在JSP中設置HTTP應答頭

本文介紹在JSP中設置HTTP應答頭的文章專題。

PrimeNumbers.java

　　 注意，該Servlet要用到前面給出的ServletUtilities.java。另外還要用到：PrimeList.java，用於在後臺線程中創建一個素數的Vector；Primes.java，用於隨機生成BigInteger類型的大數字，檢查它們是否是素數。（此處略去 PrimeList.java和Primes.java的代碼。）
package hall;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;

public class PrimeNumbers extends HttpServlet {
private static Vector primeListVector = new Vector();
private static int maxPrimeLists = 30;

public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
int numPrimes = ServletUtilities.getIntParameter(request, "numPrimes", 50);
int numDigits = ServletUtilities.getIntParameter(request, "numDigits", 120);
PrimeList primeList = findPrimeList(primeListVector, numPrimes, numDigits);
if (primeList == null) {
primeList = new PrimeList(numPrimes, numDigits, true);
synchronized(primeListVector) {
if (primeListVector.size() ＞= maxPrimeLists)
primeListVector.removeElementAt(0);
primeListVector.addElement(primeList);
}
}
Vector currentPrimes = primeList.getPrimes();
int numCurrentPrimes = currentPrimes.size();
int numPrimesRemaining = (numPrimes - numCurrentPrimes);
boolean isLastResult = (numPrimesRemaining == 0);
if (!isLastResult) {
response.setHeader("Refresh", "5");
}
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "Some " + numDigits + "-Digit Prime Numbers";
out.println(ServletUtilities.headWithTitle(title) +
"＜BODY BGCOLOR=＼"#FDF5E6＼"＞＼n" +
"＜H2 ALIGN=CENTER＞" + title + "＜/H2＞＼n" +
"＜H3＞Primes found with " + numDigits +
" or more digits: " + numCurrentPrimes + ".＜/H3＞");
if (isLastResult)
out.println("＜B＞Done searching.＜/B＞");
else
out.println("＜B＞Still looking for " + numPrimesRemaining +
" more＜BLINK＞...＜/BLINK＞＜/B＞");
out.println("＜OL＞");
for(int i=0; i＜numCurrentPrimes; i++) {
out.println(" ＜LI＞" + currentPrimes.elementAt(i));
}
out.println("＜/OL＞");
out.println("＜/BODY＞＜/HTML＞");
}

public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}

// 檢查是否存在同類型請求（已經完成，或者正在計算）。
// 如存在，則返回現有結果而不是啓動新的後臺線程。
private PrimeList findPrimeList(Vector primeListVector,
int numPrimes,
int numDigits) {
synchronized(primeListVector) {
for(int i=0; i＜primeListVector.size(); i++) {
PrimeList primes = (PrimeList)primeListVector.elementAt(i);
if ((numPrimes == primes.numPrimes()) &&
(numDigits == primes.numDigits()))
return(primes);
}
return(null);
}
}
}

　　 PrimeNumbers.html

＜!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"＞
＜HTML＞
＜HEAD＞
＜TITLE＞大素數計算＜/TITLE＞
＜/HEAD＞
＜CENTER＞
＜BODY BGCOLOR="#FDF5E6"＞
＜FORM ACTION="/servlet/hall.PrimeNumbers"＞
＜B＞要計算幾個素數:＜/B＞
＜INPUT TYPE="TEXT" NAME="numPrimes" VALUE=25 SIZE=4＞＜BR＞
＜B＞每個素數的位數:＜/B＞
＜INPUT TYPE="TEXT" NAME="numDigits" VALUE=150 SIZE=3＞＜BR＞
＜INPUT TYPE="SUBMIT" VALUE="開始計算"＞
＜/FORM＞
＜/CENTER＞
＜/BODY＞
＜/HTML＞