Design and implementation of data access layer based on design pattern

The web system exists different data sources to access, and each data source has specific access ways. According to design patterns and Open-Closed Principle, data access layer is designed that connects business layer to access data layer. The data access layer is realized by factory method and reflection mechanism. In the factory method, reflection mechanism is used to read key-value pairs of the configuration file, and data access class instance is dynamically generated so that the system has a better general performance, scalability and maintainability.