driver-async/src/main/com/mongodb/async/client/gridfs/helpers/AsyncStreamHelper.java
public static AsyncInputStream toAsyncInputStream(final InputStream inputStream) {
        notNull("inputStream", inputStream);
        return new AsyncInputStream() {
            @Override
            public void read(final ByteBuffer dstByteBuffer, final SingleResultCallback<Integer> callback) {
                notNull("dst", dstByteBuffer);
                notNull("callback", callback);
                if (!dstByteBuffer.hasRemaining()) {
                    callback.onResult(-1, null);
                    return;
                }

                int maxAmount = dstByteBuffer.remaining();
                byte[] bytes = new byte[maxAmount];
                int amountRead;
                try {
                    amountRead = inputStream.read(bytes);
                } catch (Throwable t) {
                    callback.onResult(null, new MongoGridFSException("Error reading from input stream", t));
                    return;
                }

                if (amountRead > 0) {
                    if (amountRead < maxAmount) {
                        byte[] dataRead = new byte[amountRead];
                        System.arraycopy(bytes, 0, dataRead, 0, amountRead);
                        dstByteBuffer.put(dataRead);
                    } else {
                        dstByteBuffer.put(bytes);
                    }
                }
                callback.onResult(amountRead, null);
            }

            @Override
            public void skip(final long bytesToSkip, final SingleResultCallback<Long> callback) {
                notNull("callback", callback);
                try {
                    long skipped = inputStream.skip(bytesToSkip);
                    callback.onResult(skipped, null);
                } catch (Throwable t) {
                    callback.onResult(null, t);
                }
            }

            @Override
            public void close(final SingleResultCallback<Void> callback) {
                try {
                    inputStream.close();
                } catch (Throwable t) {
                    callback.onResult(null, new MongoGridFSException("Error closing input stream", t));
                    return;
                }
                callback.onResult(null, null);
            }
        };
    }
public static AsyncInputStream toAsyncInputStream(final InputStream inputStream) {
        notNull("inputStream", inputStream);
        return new AsyncInputStream() {
            @Override
            public void read(final ByteBuffer dstByteBuffer, final SingleResultCallback<Integer> callback) {
                notNull("dst", dstByteBuffer);
                notNull("callback", callback);
                if (!dstByteBuffer.hasRemaining()) {
                    callback.onResult(-1, null);
                    return;
                }

                int maxAmount = dstByteBuffer.remaining();
                byte[] bytes = new byte[maxAmount];
                int amountRead;
                try {
                    amountRead = inputStream.read(bytes);
                } catch (Throwable t) {
                    callback.onResult(null, new MongoGridFSException("Error reading from input stream", t));
                    return;
                }

                if (amountRead > 0) {
                    if (amountRead < maxAmount) {
                        byte[] dataRead = new byte[amountRead];
                        System.arraycopy(bytes, 0, dataRead, 0, amountRead);
                        dstByteBuffer.put(dataRead);
                    } else {
                        dstByteBuffer.put(bytes);
                    }
                }
                callback.onResult(amountRead, null);
            }

            @Override
            public void skip(final long bytesToSkip, final SingleResultCallback<Long> callback) {
                notNull("callback", callback);
                try {
                    long skipped = inputStream.skip(bytesToSkip);
                    callback.onResult(skipped, null);
                } catch (Throwable t) {
                    callback.onResult(null, t);
                }
            }

            @Override
            public void close(final SingleResultCallback<Void> callback) {
                try {
                    inputStream.close();
                } catch (Throwable t) {
                    callback.onResult(null, new MongoGridFSException("Error closing input stream", t));
                    return;
                }
                callback.onResult(null, null);
            }
        };
    }
Converts a {@link InputStream} into a {@link AsyncInputStream}

@param inputStream the InputStream
@return the AsyncInputStream