org.apache.lucene.index

Class IndexReader

java.lang.Object

org.apache.lucene.index.IndexReader

All Implemented Interfaces:

Closeable

Direct Known Subclasses:

AtomicReader, CompositeReader

public abstract class IndexReader
extends Object
implements 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:

• AtomicReader: These indexes do not consist of several sub-readers, they are atomic. They support retrieval of stored fields, doc values, terms, and postings.
• CompositeReader: Instances (like DirectoryReader) of this reader can only be used to get stored fields from the underlying AtomicReaders, but it is not possible to directly retrieve postings. To do that, get the sub-readers via CompositeReader.getSequentialSubReaders(). Alternatively, you can mimic an AtomicReader (with a serious slowdown), by wrapping composite readers with SlowCompositeReaderWrapper.

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	IndexReader.ReaderClosedListener A custom listener that's invoked when the IndexReader is closed.

Method Summary

Methods

Modifier and Type	Method and Description
void	addReaderClosedListener(IndexReader.ReaderClosedListener listener) Expert: adds a IndexReader.ReaderClosedListener.
void	close() Closes files associated with this index.
void	decRef() Expert: decreases the refCount of this IndexReader instance.
abstract int	docFreq(Term term) Returns the number of documents containing the term.
protected abstract void	doClose() Implements close.
Document	document(int docID) Returns the stored fields of the nth Document in this index.
Document	document(int docID, Set<String> fieldsToLoad) Like document(int) but only loads the specified fields.
abstract void	document(int docID, StoredFieldVisitor visitor) Expert: visits the fields of a stored document, for custom processing/loading of each field.
protected void	ensureOpen() Throws AlreadyClosedException if this IndexReader or any of its child readers is closed, otherwise returns.
boolean	equals(Object obj)
Object	getCombinedCoreAndDeletesKey() Expert: Returns a key for this IndexReader that also includes deletions, so FieldCache/CachingWrapperFilter can find it again.
abstract IndexReaderContext	getContext() Expert: Returns the root IndexReaderContext for this IndexReader's sub-reader tree.
Object	getCoreCacheKey() Expert: Returns a key for this IndexReader, so FieldCache/CachingWrapperFilter can find it again.
int	getRefCount() Expert: returns the current refCount for this reader
Terms	getTermVector(int docID, String field) Retrieve term vector for this document and field, or null if term vectors were not indexed.
abstract Fields	getTermVectors(int docID) Retrieve term vectors for this document, or null if term vectors were not indexed.
abstract boolean	hasDeletions() Returns true if any documents have been deleted
int	hashCode()
void	incRef() Expert: increments the refCount of this IndexReader instance.
List<AtomicReaderContext>	leaves() Returns the reader's leaves, or itself if this reader is atomic.
abstract int	maxDoc() Returns one greater than the largest possible document number.
int	numDeletedDocs() Returns the number of deleted documents.
abstract int	numDocs() Returns the number of documents in this index.
static DirectoryReader	open(Directory directory) Deprecated. Use DirectoryReader.open(Directory)
static DirectoryReader	open(Directory directory, int termInfosIndexDivisor) Deprecated. Use DirectoryReader.open(Directory,int)
static DirectoryReader	open(IndexCommit commit) Deprecated. Use DirectoryReader.open(IndexCommit)
static DirectoryReader	open(IndexCommit commit, int termInfosIndexDivisor) Deprecated. Use DirectoryReader.open(IndexCommit,int)
static DirectoryReader	open(IndexWriter writer, boolean applyAllDeletes) Deprecated. Use DirectoryReader.open(IndexWriter,boolean)
void	registerParentReader(IndexReader reader) Expert: This method is called by IndexReaders which wrap other readers (e.g.
void	removeReaderClosedListener(IndexReader.ReaderClosedListener listener) Expert: remove a previously added IndexReader.ReaderClosedListener.
abstract long	totalTermFreq(Term term) Returns the number of documents containing the term term.
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.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

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.

removeReaderClosedListener

public final void removeReaderClosedListener(IndexReader.ReaderClosedListener listener)

Expert: remove a previously added IndexReader.ReaderClosedListener.

WARNING: This API is experimental and might change in incompatible ways in the next release.

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.

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 this reader is closed. If an exception is hit, the refCount is unchanged.

Throws:

IOException - in case an IOException occurs in doClose()

See Also:

incRef()

ensureOpen

protected final void ensureOpen()
                         throws AlreadyClosedException

Throws AlreadyClosedException if this IndexReader or any of its child readers is closed, otherwise returns.

Throws:

AlreadyClosedException

equals

public final boolean equals(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 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 Object

open

@Deprecated
public static DirectoryReader open(Directory directory)
                            throws IOException

Deprecated. Use DirectoryReader.open(Directory)

Returns a IndexReader reading the index in the given Directory

Parameters:

directory - the index directory

Throws:

IOException - if there is a low-level IO error

open

@Deprecated
public static DirectoryReader open(Directory directory,
                              int termInfosIndexDivisor)
                            throws 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:

IOException - if there is a low-level IO error

open

@Deprecated
public static DirectoryReader open(IndexWriter writer,
                              boolean applyAllDeletes)
                            throws 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:

IOException - if there is a low-level IO error

See Also:

DirectoryReader.openIfChanged(DirectoryReader,IndexWriter,boolean)

WARNING: This API is experimental and might change in incompatible ways in the next release.

open

@Deprecated
public static DirectoryReader open(IndexCommit commit)
                            throws IOException

Deprecated. Use DirectoryReader.open(IndexCommit)

Expert: returns an IndexReader reading the index in the given IndexCommit.

Parameters:

commit - the commit point to open

Throws:

IOException - if there is a low-level IO error

open

@Deprecated
public static DirectoryReader open(IndexCommit commit,
                              int termInfosIndexDivisor)
                            throws 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:

IOException - if there is a low-level IO error

getTermVectors

public abstract Fields getTermVectors(int docID)
                               throws 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:

IOException

getTermVector

public final Terms getTermVector(int docID,
                  String field)
                          throws 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:

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 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:

IOException

document

public final Document document(int docID)
                        throws IOException

Returns the stored fields of the n^th 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:

IOException - if there is a low-level IO error

document

public final Document document(int docID,
                Set<String> fieldsToLoad)
                        throws IOException

Like document(int) but only loads the specified fields. Note that this is simply sugar for DocumentStoredFieldVisitor.DocumentStoredFieldVisitor(Set).

Throws:

IOException

hasDeletions

public abstract boolean hasDeletions()

Returns true if any documents have been deleted

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 Closeable

Throws:

IOException - if there is a low-level IO error

doClose

protected abstract void doClose()
                         throws IOException

Implements close.

Throws:

IOException

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 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 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 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 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:

IOException

See Also:

TermsEnum.docFreq()

totalTermFreq

public abstract long totalTermFreq(Term term)
                            throws IOException

Returns the number of documents containing the term term. This method returns 0 if the term or field does not exists, or -1 if the Codec does not support the measure. This method does not take into account deleted documents that have not yet been merged away.

Throws:

IOException

See Also:

TermsEnum.totalTermFreq()