Question

好吧，我正在开发一个应用程序，它将读取用户输入的URL并使用openConnection()方法等下载特定文件。我有一个功能，用户可以选择远程连接的数量。我做了两次测试。首先是1个连接，第二个测试是4个连接。问题是1连接下载的字节与文件的总字节数相同，但是当我尝试使用4连接时，下载的字节总是大于总字节数。因此，当我打开下载的文件时，它看起来已损坏。这是我的代码：

以下是来自DownloadFile.java

的代码

SubDownload sd[];
int DownloadID=1, ActiveSubConn=0, BufferSize=1;
long FileSize = 9301;    //bytes
int TotConnections=1;    //by Default '1' for first testing and '4' for second testing
long ld_FStartPos, ld_FEndPos, ld_partsize;
String partname;
String FileLoc = "http://static.webshopapp.com/shops/010317/files/002503512/140x140x2/13-m-kite-refit-service.jpg";

public int StartDownload()
{ 
    sd = new SubDownload[TotConnections];
    ld_partsize= (long)(FileSize/TotConnections);
            System.out.println("FileSize: "+FileSize);

    for (li_conn=0;li_conn < TotConnections ;li_conn++)
    {
        if ( li_conn == (TotConnections - 1))
        {
            ld_FStartPos=li_conn*ld_partsize;
            ld_FEndPos= FileSize;
        }
        else
        {
            ld_FStartPos=li_conn*ld_partsize;
            ld_FEndPos= ld_FStartPos + ld_partsize - 1;
        }

        partname = "DFL" +  String.valueOf(DownloadID) + String.valueOf(li_conn) + ".txt";
        sd[li_conn] = new SubDownload(partname, FileLoc, ld_FStartPos, ld_FEndPos, BufferSize);
        sd[li_conn].start();
        ActiveSubConn = ActiveSubConn + 1;
    }
    return li_conn;          
}

以下是来自SubDownload.java

的代码

public  String SubDownloadId, FileLoc;
public  long FileStartPos, FileEndPos, BytesDownloaded=0;
public  byte Buffer[];

public SubDownload(String aSubDownloadId,String aFileLoc,long aFileStartPos,
                long aFileEndPos,int aBufferSize){

    FileLoc=aFileLoc;
    FileStartPos=aFileStartPos;
    FileEndPos=aFileEndPos;
    Buffer = new byte[1024 * aBufferSize];  
    BytesDownloaded=0;
    SubDownloadId=aSubDownloadId;
}

public void run(){
    try{
        URL url = new URL(FileLoc);
        URLConnection uc = url.openConnection();
        BufferedInputStream instream;
        uc.setRequestProperty("Range","bytes=" + FileStartPos + "-"+ FileEndPos);

        instream = new BufferedInputStream(uc.getInputStream());

        int li_bytesRead;
        File f = new File(SubDownloadId);
        RandomAccessFile raf = new RandomAccessFile(f, "rw");

        while(BytesDownloaded < (FileEndPos - FileStartPos))
        {
            if (status ==1)
            {
                if(BytesDownloaded==0) System.out.println("Start: "+FileStartPos+" End: "+FileEndPos);
                li_bytesRead = instream.read(Buffer);
                raf.write(Buffer,0,li_bytesRead);
                BytesDownloaded = BytesDownloaded + li_bytesRead;
                System.out.println("Bytes Read: "+li_bytesRead+" TotalBytesRead: "+BytesDownloaded);
             }
        }

    }catch(Exception e){}


    }

现在是测试部分。在第一个测试中，我设置了TotConnections=1;并开始下载。这是打印在控制台中的结果。

FileSize: 9301 Start: 0 End: 9301 Bytes Read: 1024 TotalBytesRead: 1024 Bytes Read: 1024 TotalBytesRead: 2048 Bytes Read: 1024 TotalBytesRead: 3072 Bytes Read: 1024 TotalBytesRead: 4096 Bytes Read: 1024 TotalBytesRead: 5120 Bytes Read: 1024 TotalBytesRead: 6144 Bytes Read: 1024 TotalBytesRead: 7168 Bytes Read: 1024 TotalBytesRead: 8192 Bytes Read: 1024 TotalBytesRead: 9216 Bytes Read: 85 TotalBytesRead: 9301

当我打开下载的文件时，它已成功打开，没有发生错误或损坏。接下来在第二次测试中我设置了TotConnections=4;并开始了。结果：

FileSize: 9301 Start: 4650 End: 6974 Bytes Read: 1024 TotalBytesRead: 1024 Bytes Read: 22 TotalBytesRead: 1046 Bytes Read: 1024 TotalBytesRead: 2070 Bytes Read: 1024 TotalBytesRead: 3094 Start: 6975 End: 9301 Bytes Read: 1024 TotalBytesRead: 1024 Bytes Read: 1024 TotalBytesRead: 2048 Bytes Read: 1024 TotalBytesRead: 3072 Start: 0 End: 2324 Bytes Read: 1024 TotalBytesRead: 1024 Bytes Read: 1024 TotalBytesRead: 2048 Bytes Read: 1024 TotalBytesRead: 3072 Start: 2325 End: 4649 Bytes Read: 1024 TotalBytesRead: 1024 Bytes Read: 1024 TotalBytesRead: 2048 Bytes Read: 1024 TotalBytesRead: 3072

如果现在我打开下载的文件，它将无法正常打开。该文件已损坏。总之，第一次测试中的TotalBytesRead为9301字节，而第二次测试中为12310字节。

如果我将TotConnections设置为1，则除了1之外没有任何问题导致问题。有人能告诉我，我做的错误是什么？请给我一个解决方案。

**更正：有时只下载使用4个或更多1个连接下载的文件而不会损坏，否则大多数情况下文件仅被破坏。

下载的字节数略高于文件的总字节数 - Java

0 个答案: