Exploring NLP Concepts Using Apache OpenNLP

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Exploring NLP Concepts Using Apache OpenNLP

In this article, we take a look at Apachce NLP, including basic functionality, tokenization, POS Tagging, its CLI, and java Bindings.

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After looking at a lot of Java/JVM based NLP libraries listed on Awesome AI/ML/DL, I decided to pick the Apache OpenNLP library. One of the reasons comes from the fact that another developer (who had a look at it previously) recommended it. Besides, it’s an Apache project; they have been great supporters of F/OSS Java projects for the last two decades or so (see Wikipedia). It also goes without saying that Apache OpenNLP is backed by the Apache 2.0 license.

In addition, this tweet from an NLP researcher added some more confidence to my choice:

Tweet on OpenNLP

I’ll like to say my personal experience has been similar with Apache OpenNLP so far, and I echo the simplicity and user-friendly API and design.

You may also like: A Guide to Natural Language Processing (Part 1).

Exploring NLP Using Apache OpenNLP

Java Bindings

We won’t be covering the Java API to Apache OpenNLP tool in this post, but you can find a number of examples in their docs. A bit later, you will also need some of the resources enlisted in the Resources section at the bottom of this post in order to progress further.

Command Line Interface

I was drawn to the simplicity of the CLI available, and it just worked out-of-the-box — for instance, where a model was needed, and when it was provided. It would just work without additional configuration.

To make it easier to use and also not have to remember all the CLI parameters it supports, I have put together some shell scripts. Have a look at the README to get more insight into what they are and how to use them.

Getting Started

You will need the following from this point forward:

  • Git client 2.x or higher (an account on GitHub to fork the repo).
  • Java 8 or higher (suggest install GraalVM CE 19.x or higher).
  • Docker CE 19.x or higher and check it is running before going further.
  • Ability to run shell scripts from the CLI.
  • Understand reading/writing shell scripts (optional).

Note: At the time of the writing, version 1.9.1 of Apache OpenNLP was available.

We have put together scripts to make these steps easy for everyone:

$ git clone git@github.com:valohai/nlp-java-jvm-example.git
$ git clone https://github.com/valohai/nlp-java-jvm-example.git
$ cd nlp-java-jvm-example

This will lead us to the folder with the following files in it:

docker-runner.sh     <=== only this one concerns us at startup
shared               <=== created just when you run the container

Note: docker image has been provided to be able to run a docker container that would contain all the tools you need to go further. You can see the *shared* folder has been created, which is a volume mounted into your container, but it’s actually a directory created on your local machine and mapped to this volume. So, anything created or downloaded there will be available even after you exit out of your container!

Have a quick read of the main README file to get an idea of how to go about using the docker-runner.sh shell script, and take a quick glance at the Usage section as well. Also take a look into the Apache OpenNLP README file to see the usages of the scripts provided.

Run the NLP Java/JVM Docker Container

At your local machine command prompt while at the root of the project, do this:

$ ./docker-runner.sh --runContainer

There is a chance you get this before you get the prompt:

Unable to find image 'neomatrix369/nlp-java:0.1' locally
0.1: Pulling from neomatrix369/nlp-java
f476d66f5408: ...
Digest: sha256:53b89b166d42ddfba808575731f0a7a02f06d7c47ee2bd3622e980540233dcff
Status: Downloaded newer image for neomatrix369/nlp-java:0.1

Thenm you will be presented with prompt inside the container:

Running container neomatrix369/nlp-java:0.1

++ pwd
+ time docker run --rm --interactive --tty --workdir /home/nlp-java --env JDK_TO_USE= --env JAVA_OPTS= --volume /Users/swami/git-repos/awesome-ai-ml-dl/examples/nlp-java-jvm/shared:/home/nlp-java/shared neomatrix369/nlp-java:0.1

The container is packed with all the Apache OpenNLP scripts/tools you need to get started with exploring various NLP solutions.

