Common JEE Application Design Patterns

• Typesafe enum pattern/enum in JDK 1.5+
• code to an interface not an implementation
• abstract parent class to promote reuse for subclasses
• factory method pattern (loose couples calling code from instances created)
• abstract factory pattern  (specific method for each concrete type)
• builder pattern (similar to factory except user had more flexibility (builder.add(x), builder.add(y), etc.)
• strategy pattern (strategy encapsulates algorithms not data)
• decorator design pattern: (implements same interface as object it decorates)
• visitor pattern: (avoids lots of typecasts and instanceof to do common method on different types)
• iterator pattern
• template method pattern (e.g. Spring JDBC and Spring JMS)
• composite design pattern: (act on Manager or Staff object in same way. both subs of employee)
• facade pattern: (interface to large set of classes)
• observer pattern: (observer registers with publisher, publisher notifies observer of event)
• command pattern: OO equivalent of callbacks (sender object invokes operation, receiver object  receives request to execute certain operation)
• proxy pattern: (remote: EJB, RMI, CORBA, virtual: create memory intensive object on demand (lazy load hibernate objects when needed), access: different clients get different access rights)
• dynamic proxy: (reflection based; come at a performance cost; common in AOP)
• adapter pattern (wrap API)
• service activator pattern (ala MessageBean)  services need a way to be activated asynchronously
• For completion: (bridge, chain of responsibility)
• For completion JEE (MVC, front controller, composite view, view helper, dispatcher view, service to worker, business delegate, session facade, value object, fast lane reader, service locator)

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