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Jeff Schmitt November 16, 2001

Application Architectures for Interactive Web Applications: Java JSP and Model/View/Controller Techniques. Jeff Schmitt November 16, 2001. ABSTRACT. This talk is the report of my sabbatical leave during Spring 2001 in which I explored some new techniques in using the Java language to

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Jeff Schmitt November 16, 2001

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  1. Application Architectures for Interactive Web Applications: Java JSP and Model/View/ControllerTechniques Jeff Schmitt November 16, 2001

  2. ABSTRACT This talk is the report of my sabbatical leave during Spring 2001 in which I explored some new techniques in using the Java language to develop interactive web applications. Java Server Pages technology (JSP) facilitates the development of interactive websites with dynamically generated content. JSP programs contain ordinary HTML tags mixed with Java code. Custom tag libraries and Template processing are techniques which allow the Java code to be isolated from the HTML. This application architecture is based on the principles of Model/View/Controller.

  3. Web Application Components • Client -- typically a Web Browser • HTTP -- request, response protocol between client and server • HTML files -- static web content • Webserver -- serves HTML files and • looks for certain request patterns, then forwards request to servlet engine, for example: /servlet/* • Servlet Engine -- supports execution of servlets • Servlet -- handles request from client, generates response to client • JSP Engine -- supports the compilation of files into Servlets • Web Application -- a collection of HTML files, Servlets and JSP pages to implement an information system on the web.

  4. Single Tier -- Mainframe Two Tier- Client-Server LAN N-Tier -- Web Application INTERNET Database Server Web Server Application Server Tiered Systems

  5. Servlet Lifecycle service() init() destroy()

  6. request() init() service() Process request response response destroy() Servlet Sequence Diagram Client Webserver Servlet

  7. request request response response Servlet Multithreading Client 1 Servlet Client 2

  8. ServletsAdvantages Disadvantages • Servlet mapping(servlet is not a web page) • Hard for Web Designer to change the HTML part of the code • HTML (presentation) and Java code (business logic) mixed together • Scalable • Persistent • Simple • Flexible • Support • Stable API • Run in separate memory space from Server

  9. XML Notation • Begin and end within same tag:<something/> • Begin and end as two separate tags:<something> … </something> • Document Type Definition<?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN""http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">

  10. JSP -- Java Server Pages • Similar to servlets, but they resemble HTML pages • Placed in web folders mixed with HTML files, acts like an HTML file • Compiled automatically to a servlet when first referenced or when the file is changed by programmer. • Intended to help separate the presentation (HTML response) from the logic (processing logic). • Similar to Microsoft's Application Server Pages (ASP)

  11. request request JSP to Servlet Compile Servlet servlet init() service() Process request response response JSP Lifecycle Client Webserver Servlet JSP

  12. JSP scripting elements • JSP Comments<%-- jsp comment --%> • Declarations: placed in static part of servlet<%! String filePath="/users";%> • Expressions: evaluate to a string<%= request.getParameter("NAME")%> • Scriptlets: any Java statements<% (java statements) %> • Template Text: inserted into response<TABLE BORDER=1><TR><TH>Name:<TD><INPUT NAME="NAME" size=50 MAXLENGTH=50>

  13. JSP Default Objects

  14. JSP Object Scope

  15. Custom JSP tags • Assemble reusable JSP code for easy use • An XML-like front end to access Java programming • Designed to bridge the intersection between java programmers and web designers • Tag library holds definitions of custom tags<%@ taglib uri="jakarta-taglib/dbtags" prefix="sql" %> • Custom tags save in Tag Library File .tld • Many useful Tag Libraries exist for the common tasks such as database access, email, file access

  16. DBTags • From Apache Jakarta project • Allow use of JDBC with Java details hidden • Easy to use • Invisible exception handling

  17. <sql:connection> • establish connection to server <%-- open a database connection --%> <sql:connection id="conn1"> <%-- required --%> <sql:url>jdbc:mysql://localhost/test</sql:url> <%-- optional --%> <sql:driver>org.gjt.mm.mysql.Driver</sql:driver> <%-- optional --%> <sql:userId>root</sql:userId> <%-- optional --%> <sql:password>notVerySecure</sql:password> </sql:connection>

