alex.mojaki.s3upload.ConvertibleOutputStream Maven / Gradle / Ivy

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Manages streaming of data to S3 without knowing the size beforehand and without keeping it all in memory or writing to disk.

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package alex.mojaki.s3upload;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.*;

/**
 * A ByteArrayOutputStream with some useful additional functionality.
 */
class ConvertibleOutputStream extends ByteArrayOutputStream {

    private static final Logger log = LoggerFactory.getLogger(ConvertibleOutputStream.class);

    public ConvertibleOutputStream(int initialCapacity) {
        super(initialCapacity);
    }

    /**
     * Creates an InputStream sharing the same underlying byte array, reducing memory usage and copying time.
     */
    public InputStream toInputStream(){
        return new ByteArrayInputStream(buf, 0, count);
    }

    /**
     * Truncates this stream to a given size and returns a new stream containing a copy of the remaining data.
     *
     * @param countToKeep number of bytes to keep in this stream, starting from the first written byte.
     * @param initialCapacityForNewStream buffer capacity to construct the new stream (NOT the number of bytes
     *                                    that the new stream will take from this one)
     * @return a new stream containing all the bytes previously contained in this one, i.e. from countToKeep + 1 onwards.
     */
    public ConvertibleOutputStream split(int countToKeep, int initialCapacityForNewStream) {
        int newCount = count - countToKeep;
        log.debug("Splitting stream of size {} into parts with sizes {} and {}", count, countToKeep, newCount);
        initialCapacityForNewStream = Math.max(initialCapacityForNewStream, newCount);
        ConvertibleOutputStream newStream = new ConvertibleOutputStream(initialCapacityForNewStream);
        newStream.write(buf, countToKeep, newCount);
        count = countToKeep;
        return newStream;
    }

    /**
     * Concatenates the given stream to this stream.
     */
    public void append(ConvertibleOutputStream otherStream) {
        try {
            otherStream.writeTo(this);
        } catch (IOException e) {

            // Should never happen because these are all ByteArrayOutputStreams
            throw new AssertionError(e);
        }
    }
}