W.S. W.S. - 1 month ago 10x
Python Question

corenlp sentiment Java program via Py4j in Python, raises errors

I made a Java sentiment analysis program to be used in Python via Py4j. I can create the Java object in Python, but try to access the method, it gives java.lang.NullPointerException. Could you help please? Thanks.

Java code: it compiles correctly, runs without errors.

import java.util.List;
import java.util.Properties;
import edu.stanford.nlp.ling.CoreAnnotations;
import edu.stanford.nlp.neural.rnn.RNNCoreAnnotations;
import edu.stanford.nlp.pipeline.Annotation;
import edu.stanford.nlp.pipeline.StanfordCoreNLP;
import edu.stanford.nlp.sentiment.SentimentCoreAnnotations.SentimentAnnotatedTree;
import edu.stanford.nlp.trees.Tree;
import edu.stanford.nlp.util.ArrayCoreMap;
import edu.stanford.nlp.util.CoreMap;
import py4j.GatewayServer;
import org.ejml.simple.SimpleMatrix;

public class CoreNLPSentiScore {
static StanfordCoreNLP pipeline;

public static void init() {
Properties props = new Properties();
props.setProperty("annotators", "tokenize, ssplit, parse, sentiment");
pipeline = new StanfordCoreNLP(props);


public static void main(String[] args) {
CoreNLPSentiScore app = new CoreNLPSentiScore();
// app is now the gateway.entry_point
GatewayServer server = new GatewayServer(app);

//public static void main(String tweet) {
//public static String findSentiment(String tweet) {
public String findSentiment(String tweet) {
//String SentiReturn = "2";
//String[] SentiClass ={"very negative", "negative", "neutral", "positive", "very positive"};

//Sentiment is an integer, ranging from 0 to 4.
//0 is very negative, 1 negative, 2 neutral, 3 positive and 4 very positive.
//int sentiment = 2;
SimpleMatrix senti_score = new SimpleMatrix();
if (tweet != null && tweet.length() > 0) {
Annotation annotation = pipeline.process(tweet);

List<CoreMap> sentences = annotation.get(CoreAnnotations.SentencesAnnotation.class);
if (sentences != null && sentences.size() > 0) {

ArrayCoreMap sentence = (ArrayCoreMap) sentences.get(0);
//Tree tree = sentence.get(SentimentAnnotatedTree.class);
Tree tree = sentence.get(SentimentAnnotatedTree.class);
senti_score = RNNCoreAnnotations.getPredictions(tree);

//SentiReturn = SentiClass[sentiment];
return senti_score.toString();


Python code:

from py4j.java_gateway import JavaGateway
gateway = JavaGateway()
app = gateway.entry_point
test = 'i like this product'


Traceback (most recent call last):

File "<ipython-input-1-cefdf18ada67>", line 5, in <module>

File "C:\Anaconda3\envs\sandbox\lib\site-packages\py4j\java_gateway.py", line 1026, in __call__
answer, self.gateway_client, self.target_id, self.name)

File "C:\Anaconda3\envs\sandbox\lib\site-packages\py4j\protocol.py", line 316, in get_return_value
format(target_id, ".", name), value)

Py4JJavaError: An error occurred while calling t.findSentiment.: java.lang.NullPointerException
at CoreNLPSentiScore.findSentiment(CoreNLPSentiScore.java:43)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:237)
at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
at py4j.Gateway.invoke(Gateway.java:280)
at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
at py4j.commands.CallCommand.execute(CallCommand.java:79)
at py4j.GatewayConnection.run(GatewayConnection.java:214)
at java.lang.Thread.run(Unknown Source)


I believe you forgot to call init().

This seems to be line #43 (see your stack trace):

Annotation annotation = pipeline.process(tweet);

pipeline is likely to be null because it is instantiated in init() and init() is not called in the main() method or from Python.