15.html

写给JSP初级程序员的书

      <P class=MsoNormal><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">然而基于</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">平台的应用程序可被部署到各种操作系统上。例如可被部署到高端</SPAN><SPAN 
      lang=EN-US>UNIX</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">与大型机系统，这种系统单机可支持</SPAN><SPAN 
      lang=EN-US>64</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">至</SPAN><SPAN 
      lang=EN-US>256</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">个处理器。</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">领域的供应商提供了更为广泛的负载平衡策略。能消除系统中的瓶颈，允许多台服务器集成部署。这种部署可达数千个处理器，实现可高度伸缩的系统，满足未来商业应用的需要。</SPAN></P>
      <P class=MsoNormal><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
      <P class=MsoNormal><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">通过伸缩性的例子，我们也可看出选择专有技术如</SPAN><SPAN 
      lang=EN-US>WINDOWS DNA</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的危险性。客户没有选择余地，只能等待供应商完成指定的特性。然而选择</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">这种开放结构，客户可以选择产品，还能保留在现有应用开发方面的投资。如果基于</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">平台的应用程序设计正确，客户可以变更产品供应商，以最小的移植代价来满足一定的伸缩性或功能需要。</SPAN></P>
      <P class=MsoNormal><B style="mso-bidi-font-weight: normal"><SPAN 
      lang=EN-US style="FONT-SIZE: 16pt; mso-bidi-font-size: 10.0pt"><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></B></P>
      <P class=MsoNormal><B style="mso-bidi-font-weight: normal"><SPAN 
      lang=EN-US 
      style="FONT-SIZE: 16pt; mso-bidi-font-size: 10.0pt">7</SPAN></B><B 
      style="mso-bidi-font-weight: normal"><SPAN 
      style="FONT-FAMILY: 宋体; FONT-SIZE: 16pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-bidi-font-size: 10.0pt">长期的可用性</SPAN></B><B 
      style="mso-bidi-font-weight: normal"><SPAN lang=EN-US 
      style="FONT-SIZE: 16pt; mso-bidi-font-size: 10.0pt"><o:p></o:p></SPAN></B></P>
      <P class=MsoNormal><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">一个服务器端平台必须能全天候运转以满足公司客户、合作伙伴的需要。因为</SPAN><SPAN 
      lang=EN-US>INTERNET</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是全球化的、无处不在的，即使在夜间按计划停机也可能造成严重损失。若是意外停机，那会有灾难性后果。随着</SPAN><SPAN 
      lang=EN-US>INTERNET</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">越来越成为主要的交易平台，这种事态现着愈发严重了。</SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">部署到可靠的操作环境中，他们支持长期的可用性。一些</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">部署在</SPAN><SPAN 
      lang=EN-US>WINDOWS</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">环境中，客户也可选择健壮性能更好的操作系统如</SPAN><SPAN 
      lang=EN-US>Sun'sSolaris</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</SPAN><SPAN 
      lang=EN-US>IBM OS/390</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。最健壮的操作系统可达到</SPAN><SPAN 
      lang=EN-US>99.999%</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的可用性或每年只需</SPAN><SPAN 
      lang=EN-US>5</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">分钟停机时间。这是实时性很强商业系统理想的选择。</SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">基于微软技术的部署过去还不能达到这样高水平的可用性。</SPAN><SPAN 
      lang=EN-US>WINDOWS DNA</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">绑在</SPAN><SPAN 
      lang=EN-US>WINDOWS </SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">操作系统上，而这种操作系统过去一直由于可靠性不高受到批评。微软自己高度赞扬他的</SPAN><SPAN 
      lang=EN-US>WIN 2000</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">具有高度的可用性。但是否能达到以上这些操作系统的水平仍待观察。尽管微软的一些老客户要选择</SPAN><SPAN 
      lang=EN-US>WINDOWS 2000,</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">任务时实性很强主流商务站点会采取保守姿态。</SPAN></P>
      <P class=MsoNormal><B style="mso-bidi-font-weight: normal"><SPAN 
      lang=EN-US style="FONT-SIZE: 16pt; mso-bidi-font-size: 10.0pt"><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></B></P>
      <P class=MsoNormal><B style="mso-bidi-font-weight: normal"><SPAN 
      lang=EN-US 
      style="FONT-SIZE: 16pt; mso-bidi-font-size: 10.0pt">8</SPAN></B><B 
      style="mso-bidi-font-weight: normal"><SPAN 
      style="FONT-FAMILY: 宋体; FONT-SIZE: 16pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-bidi-font-size: 10.0pt">产品的总体成本</SPAN></B></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">购买服务器端平台，我们必须考虑拥有这个产品的总体成本。它包括：服务器平台的价格、在这个平台上开发和改进方案的成本、维护费用、由于伸缩性、不稳定性问题所消耗的部署时间、由于平台的缺陷所损失的客户。较低的总体成本是拥有大宗业务、要求时实性强的商业站点所必需的。</SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">基于</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">平台的产品价位范围很广，各种类型的公司都可以找到满足他们预算水平，所需求服务的产品。产品有完全免费（如代码公开的</SPAN><SPAN 
      lang=EN-US>Bullsoft's JOnAS</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）、每机</SPAN><SPAN 
      lang=EN-US>2500</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">美元</SPAN><SPAN 
      lang=EN-US>(Valto's Ejipt)</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、每</SPAN><SPAN 
      lang=EN-US>CPU35000</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">美元</SPAN><SPAN 
      lang=EN-US>(IBM's WebSphere Enterprise Edition)</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。而微软指定的最初价位是：</SPAN><SPAN 
      lang=EN-US>Windows 2000 Advanced Server</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">每机</SPAN><SPAN 
      lang=EN-US>3999</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">美元外加</SPAN><SPAN 
      lang=EN-US>1999</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">美元（由于</SPAN><SPAN 
      lang=EN-US>INTERNET</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">连接造成无限授权的</SPAN><SPAN 
      lang=EN-US>INTERNET</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">用户）。</SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">微软的价位是处在基于</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">产品价位的中低档。微软还没有宣布</SPAN><SPAN 
      lang=EN-US>Windows 2000 Datacenter Server, Windows 2000 AppCenter 
      Server</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">价格，因此现在我们还无法把微软的高端平台与大部分</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">平台相比。以后会因为竞争的存在，各中间件供应商包括微软会按照所提供的服务水平而达成相近的价位。</SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN lang=EN-US><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></SPAN></P>
      <P align=left class=MsoNormal 
      style="TEXT-ALIGN: left; mso-layout-grid-align: none"><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">无论价格战的结果如何，</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">架构都会比</SPAN><SPAN 
      lang=EN-US>Windows DNA</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">节省更多的整体成本。这是因为采用</SPAN><SPAN 
      lang=EN-US>J2EE</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">架构，</SPAN><SPAN 
      lang=EN-US>IT</SPAN><SPAN 
      style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">部门可更充分利用在应用程序、中间件技术、操作系统方面已有的投资。基于</SPAN><SPAN 
      lang=EN-US>J2EE