技术已经越来越多地应用到大型网络系统开发中，本文中，笔者将介绍EJB（Enterprise Java Beans）的定义、基于EJB技术的应用系统结构模型以及EJB组件的内容和分类，最后结合基于EJB的结构模型和EJB组件开发了一个商务预订系统。 EJB从技术上而言不是一种“产品”，而是一种技术规范。SUN公司对EJB的定义是：EJB的结构是开发和配置基于组件的分布式商务应用程序的一种组件结构。用EJB结构开发的应用程序是可伸缩的、事务型的、多用户安全的。这些应用程序可能只需编写一次，却可以在支持EJB规范的任务服务器平台上进行配置。总的来说，EJB是一个组件事务监控的标准服务器端的组件模型。 基于EJB技术的系统结构模型 EJB结构是一个服务端组件结构，是一个层次性结构，其结构模型如图1所示。该结构模型在通常情况下可分为客户层、业务逻辑层和数据层，下面笔者对此作一简单介绍。 [img]http://www.okasp.com/images/tech/20011114_01.jpg> %E5%9B%BE1%EF%BC%9A%E5%9F%BA%E4%BA%8EEJB%E7%9A%84%E5%BA%94%E7%94%A8%E7%BB%93%E6%9E%84%E6%A8%A1%E5%9E%8B %E5%AE%A2%E6%88%B7%E5%B1%82 %E4%B8%BB%E8%A6%81%E6%98%AF%E7%94%A8%E6%9D%A5%E6%BB%A1%E8%B6%B3%E5%AF%B9%E6%95%B4%E4%B8%AA%E7%B3%BB%E7%BB%9F%E7%9A%84%E5%90%84%E7%A7%8D%E8%AE%BF%E9%97%AE%E9%9C%80%E6%B1%82%E5%B9%B6%E5%A4%84%E7%90%86%E4%BB%A5%E4%B8%8B%E5%B7%A5%E4%BD%9C%EF%BC%9A %E6%8E%A5%E6%94%B6%E7%94%A8%E6%88%B7%E7%9A%84%E8%BE%93%E5%85%A5%EF%BC%8C%E8%BF%98%E5%8F%AF%E4%BB%A5%E5%AF%B9%E7%94%A8%E6%88%B7%E7%9A%84%E8%BE%93%E5%85%A5%E8%BF%9B%E8%A1%8C%E5%88%86%E6%9E%90%E6%A3%80%E6%9F%A5%E5%B9%B6%E4%BD%9C%E7%9B%B8%E5%BA%94%E7%9A%84%E5%A4%84%E7%90%86%EF%BC%9B %E6%98%BE%E7%A4%BA%E7%94%B1%E6%9C%8D%E5%8A%A1%E5%99%A8%E7%AB%AF%E9%AB%98%E5%B1%82%E4%BC%A0%E6%9D%A5%E7%9A%84%E8%BF%90%E8%A1%8C%E7%BB%93%E6%9E%9C%E3%80%82 %E5%AE%A2%E6%88%B7%E5%B1%82%E9%80%9A%E5%B8%B8%E6%98%AF%E7%94%B1%E5%AE%A2%E6%88%B7%E8%BF%9B%E7%A8%8B%E7%BB%84%E6%88%90%EF%BC%8C%E8%BF%99%E4%BA%9B%E8%BF%9B%E7%A8%8B%E7%94%B1%E6%B5%8F%E8%A7%88%E5%99%A8%E5%8A%A8%E6%80%81%E5%9C%B0%E5%88%9B%E5%BB%BA%E5%92%8C%E6%92%A4%E9%94%80%E3%80%82 %E4%B8%9A%E5%8A%A1%E9%80%BB%E8%BE%91%E5%B1%82 %E8%BF%99%E6%98%AF%E6%95%B4%E4%B8%AA%E7%B3%BB%E7%BB%9F%E6%9C%80%E5%85%B3%E9%94%AE%E7%9A%84%E9%83%A8%E5%88%86%E3%80%82%E4%B8%9A%E5%8A%A1%E9%80%BB%E8%BE%91%E5%B1%82%E5%9C%A8%E9%80%9A%E5%B8%B8%E6%83%85%E5%86%B5%E4%B8%8B%E4%BC%9A%E5%88%86%E4%B8%BA%E4%B8%A4%E5%B1%82%EF%BC%8C%E5%85%B6%E9%AB%98%E5%B1%82%E6%98%AF%E8%AF%B7%E6%B1%82%E6%8E%A5%E6%94%B6%E5%B1%82%EF%BC%88%E4%B8%80%E8%88%AC%E7%A7%B0%E4%B9%8B%E4%B8%BAWeb%E5%B1%82%EF%BC%89%EF%BC%8C%E7%94%A8%E4%BA%8E%E6%8E%A5%E6%94%B6%E4%BB%8E%E6%B5%8F%E8%A7%88%E5%99%A8%E4%BC%A0%E6%9D%A5%E7%9A%84%E8%AF%B7%E6%B1%82%E5%B9%B6%E5%B0%86%E8%AF%B7%E6%B1%82%E4%BA%A4%E7%BB%99%E5%BA%95%E5%B1%82%E8%BF%9B%E8%A1%8C%E5%A4%84%E7%90%86%EF%BC%8C%E5%90%8C%E6%97%B6%E5%B0%86%E8%AF%B7%E6%B1%82%E5%A4%84%E7%90%86%E7%BB%93%E6%9E%9C%E5%8F%91%E9%80%81%E7%BB%99%E6%B5%8F%E8%A7%88%E5%99%A8%E3%80%82%E8%BF%99%E4%BA%9B%E8%BF%87%E7%A8%8B%E4%B8%BB%E8%A6%81%E7%94%B1JSP%E9%A1%B5%E9%9D%A2%E3%80%81%E5%9F%BA%E4%BA%8EWeb%E7%9A%84Applets%E4%BB%A5%E5%8F%8A%E6%98%BE%E7%A4%BA