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Chapter 5 Examples
Download the Chapter 5 code View the code examples 5.7 5.8 5.9 5.10 5.11 Example 5.1 Introduce a Controller - JSP Structure<HTML> <BODY> <control:grant_access/> . . . </BODY> </HTML> Example 5.2 Introduce a Controller - Controller Structure
if (grantAccess())
{
dispatchToNextView();
}
else
{
dispatchToAccessDeniedView();
}
Example 5.3 Generate and Store Token
/**
* Save a new transaction token in the
* user's current session, creating
* a new session if necessary.
*
* @param request The servlet request we are processing
*/
protected void saveToken(HttpServletRequest request) {
HttpSession session = request.getSession();
String token = generateToken(request);
if (token != null)
session.setAttribute(TRANSACTION_TOKEN_KEY, token);
}
(Copyright (c) 1999 The Apache Software Foundation. All rights
reserved.)
Example 5.4 Check For a Valid Token
/**
* Return <code>true</code> if there is a transaction
* token stored in the user's current session, and
* the value submitted as a request request parameter
* with this action matches it.
*
* Returns <code>false</code>
* under any of the following circumstances:
* <ul>
* <li>No session associated with this request</li>
* <li>No transaction token saved in the session</li>
* <li>No transaction token included as a request
* parameter</li>
* <li>The included transaction token value does not
* match the transaction token in the user's
* session</li>
* </ul>
*
* @param request The servlet request we are processing
*/
protected boolean isTokenValid(HttpServletRequest request) {
// Retrieve the saved transaction token from our
// session
HttpSession session = request.getSession(false);
if (session == null)
return (false);
String saved = (String)
session.getAttribute(TRANSACTION_TOKEN_KEY);
if (saved == null)
return (false);
// Retrieve the transaction token included in this
// request
String token = (String)
request.getParameter(Constants.TOKEN_KEY);
if (token == null)
return (false);
// Do the values match?
return (saved.equals(token));
}
(Copyright (c) 1999 The Apache Software Foundation. All rights reserved.)
Example 5.5 JSP with Scriptlet Code
<html>
<head><title>Employee List</title></head>
<body>
<%-- Display All employees belonging to a department and earning at
most the given salary --%>
<%
// Get the department for which the employees are
// to be listed
String deptidStr = request.getParameter(
Constants.REQ_DEPTID);
// Get the max salary constraint
String salaryStr = request.getParameter(
Constants.REQ_SALARY);
// validate parameters
// if salary or department not specified, go to
// error page
if ( (deptidStr == null) || (salaryStr == null ) )
{
request.setAttribute(Constants.ATTR_MESSAGE,
"Insufficient query parameters specified" +
"(Department and Salary)");
request.getRequestDispatcher("/error.jsp").
forward(request, response);
}
// convert to numerics
int deptid = 0;
float salary = 0;
try
{
deptid = Integer.parseInt(deptidStr);
salary = Float.parseFloat(salaryStr);
}
catch(NumberFormatException e)
{
request.setAttribute(Constants.ATTR_MESSAGE,
"Invalid Search Values" +
"(department id and salary )");
request.getRequestDispatcher("/error.jsp").
forward(request, response);
}
// check if they within legal limits
if ( salary < 0 )
{
request.setAttribute(Constants.ATTR_MESSAGE,
"Invalid Search Values" +
"(department id and salary )");
request.getRequestDispatcher("/error.jsp").
forward(request, response);
}
%>
<h3><center> List of employees in department #
<%=deptid%> earning at most <%= salary %>. </h3>
<%
Iterator employees = new EmployeeDelegate().
