Enterprise
Java
Model, View, Controller
Web Architecture
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First, there were servlets
•
•
•
•
Enterprise
Java
And things were good
Faster than CGI programs
More scalable with built-in threading capability
Value-added features
– Request/Response, Sessions
• Full Java API access
– JDBC, JMS, EJB, JavaMail, etc.
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Hmm, maybe not so good
Enterprise
Java
• out.printlns in the code became tedious
• Takes a programmer to write HTML pages
– Skill mismatch
• No automated tool support
• Mechanisms developed to output HTML pages
– Inclusion of pages
– htmlKona
– Element Construction Set (ECS)
• There has to be a better way
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Then there were JSPs
Enterprise
Java
• Page-centric view of the world
• Limited programmer involvement
• JSPs became ubiquitous for dynamic HTML page
generation
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Model 1 Architecture
Java Bean
Browser
JSP
Enterprise
Java
EJB
Database
Custom
Tags
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Model 1 Architecture
Enterprise
Java
• JSP-centric
• Suitable for small systems
• Susceptible to abuse
– Excessive Java code in JSPs
– Flow control issues
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Hybrid Approach
Enterprise
Java
• Use servlets for flow-control; JSPs for HTML pages with
dynamic content
• Allows programmer/web designer specialization
• Hybrid Approach=Model 2 Architecture
• A.K.A. MVC
– Controller=Servlet+Helper Classes
– Model=Application Data/Operations
– View=Output Rendered for User
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Model 2 Architecture
Enterprise
Java
2
EJB
Servlet
3
1
Browser
4
Java Bean
Database
5
6
JSP
Custom
Tags
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Model 2 Benefits
Enterprise
Java
• Allows programmer to implement flow control, system
operations in Java/Servlets
• Allows web page designers to develop HTML/JSP pages
– Automated tool support
• Higher degree of re-use; more maintainable architecture
for larger systems
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Struts
Enterprise
Java
• ‘Standard’ MVC framework
• Struts 1.0 released in January 2001
• MVC architecture with support for:
–
–
–
–
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Configurable site navigation
Form handling
Internationalization
Extensive Custom tag libraries
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Enterprise
Java
Struts Architecture
Action
Mappings
2
Browser
8
1
3
ActionServlet
Database
Action
4
Bean
6
5
7
View
(Servlet/JSP/HTML)
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Struts Application Flow
Enterprise
Java
• All requests are first processed by the action servlet
• Refers to ActionMappings to determine action to invoke
– Calls Actions you’ve implemented for your application
– Should be adapters to the rest of the application
• Action returns view to forward to
• View renders data placed in request or session scope by Action class
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A corej2ee MVC-light
Enterprise
Java
• Struts and similar solutions provide for robust solutions
– should be considered for most real implementations
– Too little time to cover the details in this course
• Introduce MVC using a smaller-scale implementation
– based on same similar MVC concepts
– functional, but does not cover full array of issues involved in a
Web-based development
• its simplicity makes understanding the MVC components possible
within the scope of this course
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corej2ee.web Interfaces/Classes
HttpServlet
Controller
+PRINT_DEBUG:boolean
+DEBUG_PREFIX:String
+NAVIGATION_CLASS:String
+UNKNOWN_URI:String
+EVENT_CONTEXT:String
+EVENT:String
-navigation_:Navigation
-unknownUri_:String
+init:void
+doGet:void
+doPost:void
#debug:void
servletInfo:String
interface
interface
interface
Navigation
Route
Worker
+getRoute:Route
+getNextPage:String
worker:Worker
+SUCCESS:String
+ERROR:String
+RESULT:String
+ERROR_MESSAGE:String
+execute:Object
EnvEntryNavigator
+PRINT_DEBUG:boolean
+DEBUG_PREFIX:String
+ROUTE_CONTEXT:String
#routes_:Map
+EnvEntryNavigator
+init:void
+getRoute:Route
#buildRoute:Route
+toString:String
#debug:void
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Java
MVC
BasicRoute
-worker_:Worker
-successUri_:String
-failUri_:String
+BasicRoute
+getNextPage:String
+toString:String
NullWorker
+execute:Object
worker:Worker
14
corej2ee.web.Controller
Enterprise
Java
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException{
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String path=request.getServletPath();
try {
Route route = navigation_.getRoute(path);
String uri = unknownUri_;
if (route != null) {
Worker worker = route.getWorker();
Object result = worker.execute(
getServletContext(),request,response);
uri = route.getNextPage(result);
}
RequestDispatcher rd = getServletContext().getRequestDispatcher(uri);
if (rd != null) {
rd.forward(request, response);
}
else {
response.sendError(HttpServletResponse.SC_NOT_FOUND,
"unable to locate uri '" + uri
+ "' while handling path '" + path
+ "'");
}
}
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corej2ee.web.EnvEntryNavigator
web.xml Configuration
Enterprise
Java
<!-- begin: listPrincipals 1 -->
<env-entry>
<env-entry-name>route/content-listPrincipals1/worker</env-entry-name>
<env-entry-value>corej2ee.examples.principal.web.GetPrincipalsDAOWorker
</env-entry-value>
<env-entry-type>java.lang.String</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>route/content-listPrincipals1/success</env-entry-name>
<env-entry-value>/WEB-INF/content/showResult.jsp</env-entry-value>
<env-entry-type>java.lang.String</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>route/content-listPrincipals1/fail</env-entry-name>
<env-entry-value>/WEB-INF/content/ErrorPage.jsp</env-entry-value>
<env-entry-type>java.lang.String</env-entry-type>
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corej2ee.web.EnvEntryNavigator
web.xml Configuration
Enterprise
Java
<!-- begin: listPrincipals 2 -->
<env-entry>
<env-entry-name>route/content-listPrincipals2/worker</env-entry-name>
<env-entry-value>corej2ee.examples.principal.web.GetPrincipalsDAOWorker
</env-entry-value>
<env-entry-type>java.lang.String</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>route/content-listPrincipals2/success</env-entry-name>
<env-entry-value>/WEB-INF/content/printPrincipals.jsp</env-entry-value>
<env-entry-type>java.lang.String</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>route/content-listPrincipals2/fail</env-entry-name>
<env-entry-value>/WEB-INF/content/ErrorPage.jsp</env-entry-value>
<env-entry-type>java.lang.String</env-entry-type>
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corej2ee.examples.principal.web
Workers
Worker
PrincipalDAOWorker
+PRINT_DEBUG:boolean
+DEBUG_PREFIX:String
-DB_NAME:String
connectionBean_:ConnectionBean
principalDAO_:PrincipalDAO
+PrincipalDAOWorker
#closeConnection:void
#getPrincipalType:String
#getPrincipal:Principal
#log:void
Enterprise
Java
interface
corej2ee.web.Worker
+SUCCESS:String
+ERROR:String
+RESULT:String
+ERROR_MESSAGE:String
+execute:Object
connection:Connection
DAO:PrincipalDAO
GetPrincipalsDAOWorker GetPrincipalDAOWorker InsertPrincipalDAOWorkerModifyPrincipalDAOWorker
+GetPrincipalsDAOWorker +GetPrincipalDAOWorker +InsertPrincipalDAOWorker +ModifyPrincipalDAOWorker
+execute:Object
+execute:Object
+execute:Object
+execute:Object
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corej2ee.examples.principal.web.
GetPrincipalsDAOWorker
Enterprise
Java
public Object execute(ServletContext context,
HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
Connection conn = null;
try {
conn = getConnection();
Collection principals = getDAO().findByWhere(conn, "1=1");
request.setAttribute(RESULT, principals);
return SUCCESS;
}
catch (Exception ex) {
request.setAttribute(ERROR_MESSAGE, ex.toString());
return ERROR;
}
finally {
closeConnection(conn);
}
}
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principalWEB showResult.jsp
Enterprise
Java
<jsp:directive.page errorPage="/ExceptionPage.jsp" />
<jsp:directive.page import="corej2ee.web.*" />
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<head>
<title>Show Result</title>
</head>
<body>
<center><h1>Results</h1></center>
<%=request.getAttribute(Worker.RESULT)%>
</body>
</html>
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principalWEB showResult.jsp
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Java
21
principalWEB printPrincipals.jsp
<jsp:directive.page errorPage="/ExceptionPage.jsp" />
<jsp:directive.page import="corej2ee.examples.principal.*" />
<jsp:directive.page import="corej2ee.web.*" />
<html>
<head>
<title>List Principals</title>
</head>
<body>
<center><h1>Principals</h1></center>
<nl>
<jsp:scriptlet>
Collection principals = (Collection)request.getAttribute(Worker.RESULT);
for(Iterator itr=principals.iterator(); itr.hasNext(); ) {
</jsp:scriptlet>
<li><jsp:expression>itr.next()</jsp:expression></li>
<jsp:scriptlet>
}
</jsp:scriptlet>
</nl>
</body>
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MVC
Enterprise
Java
22
principalWEB printPrincipals.jsp
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Java
23
Resources
Enterprise
Java
• http://jakarta.apache.org/struts/
• http://jguru.com/faq/Struts
• http://jguru.com/forums/home.jsp?topic=Struts
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