This chapter is from the book
This chapter is from the book
This chapter is from the book
A Typical Scenario
The diagram in Figure 22.2 shows a typical scenario for a web-based Java system using a database. The web server gathers input data from the user and hands it to the Controller on the upper left. The Controller packages that data into a plain old Java object and passes this object through the InputBoundary to the UseCaseInteractor. The UseCaseInteractor interprets that data and uses it to control the dance of the Entities. It also uses the DataAccessInterface to bring the data used by those Entities into memory from the Database. Upon completion, the UseCaseInteractor gathers data from the Entities and constructs the OutputData as another plain old Java object. The OutputData is then passed through the OutputBoundary interface to the Presenter.
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Figure 22.2 A typical scenario for a web-based Java system utilizing a database
The job of the Presenter is to repackage the OutputData into viewable form as the ViewModel, which is yet another plain old Java object. The ViewModel contains mostly Strings and flags that the View uses to display the data. Whereas the OutputData may contain Date objects, the Presenter will load the ViewModel with corresponding Strings already formatted properly for the user. The same is true of Currency objects or any other business-related data. Button and MenuItem names are placed in the ViewModel, as are flags that tell the View whether those Buttons and MenuItems should be gray.
This leaves the View with almost nothing to do other than to move the data from the ViewModel into the HTML page.
Note the directions of the dependencies. All dependencies cross the boundary lines pointing inward, following the Dependency Rule.