Text Summarization is a frequently asked for feature that's presently lacking in OpenNLP. There has been recent work on Text Summarization using Deep Learning techniques like.
See Blog by Abigail See; and the paper Get to the Point: Summarization with Pointer Generator Networks by Abigail See, Christopher Manning, Peter J. Liu.
Previous work on Summarization is available at https://github.com/apache/opennlp-sandbox/tree/master/summarizer/src/main/java/opennlp/summarization
With recent advances in Deep Learning techniques, the whole field of NLP is now being treated anew using Deep Learning techniques.
References:
https://arxiv.org/abs/1801.10198