Service to Worker and Dispatcher View

Avijeet Dash and Satyabrata

Dash

The problems solved by Front Controller and View Helper patterns in

presentation layers is to provide centralized components for managing access

control, content retrieval, view management. These patterns also provide a clear

separation of role among the different layers.

Service to worker and Dispatcher View are patterns, which are combination of

Front Controller and view Helper patterns with a dispatcher component. Though

the structure of the two patterns is more or less same, they are different in

usage of the patterns.

The basic difference lies in the fact that Service to worker promotes more

"up front" work by the controller and dispatcher for authentication,

authorization, content retrieval, validation, view management and navigation. On

the other hand Dispatcher View have relatively lightweight controller and

dispatcher with minimal functionality and most of the functionality is done by

the view it self.

The controller and dispatcher typically play a moderate to large role in

Service to worker. And in Dispatcher View controller and dispatcher play a

limited to moderate role.

The functionality of view management, which is to decide which view to choose

next can be simplified by passing in the next-view information in the request

itself. For an example, click

http://some.server.com/servlet/Controller?next=login.jsp

or

http://some.server.com/servlet/Controller?action=login

In such cases the dispatcher functionality is fairly minimal of simply

forwarding the request and response to the next view using RequestDispatcher.

Dispatcher may use a XML file to map the action element to a JSP file. The

container itself mostly provides this functionality. Dispatcher view may use

such a simple dispatcher as a function in controller or a separate component.

The dispatcher in the service to worker is more sophisticated and may use

business service to decide the next view.

The controller in Service To worker has all the responsibilities of system

services as well as using the helper for talking to business service to get the

display content.

The controller in Dispatcher View may have minimal services of system

services but doesn’t do any content retrieval, which is done by the view

itself. If the system services are minimal, the controller and dispatcher

components can be completely removed and the request can be directly go to the

view.

See the sequence diagrams to see how the components interact in the two

patterns.

Click to view

Service to worker

sequence diagram

Dispatcher view sequence diagram

Sample Code



View in Service to Worker

The AccountVO is the Value Object or Bean Value, which is created by the

command by using a helper. The value object is set to the request object, which

is used by the view for display.

     class="corepatterns.util.AccountVO"

/>

Account Detail for

    name="account"
property="owner" />

View in Dispatcher view

Here the view uses a jsp tag to extract the value object.

Example 7.35 View Ð accountdetails.jsp

<%@ taglib uri="/web-INF/corepatternstaglibrary.tld"



    prefix="corepatterns"

%>

    queryParams="custid,acctkey"

scope="request" />

Account Detail for

    attribute="owner"

/>

    Account

Number :

    attribute="number" />

   

    Account

Type:

    attribute="type" />