Java通过URL下载网络文件，获取文件流并修改文件名

function downloadAttachement(imageId,fileName){
var url = _HTTP_IP_PORT +'repayment/downloadAttachment.do?imageId='+ imageId +'&fileName='+fileName;
var form = $("<form></form>").attr("action", url).attr("method", "post");
form.appendTo('body').submit().remove();
}

@RequestMapping(value = "/repayment/downloadAttachment", method = RequestMethod.POST)
@ResponseBody
public String downloadAttachment(String imageId,String fileName,HttpServletRequest request,HttpServletResponse response) {
if (StringUtils.isEmpty(imageId)) {
throw new CommonException("影像ID不能为空！");
}
if (StringUtils.isEmpty(fileName)) {
throw new CommonException("文件名不能为空！");
}
//这里获取的下载链接 http://sk.sit.fosuntech.cn/group1/M00/00/72/CqYKHVn69wyAMl6YAAVf953sp4Y075.pdf String downLoadPath = templateService.getDownloanUrl(imageId);
BufferedInputStream bis = null;
BufferedOutputStream bos = null;
try {

//如果不存在乱码的情况可以忽略，由于请求参数文件名为中文，到后台会乱码，考虑操作系统和客户端浏览器默认编码
//判断服务器操作系统，本地开发使用windows
String os = System.getProperty("os.name");
if(os.toLowerCase().indexOf("windows") != -1){
fileName = new String(fileName.getBytes("GBK"), "ISO-8859-1");
}else{
//判断浏览器
String userAgent = request.getHeader("User-Agent").toLowerCase();
if(userAgent.indexOf("msie") > 0){
fileName = URLEncoder.encode(fileName, "ISO-8859-1");
}
}
//响应二进制流
response.setContentType("application/octet-stream");
response.reset();//清除response中的缓存
//根据网络文件地址创建URL
URL url = new URL(downLoadPath);
//获取此路径的连接
URLConnection conn = url.openConnection();
Long fileLength = conn.getContentLengthLong();//获取文件大小
//设置reponse响应头，真实文件名重命名，就是在这里设置，设置编码
response.setHeader("Content-Disposition",
"attachment; filename=" + fileName);
response.setHeader("Content-Length", String.valueOf(fileLength));

bis = new BufferedInputStream(conn.getInputStream());//构造读取流
bos = new BufferedOutputStream(response.getOutputStream());//构造输出流
byte[] buff = new byte[1024];
int bytesRead;
//每次读取缓存大小的流，写到输出流
while (-1 != (bytesRead = bis.read(buff, 0, buff.length))) {
bos.write(buff, 0, bytesRead);
}
response.flushBuffer();//将所有的读取的流返回给客户端
} catch (IOException e) {
logger.error("文件下载失败！", e);
throw new CommonException("文件下载失败！");
}finally{
try{
if(null != bis){
bis.close();
}
if(null != bos){
bos.close();
}
}catch(IOException e){
logger.error("文件下载失败！", e);
throw new CommonException("文件下载失败！");
}
}
return null;
}