1 / 59

JSP – Java Server Pages Part 1

JSP – Java Server Pages Part 1. Representation and Management of Data on the Internet. Introduction. What is JSP Good For?. Servlets allow us to write dynamic Web pages Easy access to request, session and context data Easy manipulation of the response (cookies, etc.) And lots more...

damisi
Télécharger la présentation

JSP – Java Server Pages Part 1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. JSP – Java Server PagesPart 1 Representation and Management of Data on the Internet

  2. Introduction

  3. What is JSP Good For? • Servlets allow us to write dynamic Web pages • Easy access to request, session and context data • Easy manipulation of the response (cookies, etc.) • And lots more... • It is not convenient to write and maintain long static HTML using Servlets out.println("<h1>Bla Bla</h1>" + "bla bla bla bla" + "lots more here...")

  4. JSP Idea • Use HTML for most of the page • Write Servlet code directly in the HTML page, marked with special tags • The server automatically translates a JSP page to a Servlet class and the latter is actually invoked • In Tomcat 5.0, you can find the generated Servlet code under $CATALINA_BASE/work/

  5. Relationships • Servlets: HTML code is printed in Java code • JSP: Java code is embedded in HTML code Java HTML Java HTML

  6. Example <html> <head> <title>Hello World</title> </head> <body> <h2><%= new java.util.Date() %></h2> <h1>Hello World</h1> </body> </html> Tomcat 5.0 Generated Servlet

  7. Sun Specifications Apache Implementation Generated Servlet Generated Servlet Hierarchy(Tomcat 5.0 Implementation)

  8. JSP Limitations and Advantages • JSP can only do what a Servlet can do • Easier to write and maintain HTML • Easier to separate HTML from code • Can use a "reverse engineering technique": create static HTML and then replace static data with Java code

  9. JSP Life Cycle

  10. JSP Life Cycle The following table describes the life cycle of JSP generated Servlet in details:

  11. JSP Life Cycle Written by Marty Hall. Core Servlets & JSP book: www.coreservlets.com

  12. JSP Translation • When the JSP file is modified, JSP is translated into a Servlet • Application need not be reloaded when JSP file is modified • Server does not generate the Servlet class after startup, if the latter already exists • Generated Servlet acts just like any other Servlet

  13. init() and destroy() • init() of the generated Servlet is called every time the Servlet class is loaded into memory and instantiated • destroy() of the generated Servlet is called every time the generated Servlet is removed • The latter two happen even if the reason is modification of the JSP file

  14. Thread Synchronization • After the Servlet is generated, one instance of it serves requests in different threads, just like any other Servlet • In particular, the service method (_jspService) may be executed by several concurrent threads • Thus, like Servlets, JSP programming requires concurrency management

  15. Basic JSP Elements

  16. Basic Elements in a JSP file • HTML code: <html-tag>content</html-tag> • JSP Comments: <%-- comment --%> • Expressions: <%= expression %> • Scriptlets: <% code %> • Declarations: <%! code %> • Directives: <%@ directive attribute="value" %> • Actions: <jsp:forward.../>, <jsp:include.../> • EL Expressions: ${expression} Covered Later...

  17. JSP Expressions • A JSP expression is used to insert Java values directly into the output • It has the form: <%= expression %>, where expression can be a Java object, a numerical expression, a method call that returns a value, etc... • For example: <%= new java.util.Date() %> <%= "Hello"+" World" %> <%= (int)(100*Math.random()) %>

  18. JSP Expressions • A JSP Expression is evaluated • The result is converted to a string • The string is inserted into the page • This evaluation is performed at runtime (when the page is requested), and thus has full access to information about the request, the session, etc...

  19. public void _jspService(HttpServletRequest request, HttpServletResponse response) throws java.io.IOException, ServletException { ... response.setContentType("text/html"); ... out.write("<h1>A Random Number</h1>\r\n"); out.print( Math.random() ); out.write("\r\n"); ... } Expression Translation <h1>A Random Number</h1> <%= Math.random() %>

  20. Predefined Variables (Implicit Objects) • The following predefined variables can be used: • request: the HttpServletRequest • response: the HttpServletResponse • session: the HttpSession associated with the request • out: the PrintWriter (a buffered version of type JspWriter) used to fill the response content • application: The ServletContext • These variables and more will be discussed in details

  21. <html> <head> <title>JSP Expressions</title> </head> <body> <h2>JSP Expressions</h2> <ul> <li>Current time: <%= new java.util.Date() %></li> <li>Your hostname:<%= request.getRemoteHost() %></li> <li>Your session ID: <%= session.getId() %></li> <li>The <code>testParam</code> form parameter: <%= request.getParameter("testParam") %></li> </ul> </body> </html>

  22. JSP Scriplets • JSP scriptletslet you insert arbitrary code into the Servlet service method ( _jspService) • Scriptlets have the form: <% Java Code%> • The code is inserted verbatim into the service method, according to the location of the scriplet • Scriptlets have access to the same automatically defined variables as expressions

  23. Scriptlet Translation <%= foo() %> <% bar(); %> public void _jspService(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ... response.setContentType("text/html"); ... out.print(foo()); bar(); ... }

  24. An Interesting Example Scriptlets don't have to be complete code blocks: <%if (Math.random() < 0.5) { %> You <b>won</b> the game! <%} else { %> You <b>lost</b> the game! <% } %> if (Math.random() < 0.5) { out.write("You <b>won</b> the game!"); } else { out.write("You <b>lost</b> the game!"); }

  25. JSP Declarations • A JSP declaration lets you define methods or members that get inserted into the Servlet class (outside of all methods) • It has the following form: <%! Java Code %> • For example: <%! private int someField = 5; %> <%! private void someMethod(...) {...} %> • It is usually of better design to define methods in a separate Java class...

