Class IndexReader

  • All Implemented Interfaces:
    Closeable, AutoCloseable, Cloneable
    Direct Known Subclasses:
    FilterIndexReader, InstantiatedIndexReader, MultiReader, ParallelReader, SegmentReader

    public abstract class IndexReader
    extends Object
    implements Cloneable, Closeable
    IndexReader is an abstract class, providing an interface for accessing an index. Search of an index is done entirely through this abstract interface, so that any subclass which implements it is searchable.

    Concrete subclasses of IndexReader are usually constructed with a call to one of the static open() methods, e.g. open(Directory, boolean).

    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.

    An IndexReader can be opened on a directory for which an IndexWriter is opened already, but it cannot be used to delete documents from the index then.

    NOTE: for backwards API compatibility, several methods are not listed as abstract, but have no useful implementations in this base class and instead always throw UnsupportedOperationException. Subclasses are strongly encouraged to override these methods, but in many cases may not need to.

    NOTE: as of 2.4, it's possible to open a read-only IndexReader using the static open methods that accept the boolean readOnly parameter. Such a reader has better concurrency as it's not necessary to synchronize on the isDeleted method. You must specify false if you want to make changes with the resulting IndexReader.

    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.

    • Field Detail

      • hasChanges

        protected boolean hasChanges
    • Constructor Detail

      • IndexReader

        protected IndexReader()
    • Method Detail

      • addReaderClosedListener

        public final void addReaderClosedListener​(IndexReader.ReaderClosedListener listener)
        Expert: adds a IndexReader.ReaderClosedListener. The provided listener will be invoked when this reader is closed.
        WARNING: This API is experimental and might change in incompatible ways in the next release.
      • getRefCount

        public final int getRefCount()
        Expert: returns the current refCount for this reader
      • incRef

        public final void 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.
        See Also:
        decRef(), tryIncRef()
      • tryIncRef

        public final boolean 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 been 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.

        See Also:
        decRef(), incRef()
      • decRef

        public final void decRef()
                          throws IOException
        Expert: decreases the refCount of this IndexReader instance. If the refCount drops to 0, then pending changes (if any) are committed to the index and this reader is closed. If an exception is hit, the refCount is unchanged.
        Throws:
        IOException - in case an IOException occurs in commit() or doClose()
        See Also:
        incRef()
      • open

        @Deprecated
        public static IndexReader open​(Directory directory,
                                       boolean readOnly)
                                throws CorruptIndexException,
                                       IOException
        Deprecated.
        Write support will be removed in Lucene 4.0. Use open(Directory) instead
        Returns an IndexReader reading the index in the given Directory. You should pass readOnly=true, since it gives much better concurrent performance, unless you intend to do write operations (delete documents or change norms) with the reader.
        Parameters:
        directory - the index directory
        readOnly - true if no changes (deletions, norms) will be made with this IndexReader
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • open

        public static IndexReader open​(IndexWriter writer,
                                       boolean applyAllDeletes)
                                throws CorruptIndexException,
                                       IOException
        Open a near real time IndexReader from the IndexWriter.
        Parameters:
        writer - The IndexWriter to open from
        applyAllDeletes - If true, all buffered deletes will be applied (made visible) in the returned reader. If false, the deletes are not applied but remain buffered (in IndexWriter) so that they will be applied in the future. Applying deletes can be costly, so if your app can tolerate deleted documents being returned you might gain some performance by passing false.
        Returns:
        The new IndexReader
        Throws:
        CorruptIndexException
        IOException - if there is a low-level IO error
        See Also:
        openIfChanged(IndexReader,IndexWriter,boolean)
        WARNING: This API is experimental and might change in incompatible ways in the next release.
      • open

        @Deprecated
        public static IndexReader open​(IndexCommit commit,
                                       boolean readOnly)
                                throws CorruptIndexException,
                                       IOException
        Deprecated.
        Write support will be removed in Lucene 4.0. Use open(IndexCommit) instead
        Expert: returns an IndexReader reading the index in the given IndexCommit. You should pass readOnly=true, since it gives much better concurrent performance, unless you intend to do write operations (delete documents or change norms) with the reader.
        Parameters:
        commit - the commit point to open
        readOnly - true if no changes (deletions, norms) will be made with this IndexReader
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • open

