JAVA：InputStream.read（byte [] b，int off，int len）中的字节数组分配

Question

I have a big file from which I want to get bytes divided in 20,000,000 bytes chunks.

I wrote a code like this:

File clipFile = new File("/home/adam/Temp/TheClip.mp4");
InputStream clipIStream = new FileInputStream(clipFile);

long chunkSize = 20000000;

long fileSize = clipFile.length();
long totalParts = (long) Math.ceil(fileSize / chunkSize);

for(int part=0; part < totalParts; part++) {
    long startOffset = chunkSize * part;
    byte[] bytes = new byte[(int)chunkSize];
    clipIStream.read(bytes, (int) startOffset, (int) chunkSize));

    // Code for processing the bytes array
    // ...
}

The program crashes after the first iteration, generating IndexOutOfBoundsException .

After consulting the documentation I found the following:

public int read(byte[] b, int off, int len) throws IOException

(...)

The first byte read is stored into element b[off], the next one into b[off+1], and so on.

It means, that on second iteration read begins writing on position bytes[20000000], instead of bytes[0] as I would want it.

Is there any way to achieve writing bytes on the beginning of the bytes array on every iteration?

Answer 1

Don't pass startOffset into the read method .

off - the start offset in array b at which the data is written.

The offset is into the array, not into the stream. Pass 0 instead, to write from the beginning of the array.