Question

I wanted to get some advice, I have started on a new project to create a java download accelerator that will use multiple connections. I wanted to know how best to go about this.

So far I have figured out that i can use HttpUrlConnection and use the range property, but wanted to know an efficient way of doing this. Once i have download the parts from the multiple connections i will then have to join the parts so that we end up with a fully downloaded file.

Thanks in advance 🙂

Answer 1

1. Get the content length of the file to download.
2. Divide it according to a criteria (size, speed, …).
3. Run multiple threads to download the file starting at different positions,
   and save them in different files: myfile.part1,  myfile.part2, …
4. Once downloaded, join the parts into one single file.

I tried the following code to get the content length:

public Downloader(String path) throws IOException {
    int len = 0;
    URL url = new URL(path);
    URLConnection connectUrl = url.openConnection();
    System.out.println(len = connectUrl.getContentLength());
    System.out.println(connectUrl.getContentType());

    InputStream input = connectUrl.getInputStream();
    int i = len;
    int c = 0;
    System.out.println("=== Content ==="); 
    while (((c = input.read()) != -1) && (--i > 0)) {
        System.out.print((char) c);
    }
    input.close(); 
}

Here’s a sample code to join the files:

public void join(String FilePath) {
    long leninfile=0, leng=0;
    int count=1, data=0;
    try {
        File filename = new File(FilePath);
        RandomAccessFile outfile = new RandomAccessFile(filename,"rw");
        while(true) {
            filename = new File(FilePath + count + ".sp");
            if (filename.exists()) {
                RandomAccessFile infile = new RandomAccessFile(filename,"r");
                data=infile.read();
                while(data != -1) {
                    outfile.write(data);
                    data=infile.read();
                }
                leng++;
                infile.close();
                count++;
            } else break;
        }
        outfile.close();
    } catch(Exception e) {
        e.printStackTrace();
    }
}