用Jsp来实现文件下载功能的几种方式介绍

public void service(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType(" text/plain ");
OutputStream outputStream = null;
try {
outputStream = res.getOutputStream();
//把文件路径为srcFile的文件写入outputStream中
popFile(srcFile, outputStream)) ;
} catch (IOException e) {
e.printStackTrace(); 
}
}

URLConnection con;
try {
//url是被调用的SERVLET的网址 如 *.do 
con = url.openConnection();
con.setUseCaches(false);
con.setDoInput(true);
con.setDoOutput(true);
con.setRequestProperty("Content-Type",
"application/octet-stream");
InputStream in = con.getInputStream();
ProgressMonitorInputStream pmInputStream = new ProgressMonitorInputStream
(pane, "正在从服务器下载文件内容", in);
ProgressMonitor pMonitor = pmInputStream.getProgressMonitor();
pMonitor.setMillisToDecideToPopup(3);
pMonitor.setMillisToPopup(3);
//localfilepath本地路径,localstr文件文件夹，filename本地文件名
String localfilepath = localstr + filename ;
//方法saveFilsaveFilee是把输入流pmInputStream写到文件localfilepath中 
if(saveFilsaveFilee(localfilepath,pmInputStream)){
　　　　 openLocalFile(localfilepath);
}

URLConnection con;
try {
con = url.openConnection();
//url是被调用的SERVLET的网址 如 *.do 
　　 con.setUseCaches(false);
con.setDoInput(true);
con.setDoOutput(true);
con.setRequestProperty("Content-Type","application/octet-stream"); 
OutputStream out = con.getOutputStream();
//localfilepath本地路径,localstr文件文件夹，filename本地文件名
String localfilepath = localstr + filename;
//文件getOutputStream是把文件localfilepath写到输出流out中
getOutputStream(localfilepath,out);
InputStream in = con.getInputStream();
return true;
}catch (IOException e) {
System.out.println("文件上传出错！");
e.printStackTrace();
}
servlet端代码示例 
public void service(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType(" text/plain ");
InputStream inputStream = null;
try {
inputStream = res.getInputStream();
//把输入流inputStream保存到文件路径为srcFile的文件中
writefile(srcFile, inputStream);
} catch (IOException e) {
e.printStackTrace();
}
} // end service