Installing Apache OpenNLP Inside the Container

Here is how we go further from here when you are inside the container, at the container command-prompt:

nlp-java@cf9d493f0722:~$ cd opennlp

nlp-java@cf9d493f0722:~$ ./opennlp.sh

You will see the apache-opennlp-1.9.1-bin.tar.gz artifact being downloaded and expanded into the shared folder:

% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 10.6M  100 10.6M    0     0  4225k      0  0:00:02  0:00:02 --:--:-- 4225k

Viewing and Accessing the Shared Folder

Just as you run the container, a shared folder is created; it may be empty in the beginning, but as we go along, we will find it fill up with different files and folders.

It’s also where you will find the downloaded models and the Apache OpenNLP binary exploded into its own directory (by the name apache-opennlp-1.9.1).

You can access and see the contents of it from the command-prompt (outside the container) as well. From inside the container, this is what you see:

nlp-java@cf9d493f0722:~$ ls 
cogcomp-nlp.sh   corenlp.sh  nlp4j.sh  openregex.sh        reverb.sh  word2vec.sh
common.sh        mallet.sh   opennlp   rdrposttagger.sh        shared

nlp-java@cf9d493f0722:~$ ls shared
MyFirstJavaNotebook.ipynb      en-ner-date.bin           en-pos-maxent.bin          
apache-opennlp-1.9.1           en-ner-time.bin           en-pos-perceptron.bin  
en-chunker.bin                 en-parser-chunking.bin    en-token.bin

### In your case the contents of the shared folder may vary but the way to get to the folder is above.

Performing NLP Actions Inside the Container

The good thing is without ever leaving your current folder, you can perform these NLP actions (check out the Exploring NLP Concepts section in the README):

Usage help of any of the scripts: at any point in time you can always query the scripts by calling them this way:

 nlp-java@cf9d493f0722:~$ ./[script-name.sh] --help

For e.g.

nlp-java@cf9d493f0722:~$ ./detectLanguage.sh --help

gives us this usage text as output:

 Detecting language in a single line text or article

       Usage: ./detectLanguage.sh --text [text]
                 --file [path/to/filename]

       --text      plain text surrounded by quotes
       --file      name of the file containing text to pass as command arg
       --help      shows the script usage help text

Detecting language in a single line text or article (see legend of language abbreviations used)

nlp-java@cf9d493f0722:~$ ./detectLanguage.sh --text "This is an english sentence"

eng This is an english sentence

See the Detecting languages section in the README for more examples and detailed output. Detecting sentences in a single line text or article.

./detectSentence.sh --text "This is an english sentence. And this is another sentence."

This is an english sentence.
And this is another sentence.

See the Detecting sentences section in the README for more examples and detailed output.

Finding a person's name, organization name, date, time, money, location, percentage information in a single line text or article.

nlp-java@cf9d493f0722:~$ ./nameFinder.sh --method person  --text "My name is John"

My name is <START:person> John <END>

See the Finding names section in the README for more examples and detailed output. There are a number of types of name finder examples in this section.

Tokenize a line of text or an article into its smaller components (i.e. words, punctuation, numbers).

nlp-java@cf9d493f0722:~$ ./tokenizer.sh --method simple --text "this-is-worth,tokenising.and,this,is,another,one"

this - is - worth , tokenising . and , this , is , another , one

See the Tokenize section in the README for more examples and detailed output.

Parse a line of text or an article and identify groups of words or phrases that go together (see Penn Treebank tag set for legend of token types). Also see https://nlp.stanford.edu/software/lex-parser.shtml.

nlp-java@cf9d493f0722:~$ ./parser.sh --text "The quick brown fox jumps over the lazy dog ."

(TOP (NP (NP (DT The) (JJ quick) (JJ brown) (NN fox) (NNS jumps)) (PP (IN over) (NP (DT the) (JJ lazy) (NN dog))) (. .)))

See the Parser section in the README for more examples and detailed output.

Tag parts of speech of each token in a line of text or an article (see Penn Treebank tag set for legend of token types). Also see https://nlp.stanford.edu/software/tagger.shtml.

nlp-java@cf9d493f0722:~$ ./posTagger.sh --method maxent --text "This is a simple text to tag"

This_DT is_VBZ a_DT simple_JJ text_NN to_TO tag_NN

See the Tag Parts of Speech section in the README for more examples and detailed output.

