Package org.apache.lucene.index

Class IndexReader

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable
    Direct Known Subclasses:
    AtomicReader, CompositeReader
    public abstract class IndexReader
extends java.lang.Object
implements java.io.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.

    There are two different types of IndexReaders:

    IndexReader instances for indexes on disk are usually constructed with a call to one of the static DirectoryReader.open() methods, e.g. DirectoryReader.open(org.apache.lucene.store.Directory). DirectoryReader implements the CompositeReader interface, it is not possible to directly get postings.

    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.

    • Method Detail

      • registerParentReader

        public final void registerParentReader​(IndexReader reader)
        Expert: This method is called by IndexReaders which wrap other readers (e.g. CompositeReader or FilterAtomicReader) 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.

      • 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 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.

        See Also:
        decRef(), incRef()

      • decRef

        public final void decRef()
                  throws java.io.IOException
        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.
        Throws:
        java.io.IOException - in case an IOException occurs in doClose()
        See Also:
        incRef()

      • equals

        public final boolean equals​(java.lang.Object obj)

        For caching purposes, IndexReader subclasses are not allowed to implement equals/hashCode, so methods are declared final. To lookup instances from caches use getCoreCacheKey() and getCombinedCoreAndDeletesKey().

        Overrides:
        equals in class java.lang.Object

      • hashCode

        public final int hashCode()

        For caching purposes, IndexReader subclasses are not allowed to implement equals/hashCode, so methods are declared final. To lookup instances from caches use getCoreCacheKey() and getCombinedCoreAndDeletesKey().

        Overrides:
        hashCode in class java.lang.Object

      • open

        @Deprecated
public static DirectoryReader open​(Directory directory)
                            throws java.io.IOException
        Deprecated.
        Use DirectoryReader.open(Directory)
        Returns a IndexReader reading the index in the given Directory
        Parameters:
        directory - the index directory
        Throws:
        java.io.IOException - if there is a low-level IO error

      • open

        @Deprecated
public static DirectoryReader open​(Directory directory,
                                   int termInfosIndexDivisor)
                            throws java.io.IOException
        Deprecated.
        Use DirectoryReader.open(Directory,int)
        Expert: Returns a IndexReader reading the index in the given Directory with the 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:
        java.io.IOException - if there is a low-level IO error

      • open

        @Deprecated
public static DirectoryReader open​(IndexWriter writer,
                                   boolean applyAllDeletes)
                            throws java.io.IOException
        Deprecated.
        Use DirectoryReader.open(IndexWriter,boolean)
        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:
        java.io.IOException - if there is a low-level IO error
        See Also:
        DirectoryReader.openIfChanged(DirectoryReader,IndexWriter,boolean)

      • open

        @Deprecated
public static DirectoryReader open​(IndexCommit commit,
                                   int termInfosIndexDivisor)
                            throws java.io.IOException
        Deprecated.
        Use DirectoryReader.open(IndexCommit,int)
        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:
        java.io.IOException - if there is a low-level IO error

      • getTermVectors

        public abstract Fields getTermVectors​(int docID)
                               throws java.io.IOException
        Retrieve term vectors for this document, or null if term vectors were not indexed. The returned Fields instance acts like a single-document inverted index (the docID will be 0).
        Throws:
        java.io.IOException

      • getTermVector

        public final Terms getTermVector​(int docID,
                                 java.lang.String field)
                          throws java.io.IOException
        Retrieve term vector for this document and field, or null if term vectors were not indexed. The returned Fields instance acts like a single-document inverted index (the docID will be 0).
        Throws:
        java.io.IOException

      • 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 abstract void document​(int docID,
                              StoredFieldVisitor visitor)
                       throws java.io.IOException
        Expert: visits the fields of a stored document, for custom processing/loading of each field. If you simply want to load all fields, use document(int). If you want to load a subset, use DocumentStoredFieldVisitor.
        Throws:
        java.io.IOException

      • document

        public final Document document​(int docID)
                        throws java.io.IOException
        Returns the stored fields of the nth Document in this index. This is just sugar for using DocumentStoredFieldVisitor.

