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15.2 Example: An On Line Travel Agent

tially based upon the action requested. For example, pressing the  Book

Flights  button should show a list of available flights on the dates specified,

ordered by price (see Figure 15 1). The user's real name, frequent flyer infor

mation, and credit card number should be used to generate the page. On the

other hand, selecting  Edit Account  should show any previously entered cus

tomer information, letting the user modify values or add entries. Likewise, the

actions resulting from choosing  Rent Cars  or  Find Hotels  will share much

of the same customer data but will have a totally different presentation.

To accomplish the desired behavior, the front end (Listing 15.2) submits

the request to the top level travel servlet shown in Listing 15.3. This servlet

looks up the customer information (see Listings 15.5 through 15.9), puts it in

the

HttpSession

 object associating the value (of type

coreservlets.Trav

elCustomer

) with the name

customer

, and then forwards the request to a

different JSP page corresponding to each of the possible actions. The desti

nation page (see Listing 15.4 and the result in Figure 15 2) looks up the cus

tomer information by means of

             class="coreservlets.TravelCustomer"

             scope="session" />

then uses

jsp:getProperty

 to insert customer information into various

parts of the page. You should note two things about the

TravelCustomer

class (Listing 15.5).

First, the class spends a considerable amount of effort making the customer

information accessible as plain strings or even HTML formatted strings through

simple properties. Almost every task that requires any substantial amount of

programming at all is spun off into the bean, rather than being performed in the

JSP page itself. This is typical of servlet/JSP integration the use of JSP does not

entirely obviate the need to format data as strings or HTML in Java code. Sig

nificant up front effort to make the data conveniently available to JSP more than

pays for itself when multiple JSP pages access the same type of data.

Second, remember that many servers that automatically reload servlets when

their class files change do not allow bean classes used by JSP to be in

the auto reloading directories. Thus, with the Java Web Server for example,

TravelCustomer

 and its supporting classes must be in

install_dir/

classes/coreservlets/

, not

install_dir/servlets/coreservlets/

Tomcat 3.0 and the JSWDK 1.0.1 do not support auto reloading servlets, so

TravelCustomer

 can be installed in the normal location.

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.

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