Object-Oriented Enterprise Application Development

1
Object-Oriented Enterprise Application Development

• JavaServer Pages

2
Topics

• During this class we will examine
• Anatomy of a JavaServer Page
• Merging markup with Java
• Configuring our JSPs with directives
• Integrating servlets and JSPs

3
JavaServer Pages
4
Justification

• JavaServer Pages (JSPs) are a technology that
  allow developers to mix static with dynamic
  content.
• JavaServer Pages have been successful for two (2)
  reasons
• JSPs are supported across multiple platforms.
• JSPs give developers access to all Java
  technologies instead of using a scripting
  language.

5
Roles and Responsibilities

• Although servlets can generate dynamic content,
  it's often advantageous to separate the business
  logic in the servlet from the presentation logic.
• By using JSPs we can have application programmers
  building servlets while content designers and
  graphic artists construct the JSPs.

6
Versions

• We'll use version 1.1 of the JavaServer Pages
  specification.
• The 1.0 and 1.1 version JSPs are almost totally
  incompatible with the 0.92 version of the
  specification.

7
JSP Structure
8
Basic Concepts

• At their heart, basic JSPs look just like regular
  HTML markup.
• A static HTML document can be turned into a JSP
  simply by changing its extension to .jsp.
• The key difference is that JSPs are dynamic.
• When a JSP is executed, the JSP engine converts
  that JSP into an equivalent servlet which then
  follows the normal lifecycle.

9
Sample Code - HelloWorld

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML4.0
   Transitional//EN"gt
2. lt-- comments look like this --gt
3. ltHTMLgt
4. ltHEADgt
5. ltTITLEgtHelloWorld JSPlt/TITLEgt
6. lt/HEADgt
7. ltBODYgt
8. ltH2gtHello, World!lt/H2gt
9. lt/BODYgt
10. lt/HTMLgt

10
Dynamic Content

• If all we needed was static content, then we'd
  just use HTML. The strength of JSPs lie in their
  ability to generate and manipulate dynamic
  content.
• There are three common ways of performing this
  generation using JSPs
• Expressions,
• Scriptlets
• Declarations

11
Lifecycle

• Even though JSPs are ultimately compiled into
  servlets, there are a few differences in their
  lifecycle.
• Most of the tags for generating dynamic content
  are placed within the JSP's jservice() method.
• This method is called by the JSP's service()
  method for both GET and POST requests.

12
JSP Tags
13
Basic Tags

• In the 0.92 version of the JSP specification, we
  identified dynamic content using special tags.
• In version 1.1 of the JSP specification we can
  still use some of these tags. We can also use
  equivalent XML tags.

14
JSP Expressions

• The simplest form of dynamic content is the JSP
  expression. This is used to send a value back to
  the client.
• The tag format of an expression is given by
• lt java expression gt

15
Sample Code - DynamicHelloWorld

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. ltHTMLgt
3. ltHEADgtltTITLEgt
4. DynamicHelloWorld JSP
5. lt/TITLEgtlt/HEADgt
6. ltBODYgt
7. ltH2gtHello, World!lt/H2gtltBRgt
8. ltH3gtIts now
9. lt new java.util.Date() gt
10. lt/H3gt
11. lt/BODYgt
12. lt/HTMLgt

16
Implicit Variables(1 of 3)

• There are eight (8) implicit variables for each
  JSP. The four (4) most common are
• request The HttpServletRequest object passed to
  the JSP.
• response The HttpServletResponse object passed
  to the JSP.
• session The client's HttpSession object.
• out The PrintWriter object used to send output
  to the client that initiated the request.

17
Implicit Variables(2 of 3)

• Other useful variables include
• application The ServletContext object.
• config The ServletConfig object.
• pageContect The PageContext object.
• page The this object (not currently used).

18
Implicit Variables(3 of 3)

• These implicit variable can be used within JSP
  expressions and scriptlets, but not within JSP
  declarations.

19
Sample Code Status(1 of 2)

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. ltHTMLgt
3. ltHEADgtltTITLEgt
4. StatusHelloWorld JSP
5. lt/TITLEgtlt/HEADgt
6. ltBODYgt
7. ltH2gtHello, World!lt/H2gtltBRgt
8. ltH3gtCurrent Time
9. lt new java.util.Date() gt
10. lt/H3gtltBRgt
11. ltH3gtSession ID
12. lt session.getId() gt
13. lt/H3gtltBRgt

20
Sample Code Status(2 of 2)

1. ltH3gtHostname
2. lt request.getRemoteHost() gt
3. lt/H3gtltBRgt
4. ltH3gtParameter
5. lt request.getParameter("test") gt
6. lt/H3gt
7. lt/BODYgt
8. lt/HTMLgt

