@Override
    public void addRequestContentLength(long contentLength) {
        if (contentLength < 0)
            throw new IllegalArgumentException();
        synchronized(lock) {
            if (this.requestContentLength == -1)
                this.requestContentLength = contentLength;
            else
                this.requestContentLength += contentLength;
        }
    }
Adds the number of bytes to be expected in the request.
aws-java-sdk-core/src/main/java/com/amazonaws/event/request/ProgressSupport.java