Android multi-threaded breakpoint download

Source code introduction

Implement multi-threaded breakpoint-resume download on Android, support pause and remember tasks.
Source code running screenshot

Source code snippet

 try {
                HttpURLConnection http = (HttpURLConnection) downUrl
                        .openConnection();
                http.setConnectTimeout( 5 * 1000 );
                http.setRequestMethod( "GET" );
                http.setRequestProperty( "Accept" , "image/gif, image/jpeg, image/pjpeg, image/pjpeg,application/x-shockwave-flash, application/xaml+xml,application/vnd.ms-xpsdocument, application/x-ms-xbap,application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword" );
 // http.setRequestProperty(, null); // Set the return data type that the client can accept   
                  
                http.setRequestProperty( "Accept-Language" , "zh-CN" );
 http.setRequestProperty( "Referer" , downUrl.toString()); // Set the source of the request to facilitate statistics on access sources  
                http.setRequestProperty( "Charset" , "UTF-8" ); 
  
 // Calculate the start position of the download thread  
 int startPos = block * (threadId - 1 ) + downloadedLength; 
                  
 /**
 * The end position of each block (the last block needs special treatment, because each block cannot be evenly distributed, and the last block may have a remainder)
 */  
 //int endPosition = (i + 1) != threadCount ? ((i + 1) * blockSize - 1): fileSize;  
 // Calculate the end position of the thread download  
 int endPos = threadId!=threadCount? (block *threadId):fileSize;
 // Set the range of entity data to be obtained. If the size of the entity data is exceeded, the actual data size will be automatically returned.  
                http.setRequestProperty( "Range" , "bytes=" + startPos + "-" + endPos);
 // Client user agent  
                http.setRequestProperty( "User-Agent" ,
 "Mozilla/4.0 (compatible; MSIE 8.0;"  
                                + "Windows NT 5.2; Trident/4.0;"  
                                + ".NET CLR 1.1.4322;"  
                                + ".NET CLR 2.0.50727;"  
                                + ".NET CLR 3.0.04506.30;"  
                                + ".NET CLR 3.0.4506.2152;"  
                                + " .NET CLR 3.5.30729)" ); 
  
 // Use long connection  
                http.setRequestProperty( "Connection" , "Keep-Alive" );
 // Get the input stream of the remote connection  
                InputStream inStream = http.getInputStream();
 // Set the size of the local data cache to 1M  
 byte [] buffer = new   byte [ 1024 ];
 // Set the amount of data to read each time  
 int offset = 0 ;
 // Print the location where the thread starts downloading  
                print( "Thread " + this .threadId
                        + " starts to download from position " + startPos);
                RandomAccessFile threadFile = new RandomAccessFile(
 this .saveFile, "rwd" );
 // The file pointer points to the location where the download starts  
                threadFile.seek(startPos);