        @Deprecated
        public static IndexReader open​(Directory directory,
                                       IndexDeletionPolicy deletionPolicy,
                                       boolean readOnly)
                                throws CorruptIndexException,
                                       IOException
        Deprecated.
        Write support will be removed in Lucene 4.0. Use open(Directory) instead
        Expert: returns an IndexReader reading the index in the given Directory, with a custom IndexDeletionPolicy. You should pass readOnly=true, since it gives much better concurrent performance, unless you intend to do write operations (delete documents or change norms) with the reader.
        Parameters:
        directory - the index directory
        deletionPolicy - a custom deletion policy (only used if you use this reader to perform deletes or to set norms); see IndexWriter for details.
        readOnly - true if no changes (deletions, norms) will be made with this IndexReader
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • open

        @Deprecated
        public static IndexReader open​(Directory directory,
                                       IndexDeletionPolicy deletionPolicy,
                                       boolean readOnly,
                                       int termInfosIndexDivisor)
                                throws CorruptIndexException,
                                       IOException
        Deprecated.
        Write support will be removed in Lucene 4.0. Use open(Directory,int) instead
        Expert: returns an IndexReader reading the index in the given Directory, with a custom IndexDeletionPolicy. You should pass readOnly=true, since it gives much better concurrent performance, unless you intend to do write operations (delete documents or change norms) with the reader.
        Parameters:
        directory - the index directory
        deletionPolicy - a custom deletion policy (only used if you use this reader to perform deletes or to set norms); see IndexWriter for details.
        readOnly - true if no changes (deletions, norms) will be made with this IndexReader
        termInfosIndexDivisor - Subsamples which indexed terms are loaded into RAM. This has the same effect as IndexWriter.setTermIndexInterval(int) except that setting must be done at indexing time while this setting can be set per reader. When set to N, then one in every N*termIndexInterval terms in the index is loaded into memory. By setting this to a value > 1 you can reduce memory usage, at the expense of higher latency when loading a TermInfo. The default value is 1. Set this to -1 to skip loading the terms index entirely.
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • open

        @Deprecated
        public static IndexReader open​(IndexCommit commit,
                                       IndexDeletionPolicy deletionPolicy,
                                       boolean readOnly,
                                       int termInfosIndexDivisor)
                                throws CorruptIndexException,
                                       IOException
        Deprecated.
        Write support will be removed in Lucene 4.0. Use open(IndexCommit,int) instead
        Expert: returns an IndexReader reading the index in the given Directory, using a specific commit and with a custom IndexDeletionPolicy. You should pass readOnly=true, since it gives much better concurrent performance, unless you intend to do write operations (delete documents or change norms) with the reader.
        Parameters:
        commit - the specific IndexCommit to open; see listCommits(org.apache.lucene.store.Directory) to list all commits in a directory
        deletionPolicy - a custom deletion policy (only used if you use this reader to perform deletes or to set norms); see IndexWriter for details.
        readOnly - true if no changes (deletions, norms) will be made with this IndexReader
        termInfosIndexDivisor - Subsamples which indexed terms are loaded into RAM. This has the same effect as IndexWriter.setTermIndexInterval(int) except that setting must be done at indexing time while this setting can be set per reader. When set to N, then one in every N*termIndexInterval terms in the index is loaded into memory. By setting this to a value > 1 you can reduce memory usage, at the expense of higher latency when loading a TermInfo. The default value is 1. Set this to -1 to skip loading the terms index entirely. This is only useful in advanced situations when you will only .next() through all terms; attempts to seek will hit an exception.
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • open

