JSP中设置HTTP应答头

primenumbers.java

　　 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。）
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);
}

// 检查是否存在同类型请求（已经完成，或者正在计算）。
// 如存在，则返回现有结果而不是启动新的后台线程。
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＞大素数计算＜/title＞
＜/head＞
＜center＞
＜body bgcolor="#fdf5e6"＞
＜form action="/servlet/hall.primenumbers"＞
＜b＞要计算几个素数:＜/b＞
＜input type="text" name="numprimes" value=25 size=4＞＜br＞
＜b＞每个素数的位数:＜/b＞
＜input type="text" name="numdigits" value=150 size=3＞＜br＞
＜input type="submit" value="开始计算"＞
＜/form＞
＜/center＞
＜/body＞
＜/html＞