Read a segment of a file in Java / Android

Question

I\'m sure this might be a simple question, but unfortunately this is my first time using Java and working the Android SDK.

I am uploading files on Android using the

Answer 1

I was able to figure it out... just had to discover that there's a ByteArrayInputStream that would allow me to convert my byte[] buffer to an InputStream. From here on, I can now track which chunks failed and handle it. Thanks Konstantin for Here's my implementation:

    final int chunkSize = 512 * 1024; // 512 kB
    final long pieces = file.length() / chunkSize;
    int chunkId = 0;

    HttpPost request = new HttpPost(endpoint);

    BufferedInputStream stream = new BufferedInputStream(new FileInputStream(file));

    for (chunkId = 0; chunkId < pieces; chunkId++) {
        byte[] buffer = new byte[chunkSize];

        stream.skip(chunkId * chunkSize);
        stream.read(buffer);

        MultipartEntity entity = new MultipartEntity();
        entity.addPart("chunk_id", new StringBody(String.valueOf(chunkId)));
        request.setEntity(entity);
        ByteArrayInputStream arrayStream = new ByteArrayInputStream(buffer);

        entity.addPart("file_data", new InputStreamBody(arrayStream, filename));

        HttpClient client = app.getHttpClient();
        client.execute(request);
    }

Answer 2

Use skip() method of FileInputStream stream to seek to the fragment you need.

Answer 3

You can either use the skip(long) method to skip the number of bytes in the InputStream or you can create a RandomAccessFile on the File object and call its seek(long) method to set the pointer to that position so you can start reading from there.

The quick test below reads in a 4mb+ file (between 3m and 4mb) and writes the read data to an ".out" file.

import java.io.*;
import java.util.*;

public class Test {

    public static void main(String[] args) throws Throwable {
       long threeMb = 1024 * 1024 * 3;
       File assembled =  new File(args[0]); // your downloaded and assembled file
       RandomAccessFile raf = new RandomAccessFile(assembled, "r"); // read
       raf.seek(threeMb); // set the file pointer to 3mb
       int bytesRead = 0;
       int totalRead = 0;
       int bytesToRead = 1024 * 1024; // 1MB (between 3M and 4M

       File f = new File(args[0] + ".out");
       FileOutputStream out = new FileOutputStream(f);

       byte[] buffer = new byte[1024 * 128]; // 128k buffer 
       while(totalRead < bytesToRead) { // go on reading while total bytes read is
                                        // less than 1mb
         bytesRead = raf.read(buffer);
         totalRead += bytesRead;
         out.write(buffer, 0, bytesRead);
         System.out.println((totalRead / 1024));
       }
    }
}