read a File in hex byteArray and write part of that array to another File – java android

I have a 200kb file and I have to read it in bytes, and then write part of this byteArray (from index 90000 to 165000) to another file. How can I accomplish this.

File file1 = new File(getExternalStorageDirectory(), "file1.raw"); //the 200kb file
try {
         File.createTempFile("file2", "mp3", getCacheDir()); //empty file that needs to get filled with part of the byte array from file1
        } catch (IOException ignored) {}

Answer

Use a RandomAccessFile in order to seek to the offset to start copying from.

For example:

final int bufSize = 1024; // the buffer size for copying
byte[] buf = new byte[bufSize];

final long start = 10000L; // start offset at source
final long end = 15000L;   // end (non-inclusive) offset at source
try (
    RandomAccessFile in = new RandomAccessFile("input.bin", "r");
    OutputStream out = new FileOutputStream("output.bin")) 
{
      in.seek(start);
      long remaining = end - start;
      do {
         int n = (remaining < bufSize)? ((int) remaining) : bufSize;
         int nread = in.read(buf, 0, n);
         if (nread < 0)
             break; // EOF
         remaining -= nread;
         out.write(buf, 0, nread);
      } while (remaining > 0);
}