List<HeapHistogramEntry> generateHeapHistogram() {
        final Object output = getRawHistogramOutput();

        final List<HeapHistogramEntry> heapHistogramEntries;
        if (output == null) {
            LOGGER.warn("Heap histogram produced no output for action {}", ACTION_NAME);
            heapHistogramEntries = Collections.emptyList();
        } else if (output instanceof String) {
            heapHistogramEntries = processOutput((String) output);
        } else {
            throw new RuntimeException(LogUtil.message("Unexpected type {}", output.getClass().getName()));
        }

        return heapHistogramEntries;
    }
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