UML Weekend Crash Course™ - To Parent Directory

Session 28—Analysis and Architectural Design of a Web Application 293
servlet turned inside out; instead of having HTML in your Java, you have Java in your
HTML. So simply switching from servlets to JSPs isn’t enough to successfully separate your
HTML view from your Java model and controller. Thus, there must be another way to get the
Java code out of the JSP pages.
A simple solution to this problem would be to move any large chunks of Java code from
your JSP page into regular Java classes and have your JSP page contain method calls to the
methods in those classes. This would remove a very large quantity of Java code from the
JSP, but the JSP page would still have Java syntax method calls in it. JavaBeans represent a
refinement of this solution. For this purpose, a JavaBean is just a regular Java class with
private attributes and public get/set methods for accessing the attributes. Figure 28-4
shows a UML Class diagram of a simple JavaBean for tracking a customer order. Creating a
JavaBean is as simple as it sounds; with proper encapsulation, you will probably meet the
requirements of JavaBeans without even trying.
OrderBean
- item: String
- quantity: int
- costPerItem: double
+ setItem (i: String): void
+ getItem (): String
+ setQuantity (q : int): void
+ getQuantity () : int
+ setCostPerItem (c : double) : void
+ getCostPerItem () : double
+ getTotalCost () : double
+ submitOrder () : boolean
Figure 28-4 UML Class diagram, JavaBean
JSP has special markup tags that can be used to call the get and set methods of the
JavaBean. Thus, the Java syntax method calls can be replaced with markup tags. For example,
the Java syntax and the JSP tag syntax shown here are equivalent method calls, but it
may be easier for a content developer to use the JSP tag syntax.
Java Syntax:
JSP Tag Syntax:
Typically, the code that you move from the JSP pages into JavaBeans will include your
application data, database access code, and business services. What is left in your JSP is
largely the Web content, which is the view of that data. Thus, by using JavaBeans, you can
separate your view from your model and take the first step towards an MVC Web architecture.
Note
This section addresses JavaBeans, not Enterprise JavaBeans (EJB). EJB is a
far-more-involved technology and is beyond the scope of this book.