        public static IndexReader open​(Directory directory,
                                       int termInfosIndexDivisor)
                                throws CorruptIndexException,
                                       IOException
        Expert: Returns a IndexReader reading the index in the given Director and given termInfosIndexDivisor
        Parameters:
        directory - the index directory
        termInfosIndexDivisor - Subsamples which indexed terms are loaded into RAM. This has the same effect as IndexWriterConfig.setTermIndexInterval(int) except that setting must be done at indexing time while this setting can be set per reader. When set to N, then one in every N*termIndexInterval terms in the index is loaded into memory. By setting this to a value > 1 you can reduce memory usage, at the expense of higher latency when loading a TermInfo. The default value is 1. Set this to -1 to skip loading the terms index entirely.
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • open

        public static IndexReader open​(IndexCommit commit,
                                       int termInfosIndexDivisor)
                                throws CorruptIndexException,
                                       IOException
        Expert: returns an IndexReader reading the index in the given IndexCommit and termInfosIndexDivisor.
        Parameters:
        commit - the commit point to open
        termInfosIndexDivisor - Subsamples which indexed terms are loaded into RAM. This has the same effect as IndexWriterConfig.setTermIndexInterval(int) except that setting must be done at indexing time while this setting can be set per reader. When set to N, then one in every N*termIndexInterval terms in the index is loaded into memory. By setting this to a value > 1 you can reduce memory usage, at the expense of higher latency when loading a TermInfo. The default value is 1. Set this to -1 to skip loading the terms index entirely.
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • openIfChanged

        public static IndexReader openIfChanged​(IndexReader oldReader)
                                         throws IOException
        If the index has changed since the provided reader was opened, open and return a new reader; else, return null. The new reader, if not null, will be the same type of reader as the previous one, ie an NRT reader will open a new NRT reader, a MultiReader will open a new MultiReader, etc.

        This method is typically far less costly than opening a fully new IndexReader as it shares resources (for example sub-readers) with the provided IndexReader, when possible.

        The provided reader is not closed (you are responsible for doing so); if a new reader is returned you also must eventually close it. Be sure to never close a reader while other threads are still using it; see SearcherManager to simplify managing this.

        If a new reader is returned, it's safe to make changes (deletions, norms) with it. All shared mutable state with the old reader uses "copy on write" semantics to ensure the changes are not seen by other readers.

        Returns:
        null if there are no changes; else, a new IndexReader instance which you must eventually close
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • openIfChanged

        public static IndexReader openIfChanged​(IndexReader oldReader,
                                                IndexWriter writer,
                                                boolean applyAllDeletes)
                                         throws IOException
        Expert: If there changes (committed or not) in the IndexWriter versus what the provided reader is searching, then open and return a new read-only IndexReader searching both committed and uncommitted changes from the writer; else, return null (though, the current implementation never returns null).

        This provides "near real-time" searching, in that changes made during an IndexWriter session can be quickly made available for searching without closing the writer nor calling IndexWriter.commit().

        It's near real-time because there is no hard guarantee on how quickly you can get a new reader after making changes with IndexWriter. You'll have to experiment in your situation to determine if it's fast enough. As this is a new and experimental feature, please report back on your findings so we can learn, improve and iterate.

        The very first time this method is called, this writer instance will make every effort to pool the readers that it opens for doing merges, applying deletes, etc. This means additional resources (RAM, file descriptors, CPU time) will be consumed.

        For lower latency on reopening a reader, you should call IndexWriterConfig.setMergedSegmentWarmer(org.apache.lucene.index.IndexWriter.IndexReaderWarmer) to pre-warm a newly merged segment before it's committed to the index. This is important for minimizing index-to-search delay after a large merge.

        If an addIndexes* call is running in another thread, then this reader will only search those segments from the foreign index that have been successfully copied over, so far.

        NOTE: Once the writer is closed, any outstanding readers may continue to be used. However, if you attempt to reopen any of those readers, you'll hit an AlreadyClosedException.

        Parameters:
        writer - The IndexWriter to open from
        applyAllDeletes - If true, all buffered deletes will be applied (made visible) in the returned reader. If false, the deletes are not applied but remain buffered (in IndexWriter) so that they will be applied in the future. Applying deletes can be costly, so if your app can tolerate deleted documents being returned you might gain some performance by passing false.
        Returns:
        IndexReader that covers entire index plus all changes made so far by this IndexWriter instance, or null if there are no new changes
        Throws:
        IOException
        WARNING: This API is experimental and might change in incompatible ways in the next release.
      • reopen

        @Deprecated
        public IndexReader reopen()
                           throws CorruptIndexException,
                                  IOException
        Deprecated.
        Refreshes an IndexReader if the index has changed since this instance was (re)opened.