        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 test if the doc is deleted by checking the Bits returned from MultiFields.getLiveDocs(org.apache.lucene.index.IndexReader). NOTE: only the content of a field is returned, if that field was stored during indexing. Metadata like boost, omitNorm, IndexOptions, tokenized, etc., are not preserved.

        Throws:
        java.io.IOException - if there is a low-level IO error

      • document

        public final Document document​(int docID,
                               java.util.Set<java.lang.String> fieldsToLoad)
                        throws java.io.IOException
        Like document(int) but only loads the specified fields. Note that this is simply sugar for DocumentStoredFieldVisitor(Set).
        Throws:
        java.io.IOException

      • hasDeletions

        public boolean hasDeletions()
        Returns true if any documents have been deleted. Implementers should consider overriding this method if maxDoc() or numDocs() are not constant-time operations.

      • close

        public final void close()
                 throws java.io.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 java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Throws:
        java.io.IOException - if there is a low-level IO error

      • getContext

        public abstract IndexReaderContext getContext()
        Expert: Returns the root IndexReaderContext for this IndexReader's sub-reader tree.

        Iff this reader is composed of sub readers, i.e. this reader being a composite reader, this method returns a CompositeReaderContext holding the reader's direct children as well as a view of the reader tree's atomic leaf contexts. All sub- IndexReaderContext instances referenced from this readers top-level context are private to this reader and are not shared with another context tree. For example, IndexSearcher uses this API to drive searching by one atomic leaf reader at a time. If this reader is not composed of child readers, this method returns an AtomicReaderContext.

        Note: Any of the sub-CompositeReaderContext instances referenced from this top-level context do not support CompositeReaderContext.leaves(). Only the top-level context maintains the convenience leaf-view for performance reasons.

      • leaves

        public final java.util.List<AtomicReaderContext> leaves()
        Returns the reader's leaves, or itself if this reader is atomic. This is a convenience method calling this.getContext().leaves().
        See Also:
        IndexReaderContext.leaves()

      • getCoreCacheKey

        public java.lang.Object getCoreCacheKey()
        Expert: Returns a key for this IndexReader, so FieldCache/CachingWrapperFilter can find it again. This key must not have equals()/hashCode() methods, so "equals" means "identical".

      • getCombinedCoreAndDeletesKey

        public java.lang.Object getCombinedCoreAndDeletesKey()
        Expert: Returns a key for this IndexReader that also includes deletions, so FieldCache/CachingWrapperFilter can find it again. This key must not have equals()/hashCode() methods, so "equals" means "identical".

      • docFreq

        public abstract int docFreq​(Term term)
                     throws java.io.IOException
        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.
        Throws:
        java.io.IOException
        See Also:
        TermsEnum.docFreq()

      • totalTermFreq

        public abstract long totalTermFreq​(Term term)
                            throws java.io.IOException
        Returns the total number of occurrences of term across all documents (the sum of the freq() for each doc that has this term). This will be -1 if the codec doesn't support this measure. Note that, like other term measures, this measure does not take deleted documents into account.
        Throws:
        java.io.IOException

      • getSumDocFreq

        public abstract long getSumDocFreq​(java.lang.String field)
                            throws java.io.IOException
        Returns the sum of TermsEnum.docFreq() for all terms in this field, or -1 if this measure isn't stored by the codec. Note that, just like other term measures, this measure does not take deleted documents into account.
        Throws:
        java.io.IOException
        See Also:
        Terms.getSumDocFreq()

      • getDocCount

        public abstract int getDocCount​(java.lang.String field)
                         throws java.io.IOException
        Returns the number of documents that have at least one term for this field, or -1 if this measure isn't stored by the codec. Note that, just like other term measures, this measure does not take deleted documents into account.
        Throws:
        java.io.IOException
        See Also:
        Terms.getDocCount()

      • getSumTotalTermFreq

        public abstract long getSumTotalTermFreq​(java.lang.String field)
                                  throws java.io.IOException
        Returns the sum of TermsEnum.totalTermFreq() for all terms in this field, or -1 if this measure isn't stored by the codec (or if this fields omits term freq and positions). Note that, just like other term measures, this measure does not take deleted documents into account.
        Throws:
        java.io.IOException
        See Also:
        Terms.getSumTotalTermFreq()