  18. Statement and Query • The "escapeSql" tag can be used inside a SQL query to SQL-escape your input values if they contain single quotes. <%-- insert a row into the database --%> <sql:statement id="stmt1" conn="conn1"> <%-- set the SQL query --%> <sql:query> insert into test_books (id, name) values (3, '<sql:escapeSql> <%=request.getParameter("book_title")%></sql:escapeSql>') </sql:query> <%-- execute the query --%> <sql:execute/> </sql:statement>

  19. <sql:resultset> <table> <sql:statement id="stmt1" conn="conn1"> <sql:query> select id, name, description from test_books order by 1 </sql:query> <%-- loop through the rows of your query --%> <sql:resultSet id="rset2"> <tr> <td><sql:getColumn position="1"/></td> <td><sql:getColumn position="2"/></td> <td><sql:getColumn position="3"/> <%-- print out a comment if the book has no description --%> <sql:wasNull>[no description]</sql:wasNull></td> </tr> </sql:resultSet> </sql:statement> </table>

  20. JSP Action Elements • Control Tags for request-time include • Optional parameters for Control tags • Allow JSP programs to implement the Controller aspect of the Model-View-Controller architecture • <jsp:include page="header.jsp"/> • <jsp:forward page="html.jsp/> • <jsp:forward page="html.jsp"> • <jsp:param name="page" value="guestview"/> • </jsp:forward>

  21. request request JSP to Servlet Compile Servlet servlet service() Process request request JSP to Servlet Compile Servlet servlet service() Process request response response JSP Forward Client Webserver Servlet 1 Servlet 2 JSP

  22. Classical Model-View-Controller Architecture Model Queries View Model Change Notification User Events Select a View Model Changes Controller Example: A Clock Application

  23. Problems with JSP • Although intended to help separate the presentation logic (VIEW) from the business logic (MODEL), JSP does not go far enough • JSP programs are often a mix of HTML and business logic, which creates a problem if the design of the page (VIEW) needs to be changed • HTML changes need to be made by web designers who are not necessarily programmers • Solutions to this problem include WebMacro, Struts, FreeMarker, Velocity

  24. FreeMarker Template Processing • Makes substitutions of text in a template based on a set of identifiers in a table ModelRoot) • Works with any form of text files including HTML, XML. and Data files Template Cache ModelRoot Freemarker Resulting web page

  25. FreeMarker Data Structures • SimpleHash -- a random access table of words.Each word is associated with a value which can be any of the three Freemarker structures • SimpleList -- a sequential access list of any of the three Freemarker structures • SimpleScalar -- a String of text ModelRoot -- the root of the structuremust be a SimpleHash

  26. Freemarker RootHash rootHash NAME AFF1 AFF2 EMAIL Joe Towson U guestbook COSC joe@towson NAME AFF1 AFF2 EMAIL NAME AFF1 AFF2 EMAIL

  27. Freemarker Template Scripting • Value Substitution from rootHash${request.NAME} • Freemarker Comments<comment> . . . </comment> • List iteration<loop guestbook as entry> . . . </list> • Conditional<if> . . . <else> . . . </if> • Text inclusion from another template file<include "footer.html">

  28. FreeMarker Template Cache • Manages the folder where templates are stored • Loads and compiles templates into tokenized form for efficiency • Recognizes changes to templates while application is running

  29. guestsign.jsp guestview.jsp html.jsp?page=guestsign html.jsp?page=guestview html.jsp?page=login.jsp delete?id=34 guestview.jsp checklogin.jsp guestview.jsp Guestbook: Java Web Application html.jsp?page=guestbook jsp:forward action or link

  30. Guestbook Demo http://www.mycgiserver.com/~fontanini/introfm/html.jsp?page=guestbook

  31. I18N • Internationalization • Language and Cultural differences • Dates Times • Browser sends header: Accept-language: en-us • First two characters choose template file: • guestbook_en.html • guestbook_it.html • Example: http://www.mycgiserver.com/~fontanini/fm/guestbook.jsp

  32. Conclusion • JSP is Java that looks like HTML • Custom Tags make programming “easy” • Separation of business logic and presentation is desirable for larger “Enterprise” projects • JSP alone does not achieve this separation • EJB, and other technologies are complicated • Template processing provides the desired separation, rather easily and elegantly. • Thank you for attending. Any questions?

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