@Override
    public void write(final String str, final int off, final int len) {
        sb.append(str.substring(off, off + len));
    }
Write a portion of a string.

@param str String to be written
@param off Offset from which to start writing characters
@param len Number of characters to write
stroom-pipeline/src/main/java/stroom/pipeline/writer/CharBufferWriter.java