Java E-Commerce Martin Cooke,

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1 Java E-Commerce Martin Cooke, Java technologies for presentation: JSP Today s lecture in the presentation tier Java Server Pages Tomcat examples Presentation How the web tier interacts with the client tier 13/02/2004 Java E-Commerce Martin Cooke, Client browser Client browser Presentation tier Dynamic content webapp Web server Back-end data sources Multiple validation I18N & Browser multiple versions WAP browser Applet (browser component) Standalone client with network connection 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

Java E-Commerce Martin Cooke, 2002 2 Best approach is error prevention: avoid text boxes where possible Lexical Is a single value well-formed? Eg get integer when expected?

2 Java E-Commerce Martin Cooke, Best approach is error prevention: avoid text boxes where possible Lexical Is a single value well-formed? Eg get integer when expected? Easy to do on client side Syntactic Is a composite well-formed? Eg <day>/<month>/<year> Can be done on client Localisation? Semantic Does the input make sense? Eg is it a valid date? Is it a valid credit card number? Frequently can t be done on the client Multiple validation I18N & I18N & Presentation tier is the focus for internationalisation and localisation efforts data in multiple languages Data presentation in multiple locales Good support in Java But not automatic Helps to design in from the start (though rarely done) Client-side + faster response + less network traffic - duplicate logic on multiple clients - can t validate all inputs eg login on client Often done using JavaScript + access to DOM - non-uniform browser support Thick vs thin client applets 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, Stylesheets are the main tool Increased consistency Smaller docs thru reuse Main problem non-uniform support across browsers Related to division don t mix code styles Separation of business and presentation logic Happens via unplanned evolution from small examples Easy to detect and correct with right architecture (next week) Bigger problem Handling dynamic aspects of presentation logic optional dynamic Separation of business and presentation logic Happens via unplanned evolution from small examples Easy to detect and correct with right architecture (next week) Bigger problem Handling dynamic aspects of presentation logic 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

3 Java E-Commerce Martin Cooke, What s wrong with servlets for content generation? Root cause Java Server Pages Servlets acting as HTML outputters can be tedious to write and difficult to maintain. Always a bad idea to have two languages in one file. Servlets require programmers, and programmers make bad graphics designers Difficult to reuse code Too easy to mix presentation and business logic In the dynamic web, its usually the data which changes, not the structure of each page 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, What is JSP? A document-centric approach to dynamic content generation An HTML page with embedded Java JSP Can be used to generate any kind of content dynamically, but most frequently used to generate HTML markup Normally considered as part of the web tier like servlets; strictly speaking, they are (for reasons which will become clear) However, their recommended use is entirely to handle presentational aspects, unlike servlets Claimed benefits of JSP Easier to write than servlets Don t necessarily require programming skills Separate function from form Support code re-use 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

Java E-Commerce Martin Cooke, 2002 4 <HTML> <BODY> <p>today s date is <%= new Date() </p> </BODY> </HTML> Example <HTML> <BODY> <p>today s date is <%= new Date() </p> </BODY> </HTML> Example Normal

4 Java E-Commerce Martin Cooke, <HTML> <BODY> <p>today s date is <%= new Date() </p> </BODY> </HTML> Example <HTML> <BODY> <p>today s date is <%= new Date() </p> </BODY> </HTML> Example Normal HTML page defines structure of document <HTML> <BODY> <p>today s date is <%= new Date() </p> </BODY> </HTML> Example Normal HTML page defines structure of document JSP expression, evaluated when page is requested 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, How it works The ugly truth First-person penalty request for date.jsp date.jsp First time accessing JSP page requires compile Other times, reuse servlet in memory Can avoid first-person penalty by requesting that the page be precompiled Java Compiler response Servlet 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

5 Java E-Commerce Martin Cooke, Shopping form (Tomcat example) Shopping form Shopping form <body bgcolor="white"> <form type=post action=s.jsp> <BR>Please enter item to add or remove:<br> Add Item: <SELECT NAME="item"> <OPTION>Beavis & Butt-head Video collection <OPTION>X-files movie <OPTION>Twin peaks tapes </SELECT> <br> <br> <INPUT TYPE=submit name="submit" value="add"> <INPUT TYPE=submit name="submit" value="remove"> </form> </body> <body bgcolor="white"> <form type=post action=s.jsp> <BR>Please enter item to add or remove:<br> Add Item: <SELECT NAME="item"> <OPTION>Beavis & Butt-head Video collection <OPTION>X-files movie <OPTION>Twin peaks tapes </SELECT> <br> <br> <INPUT TYPE=submit name="submit" value="add"> <INPUT TYPE=submit name="submit" value="remove"> </form> </body> 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, s.jsp <%! private int first = 0; <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke, JSP elements: 3 types <jsp:usebean id="" scope="session" class="sessions.dummycart" " /> <%! private int first = 0; <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke, : Directives <%! private int first = 0; <%@ include file ="s.html" Instructions that control the operation of the JSP translator Happen only once, at translate time 13/02/2004 Java E-Commerce Martin Cooke,

