J2EE Design Patterns

1.1 J2EE Design Patterns

J2EE [java 2 Enterprise Edition] design patterns are the good practices to solve some common recurring coding problems. J2EE Design Patterns is use to develop a good web architecture and application which are flexible and easy to maintain. Applying design patterns implies fast development.
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1.2 Presentation Layer

Presentation layer consist of only view part that is look and feel of the webpages. This layer uses jsp, servlet, html, css, j.s, jquery etc. technologies which are use for developing webpage designing.
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Intercepting Filter use as a pluggable filter to pre and post process requests and responses. A filter manager combines loosely coupled filters in a chain, delegating control to the appropriate filter. In this way, you can add, remove, and combine these filters in various ways without changing existing code.
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Front controller is used when some processing is required before showing the view to user i.e controller runs first. Front controller is mainly a servlet which take the request from client (web browser) and pass it to the model, model do some calculation and send it to controller and then controller send it to view.
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Composite view design pattern is used when multiple subviews are directly embedded to make a single view or layout or template.
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1.2.4 View Helper
As a good programmer your core responsibility is to segregate all the code in different layers and follow DRY and SRP principals i.e view should be used only for designing and formatting porpose in jsp files and other data processing/calculation code should be kept in other classes or layer which will help in maintenance and it also increase code reusability .
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As a good programmer your core responsibility is to segregate all the code in different layers and follow DRY and SRP principals i.e view should be used only for designing and formatting porpose in jsp files and other data processing/calculation code should be kept in other classes or layer which will help in maintenance and it also increase code reusability .
Learn More ...
As a good programmer your core responsibility is to segregate all the code in different layers and follow DRY and SRP principals i.e view should be used only for designing and formatting porpose in jsp files and other data processing/calculation code should be kept in other classes or layer which will help in maintenance and it also increase code reusability .
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1.3 Business Layer

Business layer consist of Business Logic i.e all data processing calculation done here ,this layer is abstract for the client. It process the data coming from view and send it back.
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View delegates logic processing responsibility to business delegate or business object. You want to minimize coupling between clients and the business services, thus hiding the underlying implementation details of the service .
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The service locator design pattern is used when you to implement and encapsulate service and component lookup. Service Locator pattern makes use of caching technique. For the first time a service is required, Service Locator looks up in JNDI and caches the service object.
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Use a session bean as a facade to encapsulate the complexity of interactions between the business objects participating in a workflow. The Session Facade manages the business objects, and provides a uniform coarse-grained service access layer to clients.
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Transfer Object design pattern is use to encapsulate the business data. A single method call is used to send and retrieve the Transfer Object.
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The Transfer Object Assembler combines multiple Transfer Objects from various business components and services, and returns it to the client.
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Use Composite Entity to model, represent, and manage a set of interrelated persistent objects rather than representing them as individual fine-grained entity beans. Composite Entity use to implement persistent Business Objects using local entity beans and POJOs.
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Value list handler is use to cache the results and allow client to search, traverse and select items from the results. The ValueListHandler directly accesses a DAO [Data Access Object] that can execute the required query.
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1.4 Integration Layer

Integration layer hides and encapsulates the business complexities for the clients.Integration layer consist several design patterns are as under
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Service activator design pattern is use to receive asynchronous requests and invoke one or more business services.
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Use a Data Access Object (DAO) to abstract and encapsulate all access to the data source. The DAO manages the connection with the data source to obtain and store data.
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