从ByteArrayOutputStream修剪填充

Question

I'm working with Amazon S3 and would like to upload an InputStream (which requires counting the number of bytes I'm sending).

public static boolean uploadDataTo(String bucketName, String key, String fileName, InputStream stream) {

    ByteArrayOutputStream out = new ByteArrayOutputStream();
    byte[] buffer = new byte[1];

    try {
        while (stream.read(buffer) != -1) { // copy from stream to buffer
            out.write(buffer); // copy from buffer to byte array
        }
    } catch (Exception e) {
        UtilityFunctionsObject.writeLogException(null, e);
    }

    byte[] result = out.toByteArray(); // we needed all that just for length
    int bytes = result.length;
    IO.close(out);
    InputStream uploadStream = new ByteArrayInputStream(result);

    ....

}

I was told copying a byte at a time is highly inefficient (obvious for large files). I can't make it more because it will add padding to the ByteArrayOutputStream , which I can't strip out. I can strip it out from result , but how can I do it safely? If I use an 8KB buffer, can I just strip out the right most buffer[i] == 0 ? Or is there a better way to do this? Thanks!

Using Java 7 on Windows 7 x64.

Answer 1

You can do something like this:

int read = 0;
while ((read = stream.read(buffer)) != -1) {
    out.write(buffer, 0, read);
}

stream.read() returns the number of bytes that have been written into buffer . You can pass this information to the len parameter of out.write() . So you make sure that you write only the bytes you have read from the stream.

Answer 2

Use Jakarta Commons IOUtils to copy from the input stream to the byte array stream in a single step. It will use an efficient buffer, and not write any excess bytes.

Answer 3

If you want efficiency you could process the file as you read it. I would replace uploadStream with stream and remove the rest of the code.

If you need some buffering you can do this

 InputStream uploadStream = new BufferedInputStream(stream);

the default buffer size is 8 KB.

If you want the length use File.length();

 long length = new File(fileName).length();