/*
* listPostings displays the first n postings for a term in a
* field in an index (specified by reader). Set n to MAX_VALUE
* to display all postings.
*/
static void listPostings(IndexReader reader, String termString, String field, Integer n)
throws IOException {
System.out.println("\nPostings: " + termString + " " + field);
/*
* Prepare to access the index.
*/
BytesRef termBytes = new BytesRef(termString);
Term term = new Term(field, termBytes);
Bits liveDocs = MultiFields.getLiveDocs(reader);
/*
* Lookup the collection term frequency (ctf).
*/
long df = reader.docFreq(term);
System.out.println("\tdf: " + df);
long ctf = reader.totalTermFreq(term);
System.out.println("\tctf: " + ctf);
if (df < 1) return;
/*
* Lookup the inverted list.
*/
DocsAndPositionsEnum postings =
MultiFields.getTermPositionsEnum(reader, liveDocs, field, termBytes);
/*
* Iterate through the first n postings.
*/
long count = 0;
while ((count < n) && (postings.nextDoc() != DocIdSetIterator.NO_MORE_DOCS)) {
System.out.println("\tdocid: " + postings.docID());
int tf = postings.freq();
System.out.println("\ttf: " + tf);
System.out.print("\tPositions: ");
for (int j = 0; j < tf; j++) {
int pos = postings.nextPosition();
System.out.print(pos + " ");
}
System.out.println("");
count++;
}
;
return;
}
public static void main(String[] args) throws Exception {
// the IndexReader object is the main handle that will give you
// all the documents, terms and inverted index
IndexReader r = IndexReader.open(FSDirectory.open(new File("index")));
// You can figure out the number of documents using the maxDoc() function
System.out.println("The number of documents in this index is: " + r.maxDoc());
int i = 0;
// You can find out all the terms that have been indexed using the terms() function
TermEnum t = r.terms();
while (t.next()) {
// Since there are so many terms, let us try printing only term #100000-#100010
if (i > 100000) System.out.println("[" + i + "] " + t.term().text());
if (++i > 100010) break;
}
// You can create your own query terms by calling the Term constructor, with the field
// 'contents'
// In the following example, the query term is 'brute'
Term te = new Term("contents", "brute");
// You can also quickly find out the number of documents that have term t
System.out.println("Number of documents with the word 'brute' is: " + r.docFreq(te));
// You can use the inverted index to find out all the documents that contain the term 'brute'
// by using the termDocs function
TermDocs td = r.termDocs(te);
while (td.next()) {
System.out.println(
"Document number ["
+ td.doc()
+ "] contains the term 'brute' "
+ td.freq()
+ " time(s).");
}
// You can find the URL of the a specific document number using the document() function
// For example, the URL for document number 14191 is:
Document d = r.document(14191);
String url =
d.getFieldable("path")
.stringValue(); // the 'path' field of the Document object holds the URL
System.out.println(url.replace("%%", "/"));
// -------- Now let us use all of the functions above to make something useful --------
// The following bit of code is a worked out example of how to get a bunch of documents
// in response to a query and show them (without ranking them according to TF/IDF)
Scanner sc = new Scanner(System.in);
String str = "";
System.out.print("query> ");
while (!(str = sc.nextLine()).equals("quit")) {
String[] terms = str.split("\\s+");
for (String word : terms) {
Term term = new Term("contents", word);
TermDocs tdocs = r.termDocs(term);
while (tdocs.next()) {
String d_url =
r.document(tdocs.doc()).getFieldable("path").stringValue().replace("%%", "/");
System.out.println("[" + tdocs.doc() + "] " + d_url);
}
}
System.out.print("query> ");
}
}