private static String getTruncatedStr(final String str) {
        if (str != null && str.length() > STRING_TRUNCATE_LIMIT) {
            return str.substring(0, STRING_TRUNCATE_LIMIT) + "...TRUNCATED...";
        } else {
            return str;
        }
    }
Generates a heap histogram using the 'gcClassHistogram' MBean action.  Will
block until the action completes/fails.
list of {@link HeapHistogramEntry}
stroom-node/stroom-node-impl/src/main/java/stroom/node/impl/HeapHistogramService.java