Proxy Design Pattern
The Gang Of Four definition of this design pattern is "Provides a surrogate or placeholder for another object to control access to it". In the example below we use the pattern to enable caching on an ASP.net page. This code uses the Factory design pattern as well.
A VB example of the Proxy Design Pattern
' This code would be run at the web page code behind class
Dim productsProvider As IProducts
Dim cachingEnabled As Boolean = CType(System.Configuration.ConfigurationManager.AppSettings("caching"), Boolean)
productsProvider = ProductsFactory.getProductsProvider(cachingEnabled)
Me.ProductsGrid.DataSource = productsProvider.getProducts()
Me.ProductsGrid.DataBind()
' My Products Interface
Public Interface IProducts
Function getProducts() As StringEnd Interface
' Factory Class to create concrete class
Public
Class ProductsFactory Public Shared Function getProductsProvider(ByVal UseCaching As Boolean) As IProducts
If UseCaching Then
Return New ProxyProducts
Else
Return New Products
End If
End Function
End
Class' The Proxy Products Class
Public Class ProxyProducts
Implements IProducts
Public Function getProducts() As String Implements IProducts.getProducts
' Check if we have the products in cache, if not
' then call the getProducts method from the Products class.
End FunctionEnd Class
' Standard Products Class
Public
Class Products
Implements IProducts
Public Function getProducts() As String Implements IProducts.getProducts
' Query the database for a list of products and return
End Function
End Class
Revision number 1, Wednesday, March 05, 2008 7:56:20 AM by
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