论数据访问层设计技术及其应用
在信息系统的开发与建设中，分层设计是一种常见的架构设计方法，区分层次的目的是为了实现“高内聚低耦合”的思想。分层设计能有效简化系统复杂性，使设计结构清晰，便于提高复用能力和产品维护能力。一种常见的层次划分模型是将信息系统分为表现层、业务逻辑层和数据访问层。信息系统一般以数据为中心，数据访问层的设计是系统设计中的重要内容。数据访问层需要针对需求，提供对数据源读写的访问接口；在保障性能的前提下，数据访问层应具有良好的封装性、可移植性，以及数据库无关性。
请围绕“论数据访问层设计技术及其应用”论题，依次从以下三个方面进行论述。
1．概要叙述你参与管理和开发的与数据访问层设计有关的软件项目，以及你在其中所担任的主要工作。
2．详细论述常见的数据访问层设计技术及其所包含的主要内容。
3．结合你参与管理和开发的实际项目，具体说明采用了哪种数据访问层设计技术，并叙述具体实施过程以及应用效果。
正确答案及解析
正确答案
解析
一、首先用400-600字的篇幅简要叙述作者参与开发的软件系统的概要和所担任的工作。
二、数据访问层的技术主要在于数据映射的问题如写Hibernate或iBATIS的应用。
Hibernate是一个开放源代码的对象关系映射框架，它对JDBC进行了非常轻量级的对象封装，它将POJO与数据库表建立映射关系，是一个全自动的orm框架，hibernate可以自动生成SQL语句，自动执行，使得Java程序员可以随心所欲的使用对象编程思维来操纵数据库。 Hibernate可以应用在任何使用JDBC的场合，既可以在Java的客户端程序使用，也可以在Servlet/JSP的Web应用中使用，最具革命意义的是，Hibernate可以在应用EJB的J2EE架构中取代CMP，完成数据持久化的重任。
iBATIS一词来源于“internet”和“abatis”的组合，是一个由Clinton Begin在2002年发起的开放源代码项目。于2010年6月16号被谷歌托管，改名为MyBatis。是一个基于SQL映射支持Java和.NET的持久层框架。
三、详细论述你在项目中运用相关技术进行开发的，此时无非就是如何用好这些技术。
Hibernate的调优方案：
制定合理的缓存策略；
尽量使用延迟加载特性；
采用合理的Session管理机制；
使用批量抓取，设定合理的批处理参数（batch_size）；
进行合理的O/R映射设计。
Mybatis调优方案：
MyBatis在Session方面和Hibernate的Session生命周期是一致的，同样需要合理的Session管理机制。MyBatis同样具有二级缓存机制。 MyBatis可以进行详细的SQL优化设计。
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