21
JSP Scriptlets

• Often a single expression isn't adequate for the
  complexity of the output we want the JSP to
  generate.
• JSPs allow us to embed complete segments of Java
  code within a scriptlet.
• The tag format of a scriptlet is given by
• lt java code gt

22
Sample Code Scriptlet(1 of 2)

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. ltHTMLgt
3. ltHEADgt
4. ltTITLEgtScriptlet JSPlt/TITLEgt
5. lt/HEADgt
6. ltBODYgt
7. ltH2gtHello, World!lt/H2gtltBRgt
8. ltH3gtCurrent Time
9. lt new java.util.Date() gt
10. lt/H3gtltBRgt
11. ltH3gtSession ID
12. lt session.getId() gt
13. lt/H3gtltBRgt

23
Sample Code Scriptlet(2 of 2)

1. ltH3gtHostname
2. lt request.getRemoteHost() gt
3. lt/H3gtltBRgt
4. lt
5. String testString request.getParameter
   ("test")
6. if (null testString)
7. testString "no.such.parameter"
9. gt
10. ltH3gtParameter lt testString gtlt/H3gt
11. lt/BODYgt
12. lt/HTMLgt

24
Conditional Tags

• JSP scriptlets are useful for including
  conditional content.
• This cuts down on the amount of data returned to
  the client.
• This technique can be used to implement basic
  security features.

25
Sample Code Scriptlet (rev.)(1 of 3)

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. ltHTMLgt
3. ltHEADgt
4. ltTITLEgtScriptlet JSPlt/TITLEgt
5. lt/HEADgt
6. ltBODYgt
7. ltH2gtHello, World!lt/H2gtltBRgt
8. ltH3gtCurrent Time
9. lt new java.util.Date() gt
10. lt/H3gtltBRgt

26
Sample Code Scriptlet (rev.)(2 of 3)

1. lt
2. if (session.getId() ! null)
3. gt
4. ltH3gtSession ID
5. lt session.getId() gt
6. lt/H3gtltBRgt
7. lt
9. gt
10. ltH3gtHostname
11. lt request.getRemoteHost() gt
12. lt/H3gtltBRgt

27
Sample Code Scriptlet (rev.)(3 of 3)

1. lt
2. String testString
   request.getParameter("test")
3. if (null testString)
4. testString "no.such.parameter"
6. gt
7. ltH3gtParameter
8. lt testString gt
9. lt/H3gt
10. lt/BODYgt
11. lt/HTMLgt

28
Translated Code Scriptlet(1 of 8)

1. import javax.servlet.
2. import javax.servlet.http.
3. import javax.servlet.jsp.
4. import javax.servlet.jsp.tagext.
5. import java.io.PrintWriter
6. import java.io.IOException
7. import java.io.FileInputStream
8. import java.io.ObjectInputStream
9. import java.util.Vector
10. import org.apache.jasper.runtime.
11. import java.beans.
12. import org.apache.jasper.JasperException

29
Translated Code Scriptlet(2 of 8)

1. public class _0002fHtml_0002fscriptlet_0002ejspscr
   iptlet_jsp_0 extends HttpJspBase
2. static
3. public _0002fHtml_0002fscriptlet_0002ejspscriptlet
   _jsp_0( )
4. private static boolean _jspx_inited false
5. public final void _jspx_init() throws
   JasperException

30
Translated Code Scriptlet(3 of 8)

1. public void _jspService( HttpServletRequest
   request, HttpServletResponse response)
2. throws IOException, ServletException
3. JspFactory _jspxFactory null
4. PageContext pageContext null
5. HttpSession session null
6. ServletContext application null
7. ServletConfig config null
8. JspWriter out null
9. Object page this
10. String _value null

31
Translated Code Scriptlet(4 of 8)

1. try
2. if (_jspx_inited false)
3. _jspx_init()
4. _jspx_inited true
6. _jspxFactory JspFactory.getDefaultFact
   ory()
7. response.setContentType(
8. "text/htmlcharset8859_1")
9. pageContext _jspxFactory.getPageContex
   t( this, request, response, "",
   true, 8192, true)

32
Translated Code Scriptlet(5 of 8)

1. application pageContext.getServletCont
   ext()
2. config pageContext.getServletConfig()
   
3. session pageContext.getSession()
4. out pageContext.getOut()
5. out.write("lt!DOCTYPE HTML PUBLIC
   \"-//W3C//DTD HTML 4.0 Transitional//EN\"gt\r\nltHT
   MLgt\r\n ltHEADgt\r\n ltTITLEgtScriptlet
   JSPlt/TITLEgt\r\n lt/HEADgt\r\n
   ltBODYgt\r\n\t\t\tltH2gtHello, World!lt/H2gt\tltBRgt\r\n\t
   \t\tltH3gtCurrent Time ")

