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写给JSP初级程序员的书

　　 下面这个例子寻找表单所发送的所有变量名字，并把它们放入表格中，没有值或者有多个值的变量都突出显示。 <br>
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　　 首先，程序通过HttpServletRequest的getParameterNames方法得到所有的变量名字，getParameterNames返回的是一个Enumeration。接下来，程序用循环遍历这个Enumeration，通过hasMoreElements确定何时结束循环，利用nextElement得到Enumeration中的各个项。由于nextElement返回的是一个Object，程序把它转换成字符串后再用这个字符串来调用getParameterValues。 <br>
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　　 getParameterValues返回一个字符串数组，如果这个数组只有一个元素且等于空字符串，说明这个表单变量没有值，Servlet以斜体形式输出“No Value”；如果数组元素个数大于1，说明这个表单变量有多个值，Servlet以HTML列表形式输出这些值；其他情况下Servlet直接把变量值放入表格。 <br>
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　　 ShowParameters.java <br>
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　　 注意，ShowParameters.java用到了前面介绍过的ServletUtilities.java。 <br>
package hall;<br>
<br>
import java.io.*;<br>
import javax.servlet.*;<br>
import javax.servlet.http.*;<br>
import java.util.*;<br>
<br>
public class ShowParameters extends HttpServlet {<br>
&nbsp;&nbsp;public void doGet(HttpServletRequest request,<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;HttpServletResponse response)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;throws ServletException, IOException {<br>
&nbsp;&nbsp;&nbsp;&nbsp;response.setContentType(&quot;text/html&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;PrintWriter out = response.getWriter();<br>
&nbsp;&nbsp;&nbsp;&nbsp;String title = &quot;读取所有请求参数&quot;;<br>
&nbsp;&nbsp;&nbsp;&nbsp;out.println(ServletUtilities.headWithTitle(title) +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;＜BODY BGCOLOR=＼&quot;#FDF5E6＼&quot;＞＼n&quot; +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;＜H1 ALIGN=CENTER＞&quot; + title + &quot;＜/H1＞＼n&quot; +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;＜TABLE BORDER=1 ALIGN=CENTER＞＼n&quot; +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;＜TR BGCOLOR=＼&quot;#FFAD00＼&quot;＞＼n&quot; +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;＜TH＞参数名字＜TH＞参数值&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;Enumeration paramNames = request.getParameterNames();<br>
&nbsp;&nbsp;&nbsp;&nbsp;while(paramNames.hasMoreElements()) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String paramName = (String)paramNames.nextElement();<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜TR＞＜TD＞&quot; + paramName + &quot;＼n＜TD＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String[] paramValues = request.getParameterValues(paramName);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (paramValues.length == 1) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String paramValue = paramValues[0];<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (paramValue.length() == 0)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.print(&quot;＜I＞No Value＜/I＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.print(paramValue);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} else {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜UL＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for(int i=0; i＜paramValues.length; i++) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜LI＞&quot; + paramValues[i]);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜/UL＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜/TABLE＞＼n＜/BODY＞＜/HTML＞&quot;);<br>
&nbsp;&nbsp;}<br>
<br>
&nbsp;&nbsp;public void doPost(HttpServletRequest request,<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;HttpServletResponse response)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;throws ServletException, IOException {<br>
&nbsp;&nbsp;&nbsp;&nbsp;doGet(request, response);<br>
&nbsp;&nbsp;}<br>
}<br>
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　　 测试表单 <br>
<br>
　　 下面是向上述Servlet发送数据的表单PostForm.html。就像所有包含密码输入域的表单一样，该表单用POST方法发送数据。我们可以看到，在Servlet中同时实现doGet和doPost这两种方法为表单制作带来了方便。 <br>
＜!DOCTYPE HTML PUBLIC &quot;-//W3C//DTD HTML 4.0 Transitional//EN&quot;＞<br>
＜HTML＞<br>
＜HEAD＞<br>
&nbsp;&nbsp;＜TITLE＞示例表单＜/TITLE＞<br>
＜/HEAD＞<br>
<br>
＜BODY BGCOLOR=&quot;#FDF5E6&quot;＞<br>
＜H1 ALIGN=&quot;CENTER&quot;＞用POST方法发送数据的表单＜/H1＞<br>
<br>
＜FORM ACTION=&quot;/servlet/hall.ShowParameters&quot;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;METHOD=&quot;POST&quot;＞<br>
&nbsp;&nbsp;Item Number:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;itemNum&quot;＞＜BR＞<br>
&nbsp;&nbsp;Quantity:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;quantity&quot;＞＜BR＞<br>
&nbsp;&nbsp;Price Each:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;price&quot; VALUE=&quot;$&quot;＞＜BR＞<br>
&nbsp;&nbsp;＜HR＞<br>
&nbsp;&nbsp;First Name:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;firstName&quot;＞＜BR＞<br>
&nbsp;&nbsp;Last Name:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;lastName&quot;＞＜BR＞<br>
&nbsp;&nbsp;Middle Initial:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;initial&quot;＞＜BR＞<br>
&nbsp;&nbsp;Shipping Address:<br>
&nbsp;&nbsp;＜TEXTAREA NAME=&quot;address&quot; ROWS=3 COLS=40＞＜/TEXTAREA＞＜BR＞<br>
&nbsp;&nbsp;Credit Card:＜BR＞<br>
&nbsp;&nbsp;&nbsp;&nbsp;＜INPUT TYPE=&quot;RADIO&quot; NAME=&quot;cardType&quot;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;VALUE=&quot;Visa&quot;＞Visa＜BR＞<br>
&nbsp;&nbsp;&nbsp;&nbsp;＜INPUT TYPE=&quot;RADIO&quot; NAME=&quot;cardType&quot;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;VALUE=&quot;Master Card&quot;＞Master Card＜BR＞<br>
&nbsp;&nbsp;&nbsp;&nbsp;＜INPUT TYPE=&quot;RADIO&quot; NAME=&quot;cardType&quot;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;VALUE=&quot;Amex&quot;＞American Express＜BR＞<br>
&nbsp;&nbsp;&nbsp;&nbsp;＜INPUT TYPE=&quot;RADIO&quot; NAME=&quot;cardType&quot;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;VALUE=&quot;Discover&quot;＞Discover＜BR＞<br>
&nbsp;&nbsp;&nbsp;&nbsp;＜INPUT TYPE=&quot;RADIO&quot; NAME=&quot;cardType&quot;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;VALUE=&quot;Java SmartCard&quot;＞Java SmartCard＜BR＞<br>
&nbsp;&nbsp;Credit Card Number:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;PASSWORD&quot; NAME=&quot;cardNum&quot;＞＜BR＞<br>
&nbsp;&nbsp;Repeat Credit Card Number:<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;PASSWORD&quot; NAME=&quot;cardNum&quot;＞＜BR＞＜BR＞<br>
&nbsp;&nbsp;＜CENTER＞<br>
&nbsp;&nbsp;&nbsp;&nbsp;＜INPUT TYPE=&quot;SUBMIT&quot; VALUE=&quot;Submit Order&quot;＞<br>
&nbsp;&nbsp;＜/CENTER＞<br>
＜/FORM＞<br>
<br>
＜/BODY＞<br>
＜/HTML＞      <br>   
      <br>   
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