3 jsp design&architecture

8/14/2019 3 JSP Design&Architecture

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JSP Design/Architecture


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Advantage of Front Controller Pattern7Identifying the Operation to Perform6

How to make all the request go to one servlet ?5

JSP Model 2- Front Controller Pattern4

Page-View with bean3

Page-View2

JSP Model 11

contents


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Know

The JSP Model 1 & Model 2 architectures


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Be able to

Implement JSPs using the Model 1 and Model 2approaches


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JSP Model 1 Requests are made directly to the JSP

page or servlets that produce the

response.

JSP or servlet access the enterprise

resources through a java bean andgenerate response themselves.

Two variants:

Page-View

Page-View with bean


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JSP Model 1 Advantage:

simple to program and allows page author to

generate content easily, based upon the

request and the state of the resources.

Disadvantage: the page complexity increases with the

increase of application complexity excessive

java code embedded within JSP page.


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Page-View

JSP Business Processing

All the business processing is done in the jsp


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Page-View with bean

Bean functionality can be modified without

affecting jsp code. Some JSP code will sometimes have tomanipulate sessions ,application-wide resourceor state before response can be generated. This

will lead to more of java code embedded in theJSP code.

Also the flow of the application logic isembedded in the JSP.

JSP Business ProcessingWorker Bean


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JSP Model 2- Front Controller Pattern

Underlying idea of MVC architecture


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Controller

View

View

request

request

response

response

Model

Model

Model 2 Architecture/ Front Controller Pattern

Single control point for presentation tier


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Having one servlet as a single point of entry intowhole application

This entry point produces no output by itself but processes the request

optionally manipulates session andapplication state

redirects requests to appropriate JSP view ora sub-controller that knows how to handle asubset of requests to the application.

Models are provided by java beans created ormanaged by the controller and made availableto JSP views

Preferred approach.


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How to make all the requests go to one

servlet ?

Make url pattern for the servlet as:/*

Problem with this is that when the servlet tries toforward to another url then the request again goes

back to the same servlet Make url pattern for the servlet as:

*.xxx

provided we dont have any such pages in ourapplication with that extension.

For instance we could have pattern as*.html


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In that case, we make all the view pages

as jsp pages so that servlet can forward tojsp pages.

Implies that all the url links that we

make in our HTML pages will link toanother html page even though wedont have even a single html page inour application.


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Identifying the Operation to Perform

Indicate the operation in a hidden formfield, which a POST operation delivers to

the controller; for example:

Indicate the operation in a HTTP GET

query string parameter; for example:

http://myHost/myApp/servlets/myServlet?op=

createUser


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Through requested url paths : Servlet canextract the requested operation's name from

the request URL. Servlet myServlet canextract the requested operation's name fromthe request URL.

String path=request.getServletPath();The BluePrints recommendation is to use

servlet mappings when they are available.Servlet mappings provide the most flexible

way to control where to route URLs based onpatterns in the URL


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Servletrequests

Sub-Controller Class 1 Sub-Controller Class 2

RequestHandlerString handleRequest(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException

returnsURL

Model Class 1 Model Class 2JSP Page 1JSP Page 2

handleRequest()

url

data


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Servlet_C

equestEmp_C Dept_C

RequestHandlerString handleRequest(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException

returnsURL

Employee DepartmentEmpInsertDeptInsert

handleRequest()

url

data

Example


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public class ControllerServlet extends HttpServlet {

public void doGet(HttpServletRequest request,

HttpServletResponse response)throws IOException,ServletException {

String path=request.getServletPath();

RequestHandler rh;

if(path.equals(\empIns.html)){

rh=(RequestHandler) new Emp_C;

else

if(path.equals(\deptIns.html)){

rh=(RequestHandler) new Dept_C;

String view=rh.handleRequest(request,response);

request.getRequestDispatcher(view).forward(request,respons

e);}


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Employee

-empno-empName-dept

boolean insert()static EmployeefindByName(String name)static EmployeefindById(String id)static Vector findAll()

Model classes

Index

view classes

InsertEmployee

FindEmployeeFindDepartme

nt

InsertDepartme

nt

Department

-deptName-managerid

boolean insert()static Vector findAll()static DepartmentfindDept(String dept)


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Controller classes

EmpHandler

Vector findAllDepartments()EmployeefindEmployees(Stringname,String empno)booleaninsertEmployee(String

name,String empno, Stringdept)boolean validateEmployee()

ControllerServlet

doGet()

DeptHandler

Department findDept(Stringname )boolean insertDept(Stringdeptname,String managerid)boolean validateDept()Vector findAllEmployees()

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A Model 1 architecture is best

when the page navigation is simple and fixed, andwhen a simple directory structure can representthe structure of the pages in the application.

Over time, as the application grows and changes,page flow logic accumulates. T

The application becomes difficult to maintainbecause the page flow logic is distributed acrossmultiple pages. This causes maintenanceproblem. All the flow is handled by a single servlet.

Pattern

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Servlet code and the controller code is decoupledfrom sub-controller so any change in one does noteffect another.

The same set of classes (sub-controller and entityclasses) and can be used for a different types ofclient.

Pattern

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