33
Translated Code Scriptlet(6 of 8)

1. out.print( new java.util.Date() )
2. out.write("lt/H3gt\r\n\t\t\t"-ltBRgt\r\n\t\t\t")
   
3. if (session.getId() ! null)
4. out.write("\r\n\t\t\t\tltH3gt"-Session ID
   ")
5. out.print( session.getId() )
6. out.write("lt/H3gtltBRgt\r\n\t\t\t")
8. out.write("\r\n\t\t\tltH3gt"-Hostname ")
9. out.print( request.getRemoteHost() )
10. out.write("lt/H3gtltBRgt\r\n\t\t\t")

34
Translated Code Scriptlet(7 of 8)

1. String testString request.getParameter
   ("test")
2. if (null testString)
3. testString "no.such.parameter"
5. out.write("\r\n\t\t\tltH3gt"-Parameter ")
6. out.print( testString )
7. out.write("lt/H3gt\r\n\tlt/BODYgt"-\r\nlt/HTMLgt")

35
Translated Code Scriptlet(8 of 8)

1. catch (Exception ex)
2. if (out.getBufferSize() ! 0)
3. out.clearBuffer()
4. pageContext. handlePageException(ex)
   
5. finally
6. out.flush()
7. _jspxFactory. releasePageContext(pageCon
   text)

36
JSP Declarations

• A JSP declaration exists outside of the
  jservice() method.
• This means that code in a declaration cannot make
  use of the implicit variables.
• This allows us to declare JSP-level variables and
  methods.
• The tag format of an expression is given by
• lt! java declaration gt

37
Sample Code Declaration(1 of 2)

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. ltHTMLgt
3. ltHEADgt
4. ltTITLEgtDeclaration JSPlt/TITLEgt
5. lt/HEADgt
6. ltBODYgt
7. ltH2gtDeclarationslt/H2gtltBRgt
8. ltH3gtCurrent Time
9. lt new java.util.Date() gt
10. lt/H3gtltBRgt
11. ltH3gtSession ID
12. lt session.getId() gt
13. lt/H3gtltBRgt

38
Sample Code Declaration(2 of 2)

1. ltH3gtHostname
2. lt request.getRemoteHost() gt
3. lt/H3gtltBRgt
4. lt! private int accesses 0 gt
5. ltH3gt
6. lt accesses gt
7. Accesses to the page since JSP was
   loaded.
8. lt/H3gt
9. lt/BODYgt
10. lt/HTMLgt

39
JSP Directives
40
Overview

• We use directives to customize the JSP's
  behavior. Each directive affects the structure of
  the servlet resulting from the JSP's compilation.
• There are three (3) types of directives
• page Controls the servlet's structure.
• include Inserts a file into the servlet class.
• taglib Defines custom markup tags.

41
Page Directives

• There are many page directives. We'll look at a
  few of the most common attributes
• import
• isThreadSafe
• session
• errorPage
• We use the directive tag to indicate that we want
  a directive to take effect
• lt_at_ directive gt

42
Import Attribute

• The import attribute allows a JSP to import class
  libraries
• lt_at_ page import"java.util." gt
• By default a JSP automatically imports
• java.lang.
• java.servlet.
• java.servlet.http.
• java.servlet.jsp.

43
Sample Code - Import

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. lt_at_ page importjava.util.Date gt
3. ltHTMLgt
4. ltHEADgt
5. ltTITLEgtImport JSPlt/TITLEgt
6. lt/HEADgt
7. ltBODYgt
8. ltH2gtImportslt/H2gtltBRgt
9. ltH3gtCurrent Time
10. lt new Date() gt
11. lt/H3gt
12. lt/BODYgt
13. lt/HTMLgt

44
isThreadSafe Attribute

• The isThreadSafe attribute forces the JSP's
  servlet to implement the SingleThreadedModel
  interface
• lt_at_ page isThreadSafe"true" gt
• By default a JSP is assumed to be thread safe in
  the same way that servlets are.
• If this isn't the case you can
• Make it thread-safe using synchronized blocks
• Set isThreadSafe to false.