        Opening an IndexReader is an expensive operation. This method can be used to refresh an existing IndexReader to reduce these costs. This method tries to only load segments that have changed or were created after the IndexReader was (re)opened.

        If the index has not changed since this instance was (re)opened, then this call is a NOOP and returns this instance. Otherwise, a new instance is returned. The old instance is not closed and remains usable.

        If the reader is reopened, even though they share resources internally, it's safe to make changes (deletions, norms) with the new reader. All shared mutable state obeys "copy on write" semantics to ensure the changes are not seen by other readers.

        You can determine whether a reader was actually reopened by comparing the old instance with the instance returned by this method:

         IndexReader reader = ... 
         ...
         IndexReader newReader = r.reopen();
         if (newReader != reader) {
         ...     // reader was reopened
           reader.close(); 
         }
         reader = newReader;
         ...
         
        Be sure to synchronize that code so that other threads, if present, can never use reader after it has been closed and before it's switched to newReader.

        NOTE: If this reader is a near real-time reader (obtained from IndexWriter.getReader(), reopen() will simply call writer.getReader() again for you, though this may change in the future.

        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • reopen

        @Deprecated
        public IndexReader reopen​(IndexWriter writer,
                                  boolean applyAllDeletes)
                           throws CorruptIndexException,
                                  IOException
        Expert: returns a readonly reader, covering all committed as well as un-committed changes to the index. This provides "near real-time" searching, in that changes made during an IndexWriter session can be quickly made available for searching without closing the writer nor calling commit().

        Note that this is functionally equivalent to calling {#flush} (an internal IndexWriter operation) and then using open(org.apache.lucene.store.Directory) to open a new reader. But the turnaround time of this method should be faster since it avoids the potentially costly commit().

        You must close the IndexReader returned by this method once you are done using it.

        It's near real-time because there is no hard guarantee on how quickly you can get a new reader after making changes with IndexWriter. You'll have to experiment in your situation to determine if it's fast enough. As this is a new and experimental feature, please report back on your findings so we can learn, improve and iterate.

        The resulting reader supports reopen(), but that call will simply forward back to this method (though this may change in the future).

        The very first time this method is called, this writer instance will make every effort to pool the readers that it opens for doing merges, applying deletes, etc. This means additional resources (RAM, file descriptors, CPU time) will be consumed.

        For lower latency on reopening a reader, you should call IndexWriterConfig.setMergedSegmentWarmer(org.apache.lucene.index.IndexWriter.IndexReaderWarmer) to pre-warm a newly merged segment before it's committed to the index. This is important for minimizing index-to-search delay after a large merge.

        If an addIndexes* call is running in another thread, then this reader will only search those segments from the foreign index that have been successfully copied over, so far

        .

        NOTE: Once the writer is closed, any outstanding readers may continue to be used. However, if you attempt to reopen any of those readers, you'll hit an AlreadyClosedException.

        Parameters:
        writer - The IndexWriter to open from
        applyAllDeletes - If true, all buffered deletes will be applied (made visible) in the returned reader. If false, the deletes are not applied but remain buffered (in IndexWriter) so that they will be applied in the future. Applying deletes can be costly, so if your app can tolerate deleted documents being returned you might gain some performance by passing false.
        Returns:
        IndexReader that covers entire index plus all changes made so far by this IndexWriter instance
        Throws:
        IOException
        CorruptIndexException
        WARNING: This API is experimental and might change in incompatible ways in the next release.
      • clone

        public Object clone()
        Efficiently clones the IndexReader (sharing most internal state).

        On cloning a reader with pending changes (deletions, norms), the original reader transfers its write lock to the cloned reader. This means only the cloned reader may make further changes to the index, and commit the changes to the index on close, but the old reader still reflects all changes made up until it was cloned.

