下载功能时报错 ERROR [Engine] StandardWrapperValve[jsp]: Servlet.service() for servlet jsp threw exception

代码如下:
//DownLoda.java
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.net.*;
import Com.Fh.Xtpt.Servers.PubServers;

/**
* 实现下载功能
*/
public class DownLoad {

public void downLoad(HttpServletResponse response, String headName,
String fileUrl) throws Exception {

if (headName.endsWith(".txt")) {
response.setContentType("text;charset=GB2312");
response.setHeader("Content-disposition",
"attachment; filename=" + headName);
}
else {
response.setContentType("application/doc;charset=GB2312");
response.setHeader("Content-disposition",
"attachment; filename=" + headName);
}

String fileURL = fileUrl;
if (fileURL == null) {
return;
}

try {
File file = new File(fileUrl);
FileInputStream bis = new FileInputStream(file);
OutputStream bos = response.getOutputStream();

byte[] buff = new byte[1024];
int readCount = 0;
int i = 0;
readCount = bis.read(buff);
while (readCount != -1) {
bos.write(buff, 0, readCount);
readCount = bis.read(buff);
}

if (bis != null) {
System.out.println("****** good1 ******");
bis.close();
System.out.println("****** good2 ******");
}
if (bos != null) {
System.out.println("****** good3 ******");
bos.close();