45
Sample Code IsThreadSafe(1 of 2)

1. lt! private int id 0 gt
2. lt
3. String userId "id" id
4. out.println("Your id is " id)
5. id
6. gt

46
Sample Code IsThreadSafe(2 of 2)

1. lt! private int id 0 gt
2. lt
3. synchronized (this)
4. String userId "id" id
5. out.println("Your id is " id)
6. id
8. gt

47
Sample Code - IsThreadSafe

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. lt_at_ page importjava.util.Date gt
3. lt_at_ page isThreadSafefalse gt
4. ltHTMLgt
5. ltHEADgt
6. ltTITLEgtSingle Thread JSPlt/TITLEgt
7. lt/HEADgt
8. ltBODYgt
9. lt! private int accesses 0 gt
10. lt accesses gt
11. Accesses since JSP was loaded.
12. lt/BODYgt
13. lt/HTMLgt

48
Session Attribute

• The session attribute controls whether or not the
  JSP can access the client's session
• lt_at_ page session"true" gt
• By default a JSP participates in the client's
  session.
• lt_at_ page session"true" gt
• If this isn't the behavior we want, we can turn
  it off
• lt_at_ page session"false" gt

49
errorPage Attribute

• The errorPage attribute specifies the URL to
  which the client will be sent if an unhandled
  exception is encountered
• lt_at_ page errorPage"some URL" gt
• The exception that caused the problem will be
  provided to the page via the exception variable.

50
Sample Code - ErrorPage

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. lt_at_ page errorPageerror.jsp gt
3. ltHTMLgt
4. ltHEADgt
5. ltTITLEgtErrorPage JSPlt/TITLEgt
6. lt/HEADgt
7. ltBODYgt
8. ltH3gtSession Variable
9. lt
10. session.
11. getAttribute("var").toString()
12. gt
13. lt/BODYgt
14. lt/HTMLgt

51
Integrating Servlets and JavaServer Pages
52
Integration

• JavaServer Pages allow graphic designers to
  achieve reasonable separation between their roles
  and the role of the servlet developer.
• However, since all of these components will be
  used together in the final application, we need
  to integrate them.

53
Request Dispatcher

• We've already looked at one approach to
  integrating servlets and JSPs the
  RequestDispatcher class.
• This remains the simplest way of invoking a JSP
  from a servlet.

54
Shared Data

• It isn't uncommon to need to share data between a
  servlet and a JSP.
• The servlet may perform all of the business
  processing necessary to generate the data to be
  displayed by the JSP.
• We could use the client's session, but what if
  the data isn't required beyond a single
  request-response pair?

55
Request Attributes(1 of 2)

• For data that needs to exist only for a single
  client request, we can use the HttpServletRequest
  object to store our data.
• In addition to the parameters passed in by the
  client, the HttpServletRequest contains
  attributes which can be set by servlets and JSPs.

56
Request Attributes(2 of 2)

• As with session attributes, request attributes
  are nothing more than a name-value pair.
• To manipulate these attributes you can use the
  following methods
• public void
• setAttribute(String, Object)
• public Object
• getAttribute(String)

57
Sample Code SetData(1 of 3)

1. import java.io.
2. import java.util.
3. import javax.servlet.
4. import javax.servlet.http.
5. public class SendData
6. extends HttpServlet
7. public void doPost(HttpServletRequest rqst,
   HttpServletResponse resp)
8. throws ServletException, IOException
9. doGet(rqst, resp)

58
Sample Code SetData(2 of 3)

1. public void doGet(HttpServletRequest rqst,
   HttpServletResponse resp)
2. throws ServletException, IOException
3. rqst.setAttribute("parm", "skippy")
4. chain(rqst, resp, "GetData.jsp")

59
Sample Code SetData(3 of 3)

1. private void chain(HttpServletRequest rqst,
   HttpServletResponse resp, String
   URL)
2. throws ServletException, IOException
3. RequestDispatcher dispatcher
   getServletContext(). getRequestDispatcher(
   URL)
4. dispatcher.forward(rqst, resp)

60
Sample Code - GetData

1. lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
   Transitional//EN"gt
2. ltHTMLgt
3. ltHEADgt
4. ltTITLEgtGetData JSPlt/TITLEgt
5. lt/HEADgt
6. ltBODYgt
7. ltH2gtGet Shared Valuelt/H2gtltBRgt
8. ltH3gtThe shared value is...
9. lt request.getAttribute("parm") gt
10. lt/H3gt
11. lt/BODYgt
12. lt/HTMLgt

61
Review

• During this class we have discussed
• Anatomy of a JavaServer Page
• Merging markup with Java
• Configuring our JSPs with directives
• Integrating servlets and JSPs

62
Resources

• Core Servlets and JavaServer PagesMarty Hall,
  Prentice-Hall, Inc., 2000.ISBN 0-13-089340-4
• Java 2 Platform, Enterprise EditionB. Shannon,
  et al., Addison-Wesley, 2000.ISBN 0-201-70456-0

63
Coming Attractions

• Next week we'll add custom tags to our JavaServer
  Pages.
• Please read Chapter 14 in your text.