6 Java E-Commerce Martin Cooke, : Actions 3: Scripting elements 3: Scripting elements <jsp:usebean id="" scope="session" class="sessions.dummycart" " /> <%! private int first = 0; Tags that perform document-related tasks such as defining and manipulating session <%@ include file ="s.html" objects via beans (later) 13/02/2004 Java E-Commerce Martin Cooke, <%! private int first = 0; Java Code fragments 3 types: <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke, <%! private int first = 0; Java Code fragments 3 types: declarations use <%!.. <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke, : Scripting elements <%! private int first = 0; Java Code fragments 3 types: declarations expressions use <%=.. execute immediately and write to output <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke, : Scripting elements <%! private int first = 0; Java Code fragments 3 types: declarations expressions scriptlets use <% arbitrary code inserted into translated servlet <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke, Object scopes Objects can be Implicitly through JSP directives Explicitly through actions Directly using scripting code When and where can we use those objects? While scope is clear in Java programs, it is less obvious in JSP, yet is critical 13/02/2004 Java E-Commerce Martin Cooke,

7 Java E-Commerce Martin Cooke, Object scopes Object scopes Object scopes Page Objects may be accessed only within pages where they are Page Request Objects may be accessed only within pages where they are only within pages processing the request in which they were Page Request Session Objects may be accessed only within pages where they are only within pages processing the request in which they were only from pages belonging to the same session as the one in which they were 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, Object scopes Implicit objects Example Page Request Session Application Objects may be accessed only within pages where they are only within pages processing the request in which they were only from pages belonging to the same session as the one in which they were within all pages belonging to the same application Objects that can be used in scriplets and expressions without being explicitly : request The HttpServletRequest object request response The HttpServletResponse object (not much used) page pagecontext The PageContext object page application The ServletContext object application out A JspWriter writing to the output stream page page Synonym for this (not much used) page session The HttpSession object session <% String validated = yes ; session.putvalue( validated, validated); On a different page within the same session: <% String s = (String) session.getvalue( validated ); exception The Throwable object resulting in an error page page 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

8 Java E-Commerce Martin Cooke, Maintaining state JavaBeans reminder JavaBeans reminder Can be done using scriptlets but much better to use JavaBeans <jsp:usebean id="" scope="session" class="sessions.dummycart" /> Initially seen as a building block for visual development environments Nothing more than a class that maintains some data (called properties) and follows certain coding conventions Initially seen as a building block for visual development environments Nothing more than a class that maintains some data (called properties) and follows certain coding conventions Must implement Serializable or Externalizable interface (so that the bean can be saved and retrieved) Must provide a no arguments constructor (so tools and JSP can conveniently instantiate it) Must provide get and set methods for all private properties getpropertyname() or ispropertyname() for boolean props setpropertyname() 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, The simplest possible bean public class mybean implements java.io.serializable { mybean() {} private String myprop = null; public void setmyprop(string s) { myprop = s; } public String getmyprop() { return myprop; } } Accessing and creating beans <jsp:usebean> tries to obtain a reference to an existing bean with the specified id and scope: <jsp:usebean id="" scope="session class="sessions.dummycart" /> If a reference is not found, the bean is newly instantiated Hence the same code can have two different meanings Using beans accessor <jsp:getproperty name="" property= total /> (name here is the id of the usebean directive) mutator <jsp:setproperty name="" property= total value= 0 /> 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

9 Java E-Commerce Martin Cooke, JSP, beans and forms JSP, beans and forms Detailed example - shopping Suppose you have a form with 20 elements. You set up a bean to represent the form s contents (call it myform). You now want to access all those fields for validation etc Suppose you have a form with 20 elements. You set up a bean to represent the form s contents (call it myform). You now want to access all those fields for validation etc <jsp:setproperty name= myform" property= * /> 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, invoked New bean, id= DummyCart.java 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

10 Java E-Commerce Martin Cooke, Cart s instance variables filled in Cart s processrequest method called Cart s processrequest method called item= Beavis & Butt-head Video collection submit= add item= item= item= item= Beavis & Butt-head Video collection submit= add item= 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, Cart s getitems() method Cart s getitems() method Include original form item= item= item= <%! private int first = 0; 13/02/2004 Java E-Commerce Martin Cooke, <%! private int first = 0; 13/02/2004 Java E-Commerce Martin Cooke, <%! private int first = 0; <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke,

11 Java E-Commerce Martin Cooke, Include original form invoked This time, uses existing bean item= <%! private int first = 0; <%@ include file ="s.html" 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke, Exception handling Books Use page directives errorpage attribute: <%@ page iserrorpage= false errorpage= errorhandler.jsp Forwards uncaught exception to error handling page Resources Hunter (2001) Java Servlet Programming (2nd ed) Brown et al (2001) Professional JSP (2nd ed) errorhandler.jsp must flag itself as an error handling page using <%@ page iserrorpage= true 13/02/2004 Java E-Commerce Martin Cooke, /02/2004 Java E-Commerce Martin Cooke,

Islamic University of Gaza Faculty of Engineering Department of Computer Engineering ECOM Advanced Internet Technology Lab.

Islamic University of Gaza Faculty of Engineering Department of Computer Engineering ECOM 5049 Advanced Internet Technology Lab Lab # 10 JAVABEANS IN JSP El-masry May, 2014 Objectives Understanding JavaBeans.