Lucene TF-IDF分数计算器中的NullPointerException

Question

I have made a TF-IDF score calculator in Lucene 6.1.0 . Even passing the field name and term name ,My score calculator is showing Null Pointer exception . Below is the part of code where in main class where error is there.

public static void main(String[] args) throws IOException {

Tf_Idf tfidf = new Tf_Idf();


String field = "contentfield";
        String term = "Reuters";

tfidf.scoreCalculator(field, term);    //Line 144

  }

Now scoreCalculator function is as follows:

 public void scoreCalculator (String field, String term) throws IOException 
{


    TFIDFSimilarity  tfidfSIM = new  ClassicSimilarity();

 // Bits liveDocs = MultiFields.getLiveDocs(this.indexReader);
//line 247        TermsEnum termEnum = MultiFields.getTerms(this.indexReader, field).iterator();    
    BytesRef bytesRef=null;
    while ((bytesRef = termEnum.next()) != null) {
        if(bytesRef.utf8ToString().trim().equals(term.trim())) {
            if(termEnum.seekExact(bytesRef)) {
            int doc;
                idf = tfidfSIM.idf(termEnum.docFreq(),     this.indexReader.numDocs());
                PostingsEnum docsEnum = termEnum.postings(null);
                if(docsEnum != null) {
                     doc=0;}
                    while((doc = docsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
                        tf = tfidfSIM.tf(docsEnum.freq());
                        tfidf_score = tf * idf ;
                        System.out.println(" -tfidf_score-" + tfidf_score);
                    }

            }
        }

    }

   }

}

The error Information is

     Exception in thread "main" java.lang.NullPointerException
     at Lucene.Tf_Idf.scoreCalculator(IndexFiles.java:247)
     at Lucene.IndexFiles.main(IndexFiles.java:144)

The indexing is done but score calculator is not working.Also I think I am wrong at passing values to term and field.Please help me to to figure out what to pass if not this.

EDIT:

Yes I have opened the index reader in tf- idf constructor.

class Tf_Idf {
static float tf = 1;
static float idf = 0;
private float tfidf_score;
static float [] tfidf = null;


 IndexReader indexReader;


    public Tf_Idf() throws IOException {
         String indexPath = "/home/kriti/index4";
    this.indexReader = DirectoryReader.open(FSDirectory.open(Paths.get(indexPath)));

}

Also I found that after changing //String Field="contentsfield" String Field="contents" ; Now no errors are shown but still it is not calculating the tf-idf values.Am i passing wrong string or something else is there?Besides these are some warning messages I am getting Alongside

Null point access:Variable docsEnum can only be null at this location 
The value of local variable doc is not used

These are the names of field I have given:

 static void indexDoc(IndexWriter writer, Path file, long lastModified) throws IOException {
try (InputStream stream = Files.newInputStream(file)) {
  // make a new, empty document
  Document doc = new Document();


  Field pathField = new StringField("path", file.toString(), Field.Store.YES);
  doc.add(pathField);


  Field modifiedfield=new LongPoint("modified", lastModified);
  doc.add(modifiedfield);


  Field contentfield=new TextField("contents", new BufferedReader(new InputStreamReader(stream, StandardCharsets.UTF_8)));
  doc.add(contentfield);

  if (writer.getConfig().getOpenMode() == OpenMode.CREATE) {

    System.out.println("adding " + file);
    writer.addDocument(doc);
  } else {
     System.out.println("updating " + file);
    writer.updateDocument(new Term("path", file.toString()), doc);
    }
  }
}
 }

Answer 1

Looks like this.indexReader is null. Make sure you've opened the reader (ie. in your Tf_Idf constructor) before you call the scoreCalculator method.