  26. Declaration Example • Print the number of times the current page has been requested since the Servlet initialization: <%! private int accessCount = 0; %> <%! private synchronized int incAccess() { return ++accessCount; } %> <h1>Accesses to page since Servlet init: <%= incAccess() %> </h1>

  27. public class serviceCount_jsp extends... implements... throws... { private int accessCount = 0; private synchronized int incAccess() { return ++accessCount; } public void _jspService(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ... ... out.write("<h1>Accesses to page since Servlet init: "); out.print(incAccess()); ... } ... }

  28. jspInit and jspDestroy • In JSP pages, like regular Servlets, we sometimes want to implement init and destroy • It is illegal to use JSP declarations to override init or destroy, since they are (usually) already implemented by the generated Servlet • Instead, override the methods jspInit and jspDestroy • The generated servlet is guaranteed to call these methods from init and destroy,respectively • The standard versions of jspInit and jspDestroy are empty (placeholders for you to override)

  29. JSP Directives • A JSP directive affects the structure of the Servlet class that is generated from the JSP page • It usually has the following form: <%@directive attribute1="value1"... attributeN="valueN"%> • Three directives: page, include and taglib • include and taglib will be discussed later

  30. page-Directive Attributes • importattribute: A comma separated list of classes/packages to import <%@ page import="java.util.*, java.io.*" %> • contentTypeattribute:Sets the MIME-Type of the resulting document (default is text/html) <%@ page contentType="text/plain" %> • What is the difference between setting the contentType attribute, and writing <%response.setContentType("...");%> ?

  31. More page-Directive Attributes • session="true|false" - use a session? • buffer="sizekb|none" • Specifies the content-buffer size (out) • autoFlush="true|false" • Specifies whether the buffer should be flushed when it fills, or throw an exception otherwise • isELIgnored ="true|false" • Specifies whether JSP expression language is used • EL is discussed later

  32. Variables in JSP

  33. Implicit Objects • As seen before, some useful variables, like request and session are predefined • These variables are called implicit objects • Implicit objects are defined in the scope of the service method • Can these be used in JSP declarations? • Implicit objects are part of the JSP specifications

  34. The objects request and response • request and responseare the HttpServletRequestand HttpServletResponse arguments of the service method • Using these objects, you can: • Read request parameters • Set response headers • etc. (everything we learned in Servlet lectures)

  35. The object out • This is the Writerused to add write output into the response body • This object implements the interface JspWriter that combines the functionality of PrintWriter and BufferedWriter • Recall that you can adjust the buffer size, or turn buffering off, through use of the buffer attribute of the page directive

  36. The object pageContext • pageContext is a new object introduced by JSP • This object stores all important elements used by the generated Servlet, like the application context, the session, the output writer, etc. • It enable vendors to elegantly extend their JSP implementation • This object is also used to store page-scoped attributes (e.g., Java Beans - discussed later)

  37. The object session • This is the HttpSession object associated with the request • If the session attribute in the page directive is turned off (<%@ page session="false" %>) then this object is not available • Recall that a session is created by default

  38. The object config • This is the ServletConfigof the page, as received in the init() method • Remember: contains Servlet specific initialization parameters • Later, we will study how initialization parameters are passed to JSP pages • Recall that you can also obtain the ServletContextfrom config

  39. The object application • This is the ServletContext as obtained via getServletConfig().getContext() • Remember: • The ServletContext is shared by all Web-application Servlets (including ones generated from JSP) • Getting and setting attributes is with getAttribute and setAttribute of ServletContext • You can use this object to get application-wide initialization parameters

  40. Page Scope • service() local variables • pageContextattributes

  41. Request Scope • request attributes

  42. Session Scope • session attributes

  43. Servlet Scope • Servlet members

  44. Application Scope • application attributes

  45. Servlet Package and Helper Classes • The generated Servlet has a named package • In Tomcat, this package is: org.apache.jsp • In Java, you cannot use classes from the default package (i.e. with no package declaration) from a named package! • Therefore, helper classes used by JSP pages must have a named package

  46. JSP and XML

  47. Simple XML Production <?xml version="1.0"?> <!DOCTYPE colors SYSTEM "colors.dtd"> <?xml-stylesheet type="text/xsl" href="colors.xsl"?> <%! staticString[] colors = {"red","blue","green"}; %> <%@ page contentType="text/xml"%> <colors> <%for(int i=0; i<3; ++i) { %> <color id="<%=i%>"><%= colors[i] %></color> <% } %> </colors>

  48. Generated XML <?xml version="1.0"?> <!DOCTYPE colors SYSTEM"colors.dtd"> <?xml-stylesheet type="text/xsl"href="colors.xsl"?> <colors> <color id="0">red </color> <color id="1">blue</color> <color id="2">green</color> </colors>

  49. JSPX Files • JSPX files are JSP files that have the extension jspx and have XML syntax • Non-XML symbols <%, <%@, etc. are replaced with special JSP tags • Default content type of JSPX is text/xml (and not text/html) • Thus, JSPX files generate XML and can be edited using XML tools

  50. <jsp:expression> Expression </jsp:expression> <%=Expression%> <jsp:scriptlet> Code </jsp:scriptlet> <% Code %> <jsp:declaration> Declaration </jsp:declaration> <%! Declaration %> <jsp:directive.type Attribute="value"/> <%@ Directive %>

More Related