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Web Application Architecture

Some classic patterns of web applications

These are fairly well documented in some Excellent Books. We recommend that you make yourself familiar with the basic patterns, then follow through by using an existing Java Web Framework. Do NOT attempt to create your own web framework before you really really know what you are doing.

  • MVC

    • Model
    • View
    • Controller - Input Controller

  • Front Controller

    • Command Pattern
    • Intercepting Filters (filter chain)

  • Application Controller

  • Template view

Layers

Web applications tend to follow the pattern of Marinescu layers (with some naming from Fowler):

Presentation Presentation(Application Controller) Service Layer Domain Model Persistence / data source

Maven modules

Maven modules are used to separate according to dependencies. Java packages are used to group according to function (see Structuring packages and contexts).

Essence: Use packages to seperate function. Use modules to seperate layers AND domains.

  • domainImpl, domainAPI
  • repository (API)
  • daoImpl
  • daoMock
  • controller
  • web (web.xml, jsp, js which calls java code)
  • taglib
  • resources (images, html, javascript, css, velocity, freemarker - use filter)
  • jsp-fragments (JSP-files must use war overlay, see Web Application Fragments)

Click the diagram to view full size Maven

Use of Session

Some clear advice

Do not allow the use of the HttpSession to trickle down beyond your web layer (see Structuring packages and contexts).

Some questions you should ask yourself

We advise that the application is architectured with a clear policy on how to manage session. Here are some questions you should consider:

  • where should it be available?
  • what parameters to send in the session
  • session hijacking?
  • Use of cookies.
  • How much state do you allow in the session, and what are the consequences of having too much?
  • How do you manage the session (transparent, actively, do you use a SessionContainer object?)
  • Is it possible to do conversation scoping/bijection?

Use of intermediary objects and form backing objects

What are the ups and downs of using them as opposed to using domain objects directly in the web layer?

Mapping patterns to Struts2 notes

We took a look at some classical patterns from MVC and Fowler..

  • MVC

    • Model - domain
    • View - results (jsp, freemarker) backed by formBean (action)
    • Controller (actions)
      • Input Controller - implemented with Interceptors and/or in Actions

  • Front Controller - FilterDispatcher; configured in struts.xml

    • Web handler
    • Command Pattern
  • Intercepting Filters (filter chain) is called Interceptor stack
  • Application Controller - FilterDispatcher; configured in struts.xml
  • Template view - results

Input controllers and app controlls should be stricly held in the web module/presentation layer.

Features: -navigation -command mapping -result mapping -type conversion

The reason is that they often depend on things that are web-specific (urls, string values, etc).

The Commands are strictly held in the controller module/application layer.

Features on this leve. -validation -execution

Keeping web-awareness out of your controller layer is a Good Thing.