数据访问对象设计模式

与数据源特性相关的数据访问代码，往往将数据访问逻辑和业务逻辑捆绑在一起。这使替换或更改程序的数据源变得十分困难，降低程序的扩展性和移植性，同时增加了维护成本。本文详细介绍了数据访问对象设计模式：将数据源的客户访问接口和数据访问机制分离开，使特定的数据源访问AH转化成普通的客户端接口。这样数据访问机制的代码便可根据数据源的变化单独更改，系统的扩展性获得极大提升，维护亦更加容易。依据数据访问对象设计模式来设计系统能很好地解决大型J2EE应用系统设计中遇到的扩展性、维护性等问题。

Data Access Object Pattern

Code that depends on specific features of data resources ties together business logic with data access logic.This makes it difficult to replace or modify an application's data resources,reduces the system's expansibility and increases maintenance cost.The Data Access Object (or DAO) pattern separates a data resource's client interface from its data access mechanisms,adapts a specific data resource's access API to a generic client interface.It allows data access mechanisms to change independently of the code that uses the data,improves the system's expansibility and maintainability.Thus the DAO can be used to solve the expansibility and maintainability problems which are met in most complex J2EE Application.