HTML%E9%A1%B5%E9%9D%A2%E7%9A%84Servlets%E7%BB%84%E6%88%90%E3%80%82%E5%BA%95%E5%B1%82%E6%98%AF%E8%AF%B7%E6%B1%82%E5%A4%84%E7%90%86%E5%B1%82%EF%BC%88%E4%B8%80%E8%88%AC%E7%A7%B0%E4%B9%8B%E4%B8%BAEJB%E5%B1%82%EF%BC%89%EF%BC%8C%E5%8C%85%E6%8B%AC%E7%9B%91%E5%90%AC%E8%BF%9B%E7%A8%8B%E3%80%81%E5%A4%84%E7%90%86%E8%BF%9B%E7%A8%8B%E5%92%8C%E6%95%B0%E6%8D%AE%E5%BA%93%E6%93%8D%E4%BD%9C%E8%BF%9B%E7%A8%8B%EF%BC%8C%E8%B4%9F%E8%B4%A3%E5%A4%84%E7%90%86%E8%AF%B7%E6%B1%82%E6%8E%A5%E6%94%B6%E5%B1%82%E4%BC%A0%E6%9D%A5%E7%9A%84%E5%AE%A2%E6%88%B7%E8%AF%B7%E6%B1%82%E5%B9%B6%E5%AF%B9%E5%AE%83%E8%BF%9B%E8%A1%8C%E5%A4%84%E7%90%86%EF%BC%8C%E5%90%8C%E6%97%B6%E5%B0%86%E8%AF%B7%E6%B1%82%E7%BB%93%E6%9E%9C%E4%BC%A0%E9%80%92%E7%BB%99%E8%AF%B7%E6%B1%82%E6%8E%A5%E6%94%B6%E5%B1%82%EF%BC%8C%E5%A6%82%E6%9E%9C%E9%9C%80%E8%A6%81%E7%9A%84%E8%AF%9D%E8%BF%98%E9%9C%80%E8%A6%81%E5%B0%86%E5%A4%84%E7%90%86%E7%BB%93%E6%9E%9C%E4%BA%A4%E7%BB%99%E6%95%B0%E6%8D%AE%E5%B1%82%E8%BF%9B%E8%A1%8C%E5%AD%98%E5%82%A8%E3%80%82 %E6%95%B0%E6%8D%AE%E5%B1%82 %E4%B8%BB%E8%A6%81%E6%98%AF%E4%B8%BA%E4%B8%9A%E5%8A%A1%E9%80%BB%E8%BE%91%E5%B1%82%E6%8F%90%E4%BE%9B%E6%95%B0%E6%8D%AE%E6%9C%8D%E5%8A%A1%EF%BC%8C%E5%A6%82%E5%AD%98%E5%82%A8%E4%B8%9A%E5%8A%A1%E9%80%BB%E8%BE%91%E5%B1%82%E5%A4%84%E7%90%86%E7%BB%93%E6%9E%9C%E3%80%81%E8%BF%94%E5%9B%9E%E4%B8%9A%E5%8A%A1%E9%80%BB%E8%BE%91%E5%B1%82%E6%A3%80%E7%B4%A2%E7%9A%84%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%9C%EF%BC%8C%E5%90%8C%E6%97%B6%E4%B9%9F%E6%98%AF%E4%B8%BA%E4%BA%86%E5%AE%9E%E7%8E%B0%E5%B1%8F%E8%94%BD%E6%95%B0%E6%8D%AE%E6%BA%90%E7%9A%84%E5%8F%98%E5%8C%96%EF%BC%8C%E4%BB%8E%E8%80%8C%E5%AE%9E%E7%8E%B0%E5%BD%93%E6%95%B0%E6%8D%AE%E5%BA%93%E5%8F%91%E7%94%9F%E5%8F%98%E5%8C%96%E6%97%B6%E6%88%91%E4%BB%AC%E5%8F%AA%E9%9C%80%E4%BF%AE%E6%94%B9%E8%BF%9E%E6%8E%A5%E6%95%B0%E6%8D%AE%E6%BA%90%E7%9A%84%E8%AF%AD%E5%8F%A5%E5%B0%B1%E5%8F%AF%E4%BB%A5%E3%80%82 EJB%E7%BB%84%E4%BB%B6%E7%9A%84%E5%88%86%E7%B1%BB %E9%80%9A%E5%B8%B8%E6%83%85%E5%86%B5%E4%B8%8B%EF%BC%8C%E6%9C%8D%E5%8A%A1%E7%AB%AF%E7%9A%84EJB%E7%BB%84%E4%BB%B6%E6%9C%89%E4%B8%A4%E7%A7%8D%E5%9F%BA%E6%9C%AC%E7%B1%BB%E5%9E%8B%EF%BC%9AEntity Bean%EF%BC%88%E5%AE%9E%E4%BD%93Bean%EF%BC%89%E5%92%8CSession Bean%EF%BC%88%E4%BC%9A%E8%AF%9DBean%EF%BC%89%E3%80%82