        Like openIfChanged(IndexReader), it's safe to make changes to either the original or the cloned reader: all shared mutable state obeys "copy on write" semantics to ensure the changes are not seen by other readers.

        Overrides:
        clone in class Object
      • directory

        public Directory directory()
        Returns the directory associated with this index. The Default implementation returns the directory specified by subclasses when delegating to the IndexReader(Directory) constructor, or throws an UnsupportedOperationException if one was not specified.
        Throws:
        UnsupportedOperationException - if no directory
      • getCurrentVersion

        @Deprecated
        public static long getCurrentVersion​(Directory directory)
                                      throws CorruptIndexException,
                                             IOException
        Deprecated.
        Use getVersion() on an opened IndexReader.
        Reads version number from segments files. The version number is initialized with a timestamp and then increased by one for each change of the index.
        Parameters:
        directory - where the index resides.
        Returns:
        version number.
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • getTermFreqVectors

        public abstract TermFreqVector[] getTermFreqVectors​(int docNumber)
                                                     throws IOException
        Return an array of term frequency vectors for the specified document. The array contains a vector for each vectorized field in the document. Each vector contains terms and frequencies for all terms in a given vectorized field. If no such fields existed, the method returns null. The term vectors that are returned may either be of type TermFreqVector or of type TermPositionVector if positions or offsets have been stored.
        Parameters:
        docNumber - document for which term frequency vectors are returned
        Returns:
        array of term frequency vectors. May be null if no term vectors have been stored for the specified document.
        Throws:
        IOException - if index cannot be accessed
        See Also:
        Field.TermVector
      • getTermFreqVector

        public abstract TermFreqVector getTermFreqVector​(int docNumber,
                                                         String field)
                                                  throws IOException
        Return a term frequency vector for the specified document and field. The returned vector contains terms and frequencies for the terms in the specified field of this document, if the field had the storeTermVector flag set. If termvectors had been stored with positions or offsets, a TermPositionVector is returned.
        Parameters:
        docNumber - document for which the term frequency vector is returned
        field - field for which the term frequency vector is returned.
        Returns:
        term frequency vector May be null if field does not exist in the specified document or term vector was not stored.
        Throws:
        IOException - if index cannot be accessed
        See Also:
        Field.TermVector
      • getTermFreqVector

        public abstract void getTermFreqVector​(int docNumber,
                                               String field,
                                               TermVectorMapper mapper)
                                        throws IOException
        Load the Term Vector into a user-defined data structure instead of relying on the parallel arrays of the TermFreqVector.
        Parameters:
        docNumber - The number of the document to load the vector for
        field - The name of the field to load
        mapper - The TermVectorMapper to process the vector. Must not be null
        Throws:
        IOException - if term vectors cannot be accessed or if they do not exist on the field and doc. specified.
      • getTermFreqVector

        public abstract void getTermFreqVector​(int docNumber,
                                               TermVectorMapper mapper)
                                        throws IOException
        Map all the term vectors for all fields in a Document
        Parameters:
        docNumber - The number of the document to load the vector for
        mapper - The TermVectorMapper to process the vector. Must not be null
        Throws:
        IOException - if term vectors cannot be accessed or if they do not exist on the field and doc. specified.
      • indexExists

        public static boolean indexExists​(Directory directory)
                                   throws IOException
        Returns true if an index exists at the specified directory.
        Parameters:
        directory - the directory to check for an index
        Returns:
        true if an index exists; false otherwise
        Throws:
        IOException - if there is a problem with accessing the index
      • numDocs

        public abstract int numDocs()
        Returns the number of documents in this index.
      • maxDoc

        public abstract int 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

        public final int numDeletedDocs()
        Returns the number of deleted documents.
      • document

        public final Document document​(int n)
                                throws CorruptIndexException,
                                       IOException
        Returns the stored fields of the nth Document in this index.

        NOTE: for performance reasons, this method does not check if the requested document is deleted, and therefore asking for a deleted document may yield unspecified results. Usually this is not required, however you can call isDeleted(int) with the requested document ID to verify the document is not deleted.

