📄 jb7-1-1.htm
字号:
<HTML>
<HEAD>
<META NAME="GENERATOR" Content="Microsoft FrontPage 4.0">
<TITLE></TITLE>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
</HEAD>
<body bgcolor="#fefef2" style="FONT-SIZE: 9pt">
<P><STRONG><FONT
color=#0080FF size=3 >EJB开发介绍
</FONT>
</STRONG>
<hr>
译者名字: genode(JD015)<br>
邮件地址:<a href="mailto:genode@sina.com">genode@sina.com</a>
<p class="MsoNormal" style="margin-left:.85gd;text-indent:27.1pt;mso-char-indent-count:
2.58;mso-char-indent-size:10.5pt"><span lang="EN-US">Enterprise JavaBeans(EJB)</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">规范正式地定义了针对应用服务器的</span><span lang="EN-US">Java</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">服务器端组件和编程接口。开发人员构建称为</span><span lang="EN-US">enterprise
beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">的组件来封装企业的商业逻辑。</span><span lang="EN-US">Enterprise
beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">运行于一个</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">服务器上，由后者为其提供事务管理和安全保证。开发人员无须对这些底层的复杂的服务编程，而可以将精力集中于将组织或系统的商业规则封装入</span><span lang="EN-US">beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">，只需知道在需要的时候</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">服务器会提供相应服务的。</span></p>
<p class="MsoNormal" style="margin-left:.85gd;text-indent:27.1pt;mso-char-indent-count:
2.58;mso-char-indent-size:10.5pt"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">虽然</span><span lang="EN-US">Enterprise
JavaBeans</span><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">规范对于</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">框架的说明是最为权威的，但它主要对开发商</span><span lang="EN-US">,
</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">列如构建</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">服务器和</span><span lang="EN-US">beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">容器的</span><span lang="EN-US">Borland</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">公司有用。本书将帮助</span><span lang="EN-US">JBuilder</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">开发人员学习开发</span><span lang="EN-US">enterprise
beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">的必备知识，并创建应用程序来使用它们。</span></p>
<p class="MsoNormal" style="margin-left:.85gd;text-indent:27.1pt;mso-char-indent-count:
2.58;mso-char-indent-size:10.5pt"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">如果你已经熟悉了</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">的开发，想要开始用</span><span lang="EN-US">JBuilder</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">创建</span><span lang="EN-US">enterprise beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">，进入“用</span><span lang="EN-US">Jbuilder</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">开发</span><span lang="EN-US">enterprise beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">”。</span></p>
<hr>
<p><b><font size="3"><font color="#000080">为什么我们需要Enterprise
JavaBeans</font><o:p>
</font>
</o:p>
</b></p>
<p class="MsoNormal" style="margin-left:.85gd;text-indent:27.1pt;mso-char-indent-count:
2.58;mso-char-indent-size:10.5pt"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">在应用程序开发中，客户端</span><span lang="EN-US">—</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">服务器端模型相当流行。客户端应用程序驻留于本地机器访问数据存储库比如关系数据管理系统（</span><span lang="EN-US">RDMS</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">）中的数据。这一模型在仅有少量用户的系统中工作良好。但当越来越多的用户需要访问数据时，这些应用程序并不能很好的满足要求。因为客户端包含商业逻辑，它必须安装在每台客户机上。这样使管理上越来越困难。</span></p>
<p class="MsoNormal" style="margin-left:.85gd;text-indent:27.1pt;mso-char-indent-count:
2.58;mso-char-indent-size:10.5pt"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">逐渐的，将应用程序的客户端</span><span lang="EN-US">—</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">服务器端模型分割为多于两层的优势变得明显了。在一个多层应用程序中，只将用户接口驻留在客户机上，而应用程序的逻辑运行于服务器上的中间层上。最终的一层仍然存储着数据。当一个应用程序的逻辑需要更新时，只需修改服务器上的中间层的软件，这使得更新管理变得相当简单。</span></p>
<p class="MsoNormal" style="margin-left:.85gd;text-indent:27.1pt;mso-char-indent-count:
2.58;mso-char-indent-size:10.5pt"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">但是创建可靠、安全、易于管理的分布式应用程序的难度是众人皆知的。比如对分布式系统的事务处理是一项主要任务。幸运的是，按照如下的</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">规范运用组件来构建分布式系统能减轻许多负担：</span></p>
<p class="MsoNormal" style="margin-left:57.0pt;text-indent:-21.0pt;mso-list:l0 level1 lfo1;
tab-stops:list 57.0pt"><span lang="EN-US" style="font-family:
Wingdings">l<span style="font:7.0pt "Times New Roman""> </span></span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">将分布式系统的开发分割为明确的任务分配给专家们。</span></p>
<p class="MsoNormal" style="margin-left:5.14gd"><span style="font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">例如，这个应用程序是会计系统，则</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">组件开发者</span><span lang="EN-US">(Enterprise
Bean Developer) </span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">需要理解会计业务。系统管理员（</span><span lang="EN-US">system<span style="mso-spacerun: yes">
</span>administrator</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">）必须负责应用程序的监测部署和运行情况。每一个专家都假设为一个特定角色。</span></p>
<p class="MsoNormal" style="margin-left:57.0pt;text-indent:-21.0pt;mso-list:l0 level1 lfo1;
tab-stops:list 57.0pt"><span lang="EN-US" style="font-family:
Wingdings">l<span style="font:7.0pt "Times New Roman""> </span></span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">使得</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">服务器和容器能为</span><span lang="EN-US">enterprise
beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">和应用程序开发人员提供服务。</span></p>
<p class="MsoNormal" style="margin-left:57.0pt"><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">服务器提供者</span><span lang="EN-US">(EJB
Server Provider)</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">和</span><span lang="EN-US">EJB </span><span style="font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">容器提供者</span><span lang="EN-US">(EJB
Container Provider)</span><span style="font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">（他们通常是同一个开发商）处理许多更难的任务，使得开发人员不必关心这些细节。比如，运行</span><span lang="EN-US">enterprise
beans</span><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">的容器，自动为</span><span lang="EN-US">beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">提供了事务和安全服务。</span></p>
<p class="MsoNormal" style="margin-left:57.0pt;text-indent:-21.0pt;mso-list:l0 level1 lfo1;
tab-stops:list 57.0pt"><span lang="EN-US" style="font-family:
Wingdings">l<span style="font:7.0pt "Times New Roman""> </span></span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">使得</span><span lang="EN-US">enterprise
beans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">具有可移植性。</span></p>
<p class="MsoNormal" style="margin-left:54.0pt"><span style="font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">一旦一个</span><span lang="EN-US">bean</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">编写完成，它可以被部署在符合</span><span lang="EN-US">Enterprise
JavaBeans</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">标准的任何</span><span lang="EN-US">EJB</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">服务器上。但是每一个</span><span lang="EN-US">bean</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">可能包括开发商的特殊元件。</span></p>
<hr>
<p><b><span lang="EN-US"><font color="#000080" size="3">EJB</font></span><font color="#000080" size="3"><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">应用程序开发中的角色</span></font><span lang="EN-US"><o:p>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -