespose foogt
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Servlets
res ltresponse bargt
STATUS ltresponse bargt
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Servlet Example

• package pkg
• import java.io.
• import javax.servlet.
• import javax.servlet.http.
• public class Servlet extends HttpServlet
• public void doGet(HttpServletRequest req,
• HttpServletResponse res)
• throws IOException, ServletException
• res.setContentType("text/html")
• PrintWriter out res.getWriter()
• out.println("lthtmlgtltheadgtlttitlegtSample
  Servlet")
• out.println("lt/titlegtlt/headgtltbodygt")
• out.println("lth1gtHello World at "
• req.getRequestURI() "
  !lt/h1gt")
• out.println(ltpgtKey is "
  req.getParameter("KEY"))
• out.println(lt/pgtlt/bodygtlt/htmlgt")

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More Servlets

• A catalog of servlet methods
• init(config)
• service(req, res)
• doGet(req, res)
• doPut(req, res)
• doDelete(req, res)
• etc
• A catalog of request methods
• getParameter(name)
• getParameterNames(), getParameterValues(name)
• getCookies()
• A catalog of response methods
• sendRedirect(url), sendError(errCode, errStr)
• setContentType(mimeType)
• addCookie(cookieObj)

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JSP Sugar

• Printing to output not really a special case when
  writing heaps of HTML!
• Well why not make that the common case in the
  syntax and program statements the special case?
• And while were at it, why not hide the
  compilation steps (let the server do it)?
• Now things look more like plain old HTML (only
  they arent they can produce dynamic content and
  really are Java programs)

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First JSP Example (1/3)

• lt_at_ page importjava.io. gt
• lthtmlgt
• ltheadgtlttitlegtSample JSPlt/titlegtlt/headgt
• lt String s JSP gt
• ltbodygt
• lth1gtHello lt s gt World!lt/h1gt
• ltpgtlt out.print(Scriptlet Statement Hello!)
  gtlt/pgt
• ltpgtKey is lt request.getParameter(KEY) gtlt/pgt
• lt/bodygt
• lt/htmlgt
• Core syntactic elements
• Directives lt_at_ page gt
• Declarations lt! gt (outside service method)
• Scriptlets lt gt
• Expressions lt gt

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First JSP Example (2/3)

• package jsp._jsp
• // line/jsp/hello.jsp1
• import java.io.
• import javax.servlet.
• import javax.servlet.http.
• import javax.servlet.jsp.
• public class _hello_2ejsp
• extends org.gjt.jsp.HttpJspPageImpl
• implements org.gjt.jsp.GnuJspPage
• public void _jspService (HttpServletRequest
  request,
• HttpServletResponse
  response)
• throws ServletException, java.io.IOException
• response.setContentType ("text/html")
• HttpSession session pageContext.getSession
  ()

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First JSP Example (3/3)
try // line/jsp/hello.jsp2
out.print("lthtmlgt\n") //
line/jsp/hello.jsp4 String s "GNUJSP"
// line/jsp/hello.jsp5
out.print("\nltbodygt") //
line/jsp/hello.jsp6 out.print(s)
// line/jsp/hello.jsp7
out.print(Scriptlet Statement Hello!)
// line/jsp/hello.jsp8
out.print(request.getParameter(KEY)) //
line/jsp/hello.jsp8 out.print(lt/pgt\nlt/bod
ygt) catch (Throwable e)
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Second JSP Example (1/2)

• lt_at_ page importjava.io. gt
• lt_at_ page importjava.util. gt
• lt_at_ page importjava.sql. gt
• lt!
• Static final String dbHost gt
• Static final String oracleDriver
• gt
• lt
• String courseId request.getParameter(courseid
  )
• Class.forName(oracleDriver)
• Connection conn DriverManager.getConnection()
  
• Statement stmt con.createStatement()
• String qry SELECT STUDENT.SID, SNAME,
  COURSE.CID
• FROM STUDENT, COURSE, TAKE
• WHERE TAKE.CID courseId
  AND
• STUDENT.SID TAKE.SID AND
• COURSE.CID TAKE.CID
• ResultSet res conn.executeQuery(qry)
• gt

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Second JSP Example (2/2)

• lthtmlgt
• ltheadgtlttitlegtStudent Informationlt/titlegtlt/headgt
• ltbodygt
• lth1gtStudent Information for lt courseId gtlt/h1gt
• ltpgtlttable border1gt
• lttrgtltthgtCourseIDlt/thgtltthgtStudentlt/thgtltthgtStudentID
  lt/thgtlt/trgt
• lt while (rs.next()) gt
• lttrgt
• lttdgtlt rs.getString(cid) gtlt/tdgt
• lttdgtlt rs.getString(sname) gtlt/tdgt
• lttdgtlt rs.getString(sid) gtlt/tdgt
• lt/trgt
• lt // end while gt
• lt/tablegtlt/pgt
• lt/bodygt
• lt/htmlgt

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Alternatives

• Dynamically loadable server modules
• Web server offers standard API for request
  handlers
• Request handlers are dynamic libraries
• Loaded into server address space (security?!)
• Very efficient!
• Better suited for generic server extensions than
  application-specific logic
• CGI flavors
• Persistent CGI (PCGI) / FastCGI
• Too little, too late
• Modern web publishing systems
• Essentially databases that speak HTTP

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More Information

• Servlets and JSPs
• http//java.sun.com/products/servlet/
• http//java.sun.com/products/jsp/
• JDBC
• http//java.sun.com/products/jdbc/