public static File downLoad(String serverPath,String savedPath,ProgressDialog dialog){  
            try {  
                  
                URL url=new URL(serverPath);  
                HttpURLConnection _conn=(HttpURLConnection) url.openConnection();  
                _conn.setRequestMethod("GET");  
                _conn.setConnectTimeout(5000);  
                int code=_conn.getResponseCode();  
                if(code==200){  
                    //设置进度条的长度  
                    dialog.setMax(_conn.getContentLength());  
                    InputStream is=_conn.getInputStream();  
                    File _file=new File(savedPath);  
                    FileOutputStream _FileOutputStream=new FileOutputStream(_file);  
                    int len=0;  
                    byte[] buffer= new byte[1024];  
                    int _total=0;  
                    while((len=is.read(buffer))!=-1){  
                        _FileOutputStream.write(buffer, 0,len);  
                        _total+=len;  
                        dialog.setProgress(_total);  
                        Thread.sleep(20);  
                    }  
                    _FileOutputStream.flush();  
                    _FileOutputStream.close();  
                    is.close();  
                    return _file;  
                }else {  
                    return null;  
                }  
            } catch (Exception e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
                return null;  
            }  
              
              
        }