Text chunking by dividing a text or an article into syntactically correlated parts of words, like noun groups, verb groups. You apply this feature to the tagged parts of speech text or article. Apply chunking on a text already tagged by PoS tagger (see Penn Treebank tag set for legend of token types, also see https://nlpforhackers.io/text-chunking/)

nlp-java@cf9d493f0722:~$ ./chunker.sh --text "This_DT is_VBZ a_DT simple_JJ text_NN to_TO tag_NN

 [NP This_DT ] [VP is_VBZ ] [NP a_DT simple_JJ text_NN ] [PP to_TO ] [NP tag_NN]

See Chunking section in the README for more examples and detailed output.

Exiting From the NLP Java/JVM Docker Container

It is as simple as this:

nlp-java@f8562baf983d:~/opennlp$ exit
       67.41 real         0.06 user         0.05 sys

And you are back to your local machine prompt.


One of the salient features of this tool is its recording and reporting metrics of its actions at different execution points — time taken at micro and macro levels. here’s a sample output to illustrate this feature:

Loading Token Name Finder model ... done (1.200s)
My name is <START:person> John <END>

Average: 24.4 sent/s
Total: 1 sent
Runtime: 0.041s
Execution time: 1.845 seconds

From the above code block, I have come across five metrics that are useful for me as a scientist, analyst, or even as an engineer:

Took 1.200s to load the model into memory

(Average) Processed at an average rate of 24.4 sentences per second
(Total) Processed 1 sentence
(Runtime) It took 0.040983606557377 (0.041 seconds) to process this 1 sentence
(Execution time) The whole process ran for 1.845 seconds (startup, processing sentence(s) and shutdown)

Information like this is invaluable when it comes to making performance comparisons:

  • Between two or more models (load-time and run-time performance)
  • Between two or more environments or configurations
  • Between applications doing the same NLP action put together using different tech stacks
    • Including different languages
  • Finding correlations between different corpuses of text data processed (quantitative and qualitative comparisons)

Empirical Example

BetterNLP library written in python is doing something similar. See Kaggle kernels: Better NLP Notebook and Better NLP Summarisers Notebook. (search fortime_in_secsinside inboth the notebooks to see the metrics reported.)

(look for …&lt;em&gt;time&lt;/em&gt;in&lt;em&gt;secs = …)(look for …&lt;/em&gt;time&lt;em&gt;in&lt;/em&gt;secs = …)

Personally, it’s quite inspiring and also validating that this is a useful feature (or action) to offer to the end-user.

Other Concepts, Libraries, and Tools

There are other Java/JVM based NLP libraries mentioned in the Resources section below. For brevity, we won’t cover them. The links provided will lead to further information for your own pursuit.

Within the Apache OpenNLP tool itself, we have only covered the command line access part of it and not the Java Bindings. In addition, we haven’t gone through all the NLP concepts or features of the tool again for brevity that have only covered a handful of them. But the documentation and resources on the GitHub repo should help in further exploration.

You can also find out how to build the docker image for yourself by examining the docker-runner script.


Image title

After going through the above, we can conclude the following about the Apache OpenNLP tool by exploring its pros and cons:


  • It’s an easy to use API and understand
  • Shallow learning curve and detailed documentation with lots of examples
  • Covers a lot of NLP functionality, there’s more in the docs to explore than we did above
  • Easy shell scripts and Apache OpenNLP scripts have been provided to play with the tool
  • Lots of resources available below to learn more about NLP (See the Resources section below)
  • Resources provided to quickly get started and explore the Apache OpenNLP tool


  • Looking at the GitHub repo, it seems the development is slow or has been stagnated (last two commits have a wide gap i.e. May 2019 and Oct 15, 2019)
  • A few models are missing when going through the examples in the documentation (manual)
  • The current models provided may need further training as per your use case(s), see this tweet:

Image title


Apache OpenNLP

Further Reading

apache opennlp ,big dat ,deep learning ,docker ,java ,nlp ,nltk ,text mining ,text processing

Published at DZone with permission of Mani Sarkar . See the original article here.

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