Stanford CoreNLP给出了NullPointerException

Question

我试图了解斯坦福CoreNLP API。我希望使用以下代码将一个简单的句子标记为：

    Properties props = new Properties();
    props.put("annotators", "tokenize");
    StanfordCoreNLP pipeline = new StanfordCoreNLP(props);

    // read some text in the text variable
    String text = "I wish this code would run.";

    // create an empty Annotation just with the given text
    Annotation document = new Annotation(text);

    // run all Annotators on this text
    pipeline.annotate(document);

    // these are all the sentences in this document
    // a CoreMap is essentially a Map that uses class objects as keys and has values with custom types
    List<CoreMap> sentences = document.get(SentencesAnnotation.class);

    for(CoreMap sentence: sentences) {
        // traversing the words in the current sentence
        // a CoreLabel is a CoreMap with additional token-specific methods
        for (CoreLabel token: sentence.get(TokensAnnotation.class)) {
            // this is the text of the token
            String word = token.get(TextAnnotation.class);
            // this is the POS tag of the token
            String pos = token.get(PartOfSpeechAnnotation.class);
            // this is the NER label of the token
            String ne = token.get(NamedEntityTagAnnotation.class);       
        }

        // this is the parse tree of the current sentence
        Tree tree = sentence.get(TreeAnnotation.class);

        // this is the Stanford dependency graph of the current sentence
        SemanticGraph dependencies = sentence.get(CollapsedCCProcessedDependenciesAnnotation.class);
    }

    // This is the coreference link graph
    // Each chain stores a set of mentions that link to each other,
    // along with a method for getting the most representative mention
    // Both sentence and token offsets start at 1!
    Map<Integer, CorefChain> graph = document.get(CorefChainAnnotation.class);

这是从斯坦福NLP网站上挑选出来的，所以我希望它开箱即用。可悲的是它没有，因为它给我一个NullPointerException：

for(CoreMap sentence: sentences) {...

Answer 1

您从Stanford NLP网站上获取的代码会对文本变量执行所有注释。为了执行特定的注释，您必须相应地更改代码。

要执行标记化，这就足够了

Properties props = new Properties();
props.put("annotators", "tokenize");
StanfordCoreNLP pipeline = new StanfordCoreNLP(props);

Annotation document = new Annotation(text);
pipeline.annotate(document);
for (CoreLabel token: document.get(TokensAnnotation.class)) {
    String word = token.get(TextAnnotation.class);
}

如果注释器不包含Sentence Splitter（“ssplit”），这行代码将返回Null

document.get(SentencesAnnotation.class);

所以你遇到了NullPointerException。

Answer 2

该行检索句子注释。

List<CoreMap> sentences = document.get(SentencesAnnotation.class);

但是你的管道只包含tokenizer，而不是句子分割器。

更改以下行：

    props.put("annotators", "tokenize, ssplit"); // add sentence splitter