        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • document

        public abstract Document document​(int n,
                                          FieldSelector fieldSelector)
                                   throws CorruptIndexException,
                                          IOException
        Get the Document at the n th position. The FieldSelector may be used to determine what Fields to load and how they should be loaded. NOTE: If this Reader (more specifically, the underlying FieldsReader) is closed before the lazy Field is loaded an exception may be thrown. If you want the value of a lazy Field to be available after closing you must explicitly load it or fetch the Document again with a new loader.

        NOTE: for performance reasons, this method does not check if the requested document is deleted, and therefore asking for a deleted document may yield unspecified results. Usually this is not required, however you can call isDeleted(int) with the requested document ID to verify the document is not deleted.

        Parameters:
        n - Get the document at the nth position
        fieldSelector - The FieldSelector to use to determine what Fields should be loaded on the Document. May be null, in which case all Fields will be loaded.
        Returns:
        The stored fields of the Document at the nth position
        Throws:
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
        See Also:
        Fieldable, FieldSelector, SetBasedFieldSelector, LoadFirstFieldSelector
      • isDeleted

        public abstract boolean isDeleted​(int n)
        Returns true if document n has been deleted
      • hasDeletions

        public abstract boolean hasDeletions()
        Returns true if any documents have been deleted
      • hasNorms

        public boolean hasNorms​(String field)
                         throws IOException
        Returns true if there are norms stored for this field.
        Throws:
        IOException
      • norms

        public abstract byte[] norms​(String field)
                              throws IOException
        Returns the byte-encoded normalization factor for the named field of every document. This is used by the search code to score documents. Returns null if norms were not indexed for this field.
        Throws:
        IOException
        See Also:
        AbstractField.setBoost(float)
      • norms

        public abstract void norms​(String field,
                                   byte[] bytes,
                                   int offset)
                            throws IOException
        Reads the byte-encoded normalization factor for the named field of every document. This is used by the search code to score documents.
        Throws:
        IOException
        See Also:
        AbstractField.setBoost(float)
      • terms

        public abstract TermEnum terms()
                                throws IOException
        Returns an enumeration of all the terms in the index. The enumeration is ordered by Term.compareTo(). Each term is greater than all that precede it in the enumeration. Note that after calling terms(), TermEnum.next() must be called on the resulting enumeration before calling other methods such as TermEnum.term().
        Throws:
        IOException - if there is a low-level IO error
      • terms

        public abstract TermEnum terms​(Term t)
                                throws IOException
        Returns an enumeration of all terms starting at a given term. If the given term does not exist, the enumeration is positioned at the first term greater than the supplied term. The enumeration is ordered by Term.compareTo(). Each term is greater than all that precede it in the enumeration.
        Throws:
        IOException - if there is a low-level IO error
      • docFreq

        public abstract int docFreq​(Term t)
                             throws IOException
        Returns the number of documents containing the term t.
        Throws:
        IOException - if there is a low-level IO error
      • termDocs

        public TermDocs termDocs​(Term term)
                          throws IOException
        Returns an enumeration of all the documents which contain term. For each document, the document number, the frequency of the term in that document is also provided, for use in search scoring. If term is null, then all non-deleted docs are returned with freq=1. Thus, this method implements the mapping:

          Term    =>    <docNum, freq>*

        The enumeration is ordered by document number. Each document number is greater than all that precede it in the enumeration.

        Throws:
        IOException - if there is a low-level IO error
      • termPositions

        public final TermPositions termPositions​(Term term)
                                          throws IOException
        Returns an enumeration of all the documents which contain term. For each document, in addition to the document number and frequency of the term in that document, a list of all of the ordinal positions of the term in the document is available. Thus, this method implements the mapping:

          Term    =>    <docNum, freq, <pos1, pos2, ... posfreq-1> >*

        This positional information facilitates phrase and proximity searching.

        The enumeration is ordered by document number. Each document number is greater than all that precede it in the enumeration.

