Lucene TF calculation

Lucene TF calc

public static final String FIELD_CONTENTS = "contents";

public HashMap<String, Long> calculateTF() {
		HashMap<String, Long> termFreqMap = new HashMap<>();
		try {
			IndexReader reader = DirectoryReader.open(FSDirectory
					.open(new File(indexFolder).toPath()));
			// String targetTerm = "breakpoint";

			Fields fields = MultiFields.getFields(reader);
			for (String field : fields) {
				Terms terms = fields.terms(field);
				TermsEnum termsEnum = terms.iterator();
				BytesRef bytesRef;
				while ((bytesRef = termsEnum.next()) != null) {
					if (termsEnum.seekExact(bytesRef)) {
						String term = bytesRef.utf8ToString();
						this.keys.add(term);
					}
				}
			}

			for (String term : this.keys) {
				Term t = new Term(FIELD_CONTENTS, term);
				// calculating the TF
				long totalTermFreq = reader.totalTermFreq(t);
				if (!termFreqMap.containsKey(term)) {
					termFreqMap.put(term, totalTermFreq);
					totalTermFreqCorpus += totalTermFreq;
				}
			}
		} catch (Exception exc) {
			// handle the exception
		}
		return termFreqMap;
	}