getEmployees(deptid);
%>
<table border="1" >
<tr>
<th> First Name </th>
<th> Last Name </th>
<th> Designation </th>
<th> Employee Id </th>
<th> Tax Deductibles </th>
<th> Performance Remarks </th>
<th> Yearly Salary</th>
</tr>
<%
while ( employees.hasNext() )
{
EmployeeVO employee = (EmployeeVO)
employees.next();
// display only if search criteria is met
if ( employee.getYearlySalary() <= salary )
{
%>
<tr>
<td> <%=employee.getFirstName()%></td>
<td> <%=employee.getLastName()%></td>
<td> <%=employee.getDesignation()%></td>
<td> <%=employee.getId()%></td>
<td> <%=employee.getNoOfDeductibles()%></td>
<td> <%=employee.getPerformanceRemarks()%>
</td>
<td> <%=employee.getYearlySalary()%></td>
</tr>
<%
}
}
%>
</table>
<%@ include file="/jsp/trace.jsp" %>
<P> <B>Business logic and presentation formatting are
intermingled within this JSP view. </B>
</body>
</html>
Example 5.6 JSP with Scriptlet Code Extracted
<%@ taglib uri="/WEB-INF/corepatternstaglibrary.tld"
prefix="corepatterns" %>
<html>
<head><title>Employee List</title></head>
<body>
<corepatterns:employeeAdapter />
<h3><center>List of employees in
<corepatterns:department attribute="id"/>
department - Using Custom Tag Helper Strategy </h3>
<table border="1" >
<tr>
<th> First Name </th>
<th> Last Name </th>
<th> Designation </th>
<th> Employee Id </th>
<th> Tax Deductibles </th>
<th> Performance Remarks </th>
<th> Yearly Salary</th>
</tr>
<corepatterns:employeelist id="employeelist_key">
<tr>
<td><corepatterns:employee
attribute="FirstName"/></td>
<td><corepatterns:employee
attribute="LastName"/></td>
<td><corepatterns:employee
attribute="Designation"/> </td>
<td><corepatterns:employee
attribute="Id"/></td>
<td><corepatterns:employee
attribute="NoOfDeductibles"/></td>
<td><corepatterns:employee
attribute="PerformanceRemarks"/></td>
<td><corepatterns:employee
attribute="YearlySalary"/></td>
<td>
</tr>
</corepatterns:employeelist>
</table>
</body>
</html>
Example 5.7 Tight Coupling between a Domain Object and HttpServletRequest object
/** The following excerpt shows a domain object that
is too tightly coupled with HttpServletRequest **/
public class Customer
{
public Customer ( HttpServletRequest request )
{
firstName = request.getParameter("firstname");
lastName = request.getParameter("lastname ");
}
}
Example 5.8 Reduced Coupling between a Domain Object and HttpServletRequest object
// Domain Object not coupled with HttpServletRequest
public class Customer
{
public Customer ( String first, String last )
{
firstName = first;
lastName = last;
}
}
Example 5.9 Conversion Logic Embedded Within View
<html>
<head><title>Employee List</title></head>
<body>
<h3><head><center> List of employees</h3>
<%
String firstName =
(String)request.getParameter("firstName");
String lastName =
(String)request.getParameter("lastName");
if ( firstName == null )
// if none specific, fetch all
firstName = "";
if ( lastName == null )
lastName = "";
EmployeeDelegate empDelegate = new
EmployeeDelegate();
Iterator employees =
empDelegate.getEmployees(
EmployeeDelegate.ALL_DEPARTMENTS);
%>
<table border="1" >
<tr>
<th> First Name </th>
<th> Last Name </th>
<th> Designation </th>
</tr>
<%
while ( employees.hasNext() )
{
EmployeeVO employee = (EmployeeVO)
employees.next();
if ( employee.getFirstName().
startsWith(firstName) &&
employee.getLastName().
startsWith(lastName) ) {
%>
<tr>
<td><%=employee.getFirstName().toUpperCase() %></td>
<td> <%=employee.getLastName().toUpperCase() %></td>
<td> <%=employee.getDesignation()%></td>
</tr>
<%
}
}
%>
</table>
Example 5.10 Logic Extracted into Helper Classes
<html>
<head><title>Employee List - Refactored </title>
</head>
<body>
<h3> <center>List of employees</h3>
<corepatterns:employeeAdapter />
<table border="1" >
<tr>
<th> First Name </th>
<th> Last Name </th>
<th> Designation </th>
</tr>
<corepatterns:employeelist id="employeelist"
match="FirstName, LastName">
<tr>
<td><corepatterns:employee attribute= "FirstName"
case="Upper" /> </td>
<td><corepatterns:employee attribute= "LastName"
case="Upper" /></td>
<td><corepatterns:employee attribute=
"Designation" /> </td>
<td>
</tr>
</corepatterns:employeelist>
</table>
Example 5.11 Controlling Access Using a Control Component<%@ taglib uri="/WEB-INF/corepatternstaglibrary.tld" prefix="corepatterns" %> <corepatterns:guard/> <html> <head><title>Hide Resource from Client</title></head> <body> <h2>This view is shown to the client only if the control component allows access. The view delegates the control check to the guard tag at the top of the page.</h2> </body> </html> |
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