        Throws:
        IOException - if there is a low-level IO error
      • undeleteAll

        @Deprecated
        public final void undeleteAll()
                               throws StaleReaderException,
                                      CorruptIndexException,
                                      LockObtainFailedException,
                                      IOException
        Deprecated.
        Write support will be removed in Lucene 4.0. There will be no replacement for this method.
        Undeletes all documents currently marked as deleted in this index.

        NOTE: this method can only recover documents marked for deletion but not yet removed from the index; when and how Lucene removes deleted documents is an implementation detail, subject to change from release to release. However, you can use numDeletedDocs() on the current IndexReader instance to see how many documents will be un-deleted.

        Throws:
        StaleReaderException - if the index has changed since this reader was opened
        LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)
        CorruptIndexException - if the index is corrupt
        IOException - if there is a low-level IO error
      • acquireWriteLock

        @Deprecated
        protected void acquireWriteLock()
                                 throws IOException
        Deprecated.
        Write support will be removed in Lucene 4.0.
        Does nothing by default. Subclasses that require a write lock for index modifications must implement this method.
        Throws:
        IOException
      • commit

        @Deprecated
        protected final void commit()
                             throws IOException
        Deprecated.
        Write support will be removed in Lucene 4.0.
        Commit changes resulting from delete, undeleteAll, or setNorm operations If an exception is hit, then either no changes or all changes will have been committed to the index (transactional semantics).
        Throws:
        IOException - if there is a low-level IO error
      • commit

        @Deprecated
        public final void commit​(Map<String,​String> commitUserData)
                          throws IOException
        Deprecated.
        Write support will be removed in Lucene 4.0.
        Commit changes resulting from delete, undeleteAll, or setNorm operations If an exception is hit, then either no changes or all changes will have been committed to the index (transactional semantics).
        Throws:
        IOException - if there is a low-level IO error
      • close

        public final void close()
                         throws IOException
        Closes files associated with this index. Also saves any new deletions to disk. No other methods should be called after this has been called.
        Specified by:
        close in interface AutoCloseable
        Specified by:
        close in interface Closeable
        Throws:
        IOException - if there is a low-level IO error
      • getFieldInfos

        public abstract FieldInfos getFieldInfos()
        Get the FieldInfos describing all fields in this reader. NOTE: do not make any changes to the returned FieldInfos!
        WARNING: This API is experimental and might change in incompatible ways in the next release.
      • getIndexCommit

        public IndexCommit getIndexCommit()
                                   throws IOException
        Expert: return the IndexCommit that this reader has opened. This method is only implemented by those readers that correspond to a Directory with its own segments_N file.
        Throws:
        IOException
        WARNING: This API is experimental and might change in incompatible ways in the next release.
      • getSequentialSubReaders

        public IndexReader[] getSequentialSubReaders()
        Expert: returns the sequential sub readers that this reader is logically composed of. For example, IndexSearcher uses this API to drive searching by one sub reader at a time. If this reader is not composed of sequential child readers, it should return null. If this method returns an empty array, that means this reader is a null reader (for example a MultiReader that has no sub readers).

        NOTE: You should not try using sub-readers returned by this method to make any changes (setNorm, deleteDocument, etc.). While this might succeed for one composite reader (like MultiReader), it will most likely lead to index corruption for other readers (like DirectoryReader obtained through open(org.apache.lucene.store.Directory). Use the parent reader directly.

      • getCoreCacheKey

        public Object getCoreCacheKey()
        Expert
      • getDeletesCacheKey

        public Object getDeletesCacheKey()
        Expert. Warning: this returns null if the reader has no deletions
      • getUniqueTermCount

        public long getUniqueTermCount()
                                throws IOException
        Returns the number of unique terms (across all fields) in this reader. This method returns long, even though internally Lucene cannot handle more than 2^31 unique terms, for a possible future when this limitation is removed.
        Throws:
        UnsupportedOperationException - if this count cannot be easily determined (eg Multi*Readers). Instead, you should call getSequentialSubReaders() and ask each sub reader for its unique term count.
        IOException
      • getTermInfosIndexDivisor

        public int getTermInfosIndexDivisor()
        For IndexReader implementations that use TermInfosReader to read terms, this returns the current indexDivisor as specified when the reader was opened.