java 判断网络位置文件是否存在 java获取网络文件

HttpURLConnection conn = null;
OutputStream outputStream = null;
InputStream inputStream = null;
try {
String path = r.getParameter("filename");
File fl = new File(path);
URL url = new URL(path);
conn = (HttpURLConnection)url.openConnection();
inputStream = conn.getInputStream();
rp.reset();
rp.setHeader("Content-Disposition", "attachment;filename=\""+ fl.getName() + "\"");
rp.setContentType("application/octet-stream");
rp.setContentLength((int)conn.getContentLength());
rp.setHeader("Pragma", "No-cache");
rp.setHeader("Cache-Control", "No-cache");
rp.setDateHeader("Expires", 0);
outputStream = new BufferedOutputStream(rp.getOutputStream());
byte[] buffer = new byte[4096];
int len = 0;
while((len = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, len);
}
outputStream.flush();
} catch(Exception e){
e.printStackTrace();
} finally {
if(conn!=null){
conn.disconnect();
}
if(inputStream != null) {
inputStream.close();
}
if(outputStream != null) {
outputStream.close();
}
}