２。在服务器端把文件转换成输出流，写入到response，以response把文件带到浏览器，由浏览器来提示用户是否愿意保存文件到本地。（示例如下）
<%
response.setContentType(fileminitype);
response.setHeader("Location",filename);
response.setHeader("Cache-Control", "max-age=" + cacheTime);
response.setHeader("Content-Disposition", "attachment; filename=" + filename); //filename应该是编码后的(utf-8)
response.setContentLength(filelength);
OutputStream outputStream = response.getOutputStream();
InputStream inputStream = new FileInputStream(filepath);
byte[] buffer = new byte[1024];
int i = -1;
while ((i = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, i);
}
outputStream.flush();
字串4
outputStream.close();
inputStream.close();
outputStream = null;
%>
３。既然是JSP的话，还有一种方式就是用Applet来实现文件的下载。不过客户首先得信任你的这个Applet小程序，由这个程序来接受由servlet发送来的数据流，并写入到本地。
servlet端示例
public void service(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType(" text/plain ");
OutputStream outputStream = null;
try {
outputStream = res.getOutputStream();
popFile(srcFile, outputStream)) ;//把文件路径为srcFile的文件写入到outputStream中。
} catch (IOException e) { 字串5
e.printStackTrace();
}
}
JApplet端示例
URLConnection con;
try {
con = url.openConnection();//url是被调用的SERVLET的网址 如http://localhost:8080/sendDateSevlet.do
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);
String localfilepath = localstr + filename ;//localfilepath本地路径,localstr文件文件夹，filename本地文件名
if(saveFilsaveFilee(localfilepath,pmInputStream)){ //方法saveFilsaveFilee是把输入流pmInputStream写到文件localfilepath中。 字串6
openLocalFile(localfilepath);
} 字串9
４。顺便把JApplet上传文件的代码也贴上来.
JApplet端示例
URLConnection con;
try {
con = url.openConnection();//url是被调用的SERVLET的网址 如http://localhost:8080/sendDateSevlet.do
con.setUseCaches(false);
con.setDoInput(true);
con.setDoOutput(true);
con.setRequestProperty("Content-Type",
"application/octet-stream");
OutputStream out = con.getOutputStream();
String localfilepath = localstr + filename; //localfilepath本地路径,localstr文件文件夹，filename本地文件名
字串4
getOutputStream(localfilepath,out);//文件getOutputStream是把文件localfilepath写到输出流out中。
InputStream in = con.getInputStream();
return true;
}catch (IOException e) {
System.out.println("文件上传出错！");
e.printStackTrace();
}
字串5
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();
writefile(srcFile, inputStream);//把输入流inputStream保存到文件路径为srcFile的文件中
} catch (IOException e) {
e.printStackTrace();
}
} // end service
字串9
字串5
总结：在文件的传输中是流的形式存在的，在硬盘上是文件的形式存在的。我们要做的只是通过HttpServletRequest和HttpServletResponse，或者是response和request来发送流和读取流。以及把文件转换成流或把流转换成文件的操作。
