Instances of this reader type can only be used to get stored fields from the underlying
LeafReaders, but it is not possible to directly retrieve postings. To do that, get the LeafReaderContext for all sub-readers via #leaves().
IndexReader instances for indexes on disk are usually constructed with a call to one of the
static DirectoryReader.open() methods, e.g. DirectoryReader#open(Directory).
DirectoryReader implements the CompositeReader interface, it is not possible to
directly get postings.
Concrete subclasses of IndexReader are usually constructed with a call to one of the static
open() methods, e.g. DirectoryReader#open(Directory).
For efficiency, in this API documents are often referred to via document numbers, non-negative integers which each name a unique document in the index. These document numbers are ephemeral -- they may change as documents are added to and deleted from an index. Clients should thus not rely on a given document having the same number between sessions.
NOTE: IndexReader instances are completely thread safe, meaning multiple
threads can call any of its methods, concurrently. If your application requires external
synchronization, you should not synchronize on the IndexReader instance; use
your own (non-Lucene) objects instead.
toString()close()Closes files associated with this index. Also saves any new deletions to disk. No other methods should be called after this has been called.
| IOException | if there is a low-level IO error | |
decRef()Expert: decreases the refCount of this IndexReader instance. If the refCount drops to 0, then this reader is closed. If an exception is hit, the refCount is unchanged.
| IOException | in case an IOException occurs in doClose() | |
Returns the number of documents containing the term. This method returns 0 if the
term or field does not exists. This method does not take into account deleted documents that
have not yet been merged away.
equals(Object obj)
IndexReader subclasses are not allowed to implement equals/hashCode, so methods are
declared final.
getDocCount(String field)Returns the number of documents that have at least one term for this field. Note that, just like other term measures, this measure does not take deleted documents into account.
getSumDocFreq(String field)Returns the sum of TermsEnum#docFreq() for all terms in this field. Note that, just
like other term measures, this measure does not take deleted documents into account.
getSumTotalTermFreq(String field)Returns the sum of TermsEnum#totalTermFreq for all terms in this field. Note that, just
like other term measures, this measure does not take deleted documents into account.
hasDeletions() · also: has_deletionsReturns true if any documents have been deleted. Implementers should consider overriding this
method if #maxDoc() or #numDocs() are not constant-time operations.
hashCode()
IndexReader subclasses are not allowed to implement equals/hashCode, so methods are
declared final.
incRef()Expert: increments the refCount of this IndexReader instance. RefCounts are used to determine
when a reader can be closed safely, i.e. as soon as there are no more references. Be sure to
always call a corresponding #decRef, in a finally clause; otherwise the reader may
never be closed. Note that #close simply calls decRef(), which means that the
IndexReader will not really be closed until #decRef has been called for all outstanding
references.
Returns the reader's leaves, or itself if this reader is atomic. This is a convenience method
calling this.getContext().leaves().
maxDoc()Returns one greater than the largest possible document number. This may be used to, e.g., determine how big to allocate an array which will have an element for every document number in an index.
numDeletedDocs()Returns the number of deleted documents.
NOTE: This operation may run in O(maxDoc).
numDocs()Returns the number of documents in this index.
NOTE: This operation may run in O(maxDoc). Implementations that can't return this number in constant-time should cache it.
getReaderCacheHelper() · also: get_reader_cache_helperOptional method: Return a CacheHelper that can be used to cache based on the content of
this reader. Two readers that have different data or different sets of deleted documents will
be considered different.
A return value of null indicates that this reader is not suited for caching, which
is typically the case for short-lived wrappers that alter the content of the wrapped reader.
getRefCount() · also: get_ref_countExpert: returns the current refCount for this reader
registerParentReader(org.apache.lucene.index.IndexReader reader)Expert: This method is called by IndexReaders which wrap other readers (e.g. CompositeReader or FilterLeafReader) to register the parent at the child (this reader)
on construction of the parent. When this reader is closed, it will mark all registered parents
as closed, too. The references to parent readers are weak only, so they can be GCed once they
are no longer in use.
Returns a StoredFields reader for the stored fields of this index.
This call never returns null, even if no stored fields were indexed. The returned
instance should only be used by a single thread.
Example:
TopDocs hits = searcher.search(query, 10);
StoredFields storedFields = reader.storedFields();
for (ScoreDoc hit : hits.scoreDocs) {
Document doc = storedFields.document(hit.doc);
}
| IOException | If there is a low-level IO error | |
Returns a TermVectors reader for the term vectors of this index.
This call never returns null, even if no term vectors were indexed. The returned
instance should only be used by a single thread.
Example:
TopDocs hits = searcher.search(query, 10);
TermVectors termVectors = reader.termVectors();
for (ScoreDoc hit : hits.scoreDocs) {
Fields vector = termVectors.get(hit.doc);
}
| IOException | If there is a low-level IO error | |
Returns the total number of occurrences of term across all documents (the sum of the
freq() for each doc that has this term). Note that, like other term measures, this measure does
not take deleted documents into account.
tryIncRef()Expert: increments the refCount of this IndexReader instance only if the IndexReader has not
been closed yet and returns true iff the refCount was successfully incremented,
otherwise false. If this method returns false the reader is either
already closed or is currently being closed. Either way this reader instance shouldn't be used
by an application unless true is returned.
RefCounts are used to determine when a reader can be closed safely, i.e. as soon as there
are no more references. Be sure to always call a corresponding #decRef, in a finally
clause; otherwise the reader may never be closed. Note that #close simply calls
decRef(), which means that the IndexReader will not really be closed until #decRef has
been called for all outstanding references.