What is Sentence Detection

Sentence Detection or Sentence Segmentation is a process of finding the start and end of a sentence (in a paragraph). This has to be done often in pre-processing section of most of the use cases, which are trying to be solved using Natural Language Processing techniques. Furthermore, Sentence Detection is one of the problems in Natural Language Processing.

Sentence detection is quite challenging because of many reasons in which one of them is : Period symbol (.) which usually denotes the end of a sentence, could also come in an email addresses, abbreviations, decimals etc.,

Sentence Detection Example in OpenNLP

The following example, SentenceDetectExample.java shows how to use SentenceDetectorME class to detect sentences in a paragraph/string. If you would like to know how to setup eclipse project, refer to setup of java project with openNLP libraries, in eclipse. The process should be same, even for a different IDE(adding the required jars to the build path should do the magic).


import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import com.fasterxml.jackson.databind.exc.InvalidFormatException;

import opennlp.tools.sentdetect.SentenceDetectorME;
import opennlp.tools.sentdetect.SentenceModel;

 * Sentence Detection Example in openNLP using Java
 * @author tutorialkart
public class SentenceDetectExample {

	public static void main(String[] args) {
		try {
			new SentenceDetectExample().sentenceDetect();
		} catch (IOException e) {

	 * This method is used to detect sentences in a paragraph/string
	 * @throws InvalidFormatException
	 * @throws IOException
	public void sentenceDetect() throws InvalidFormatException,	IOException {
		String paragraph = "This is a statement. This is another statement. Now is an abstract word for time, that is always flying.";

		// refer to model file "en-sent,bin", available at link http://opennlp.sourceforge.net/models-1.5/
		InputStream is = new FileInputStream("en-sent.bin");
		SentenceModel model = new SentenceModel(is);
		// feed the model to SentenceDetectorME class 
		SentenceDetectorME sdetector = new SentenceDetectorME(model);
		// detect sentences in the paragraph
		String sentences[] = sdetector.sentDetect(paragraph);

		// print the sentences detected, to console
		for(int i=0;i<sentences.length;i++){

When SentenceDetectExample,java is run, the console output is as shown in the following.

This is a statement.
This is another statement.
Now is an abstract word for time, that is always flying.

The project structure and model file location, etc., for the example is shown below:

Sentence Detection Example in openNLP - example project structure - Tutorialkart
Example Project – Structure

Model File

The model file en-sent.bin is available at [http://opennlp.sourceforge.net/models-1.5/]. Stay updated regarding latest releases of openNLP or model files, at [https://opennlp.apache.org/download.html]

Java Documentation

Find the java documentation for SentenceDetectorME at official site and play with the other methods like getSentenceProbabilities(), sentPosDetect(String s), etc., for a better understanding.

Custom model for Sentence Detection from user defined training data

If you are interested in knowing of how to train and generate a model yourself for Sentence Detection, refer to training a model for Sentence Detection in openNLP.


In this Apache OpenNLP Tutorial, we have seen Sentence Detection Example in OpenNLP using Java.