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写给JSP初级程序员的书

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　　 注意，该Servlet要用到前面给出的ServletUtilities.java。另外还要用到：PrimeList.java，用于在后台线程中创建一个素数的Vector；Primes.java，用于随机生成BigInteger类型的大数字，检查它们是否是素数。（此处略去PrimeList.java和Primes.java的代码。） <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 PrimeNumbers extends HttpServlet {<br>
&nbsp;&nbsp;private static Vector primeListVector = new Vector();<br>
&nbsp;&nbsp;private static int maxPrimeLists = 30;<br>
&nbsp;&nbsp;<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;int numPrimes = ServletUtilities.getIntParameter(request, &quot;numPrimes&quot;, 50);<br>
&nbsp;&nbsp;&nbsp;&nbsp;int numDigits = ServletUtilities.getIntParameter(request, &quot;numDigits&quot;, 120);<br>
&nbsp;&nbsp;&nbsp;&nbsp;PrimeList primeList = findPrimeList(primeListVector, numPrimes, numDigits);<br>
&nbsp;&nbsp;&nbsp;&nbsp;if (primeList == null) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;primeList = new PrimeList(numPrimes, numDigits, true);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;synchronized(primeListVector) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (primeListVector.size() ＞= maxPrimeLists)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;primeListVector.removeElementAt(0);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;primeListVector.addElement(primeList);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;&nbsp;Vector currentPrimes = primeList.getPrimes();<br>
&nbsp;&nbsp;&nbsp;&nbsp;int numCurrentPrimes = currentPrimes.size();<br>
&nbsp;&nbsp;&nbsp;&nbsp;int numPrimesRemaining = (numPrimes - numCurrentPrimes);<br>
&nbsp;&nbsp;&nbsp;&nbsp;boolean isLastResult = (numPrimesRemaining == 0);<br>
&nbsp;&nbsp;&nbsp;&nbsp;if (!isLastResult) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;response.setHeader(&quot;Refresh&quot;, &quot;5&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;}<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;Some &quot; + numDigits + &quot;-Digit Prime Numbers&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;＜H2 ALIGN=CENTER＞&quot; + title + &quot;＜/H2＞＼n&quot; +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;＜H3＞Primes found with &quot; + numDigits +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot; or more digits: &quot; + numCurrentPrimes + &quot;.＜/H3＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;if (isLastResult)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜B＞Done searching.＜/B＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;else<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜B＞Still looking for &quot; + numPrimesRemaining +<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot; more＜BLINK＞...＜/BLINK＞＜/B＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜OL＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;for(int i=0; i＜numCurrentPrimes; i++) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;&nbsp;&nbsp;＜LI＞&quot; + currentPrimes.elementAt(i));<br>
&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜/OL＞&quot;);<br>
&nbsp;&nbsp;&nbsp;&nbsp;out.println(&quot;＜/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>
&nbsp;&nbsp;// 检查是否存在同类型请求（已经完成，或者正在计算）。<br>
&nbsp;&nbsp;// 如存在，则返回现有结果而不是启动新的后台线程。<br>
&nbsp;&nbsp;private PrimeList findPrimeList(Vector primeListVector,<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int numPrimes,<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int numDigits) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;synchronized(primeListVector) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for(int i=0; i＜primeListVector.size(); i++) {<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;PrimeList primes = (PrimeList)primeListVector.elementAt(i);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if ((numPrimes == primes.numPrimes()) &amp;&amp;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(numDigits == primes.numDigits()))<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return(primes);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return(null);<br>
&nbsp;&nbsp;&nbsp;&nbsp;}<br>
&nbsp;&nbsp;}<br>
}<br>
<br>
<br>
<br>
<br>
　　 PrimeNumbers.html <br>
＜!DOCTYPE HTML PUBLIC &quot;-//W3C//DTD HTML 4.0 Transitional//EN&quot;＞<br>
＜HTML＞<br>
＜HEAD＞<br>
&nbsp;&nbsp;＜TITLE＞大素数计算＜/TITLE＞<br>
＜/HEAD＞<br>
＜CENTER＞<br>
＜BODY BGCOLOR=&quot;#FDF5E6&quot;＞<br>
＜FORM ACTION=&quot;/servlet/hall.PrimeNumbers&quot;＞<br>
&nbsp;&nbsp;＜B＞要计算几个素数:＜/B＞<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;numPrimes&quot; VALUE=25 SIZE=4＞＜BR＞<br>
&nbsp;&nbsp;＜B＞每个素数的位数:＜/B＞<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;TEXT&quot; NAME=&quot;numDigits&quot; VALUE=150 SIZE=3＞＜BR＞<br>
&nbsp;&nbsp;＜INPUT TYPE=&quot;SUBMIT&quot; VALUE=&quot;开始计算&quot;＞<br>
＜/FORM＞<br>
＜/CENTER＞<br>
＜/BODY＞<br>
＜/HTML＞      <br>   
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