org.apache.lucene.index
Class IndexReader

java.lang.Object
  org.apache.lucene.index.IndexReader

All Implemented Interfaces:

Closeable, 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.

Nested Class Summary

static class

IndexReader.FieldOption Constants describing field properties, for example used for getFieldNames(FieldOption).

Field Summary

protected boolean

hasChanges

Constructor Summary

protected

IndexReader()

Method Summary

protected void	acquireWriteLock() Does nothing by default.
Object	clone() Efficiently clones the IndexReader (sharing most internal state).
IndexReader	clone(boolean openReadOnly) Clones the IndexReader and optionally changes readOnly.
void	close() Closes files associated with this index.
protected void	commit() 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).
void	commit(Map<String,String> commitUserData) 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).
void	decRef() Expert: decreases the refCount of this IndexReader instance.
void	deleteDocument(int docNum) Deletes the document numbered docNum.
int	deleteDocuments(Term term) Deletes all documents that have a given term indexed.
Directory	directory() Returns the directory associated with this index.
abstract int	docFreq(Term t) Returns the number of documents containing the term t.
protected abstract void	doClose() Implements close.
protected abstract void	doCommit(Map<String,String> commitUserData) Implements commit.
Document	document(int n) Returns the stored fields of the nth Document in this index.
abstract Document	document(int n, FieldSelector fieldSelector) Get the Document at the n th position.
protected abstract void	doDelete(int docNum) Implements deletion of the document numbered docNum.
protected abstract void	doSetNorm(int doc, String field, byte value) Implements setNorm in subclass.
protected abstract void	doUndeleteAll() Implements actual undeleteAll() in subclass.
protected void	ensureOpen()
void	flush()
void	flush(Map<String,String> commitUserData)
Map<String,String>	getCommitUserData() Retrieve the String userData optionally passed to IndexWriter#commit.
static Map<String,String>	getCommitUserData(Directory directory) Reads commitUserData, previously passed to IndexWriter.commit(Map), from current index segments file.
static long	getCurrentVersion(Directory directory) Reads version number from segments files.
Object	getDeletesCacheKey() Expert.
Object	getFieldCacheKey() Expert
abstract Collection<String>	getFieldNames(IndexReader.FieldOption fldOption) Get a list of unique field names that exist in this index and have the specified field option information.
IndexCommit	getIndexCommit() Expert: return the IndexCommit that this reader has opened.
int	getRefCount() Expert: returns the current refCount for this reader
IndexReader[]	getSequentialSubReaders() Expert: returns the sequential sub readers that this reader is logically composed of.
abstract TermFreqVector	getTermFreqVector(int docNumber, String field) Return a term frequency vector for the specified document and field.
abstract void	getTermFreqVector(int docNumber, String field, TermVectorMapper mapper) Load the Term Vector into a user-defined data structure instead of relying on the parallel arrays of the TermFreqVector.
abstract void	getTermFreqVector(int docNumber, TermVectorMapper mapper) Map all the term vectors for all fields in a Document
abstract TermFreqVector[]	getTermFreqVectors(int docNumber) Return an array of term frequency vectors for the specified document.
int	getTermInfosIndexDivisor() For IndexReader implementations that use TermInfosReader to read terms, this returns the current indexDivisor as specified when the reader was opened.
long	getUniqueTermCount() Returns the number of unique terms (across all fields) in this reader.
long	getVersion() Version number when this IndexReader was opened.
abstract boolean	hasDeletions() Returns true if any documents have been deleted
boolean	hasNorms(String field) Returns true if there are norms stored for this field.
void	incRef() Expert: increments the refCount of this IndexReader instance.
static boolean	indexExists(Directory directory) Returns true if an index exists at the specified directory.
boolean	isCurrent() Check whether any new changes have occurred to the index since this reader was opened.
abstract boolean	isDeleted(int n) Returns true if document n has been deleted
boolean	isOptimized() Checks is the index is optimized (if it has a single segment and no deletions).
static long	lastModified(Directory directory2) Returns the time the index in the named directory was last modified.
static Collection<IndexCommit>	listCommits(Directory dir) Returns all commit points that exist in the Directory.
static void	main(String[] args) Prints the filename and size of each file within a given compound file.
abstract int	maxDoc() Returns one greater than the largest possible document number.
abstract byte[]	norms(String field) Returns the byte-encoded normalization factor for the named field of every document.
abstract void	norms(String field, byte[] bytes, int offset) Reads the byte-encoded normalization factor for the named field of every document.
int	numDeletedDocs() Returns the number of deleted documents.
abstract int	numDocs() Returns the number of documents in this index.
static IndexReader	open(Directory directory) Returns a IndexReader reading the index in the given Directory, with readOnly=true.
static IndexReader	open(Directory directory, boolean readOnly) Returns an IndexReader reading the index in the given Directory.
static IndexReader	open(Directory directory, IndexDeletionPolicy deletionPolicy, boolean readOnly) Expert: returns an IndexReader reading the index in the given Directory, with a custom IndexDeletionPolicy.
static IndexReader	open(Directory directory, IndexDeletionPolicy deletionPolicy, boolean readOnly, int termInfosIndexDivisor) Expert: returns an IndexReader reading the index in the given Directory, with a custom IndexDeletionPolicy.
static IndexReader	open(IndexCommit commit, boolean readOnly) Expert: returns an IndexReader reading the index in the given IndexCommit.
static IndexReader	open(IndexCommit commit, IndexDeletionPolicy deletionPolicy, boolean readOnly) Expert: returns an IndexReader reading the index in the given Directory, using a specific commit and with a custom IndexDeletionPolicy.
static IndexReader	open(IndexCommit commit, IndexDeletionPolicy deletionPolicy, boolean readOnly, int termInfosIndexDivisor) Expert: returns an IndexReader reading the index in the given Directory, using a specific commit and with a custom IndexDeletionPolicy.
IndexReader	reopen() Refreshes an IndexReader if the index has changed since this instance was (re)opened.
IndexReader	reopen(boolean openReadOnly) Just like reopen(), except you can change the readOnly of the original reader.
IndexReader	reopen(IndexCommit commit) Expert: reopen this reader on a specific commit point.
void	setNorm(int doc, String field, byte value) Expert: Resets the normalization factor for the named field of the named document.
void	setNorm(int doc, String field, float value) Expert: Resets the normalization factor for the named field of the named document.
abstract TermDocs	termDocs() Returns an unpositioned TermDocs enumerator.
TermDocs	termDocs(Term term) Returns an enumeration of all the documents which contain term.
abstract TermPositions	termPositions() Returns an unpositioned TermPositions enumerator.
TermPositions	termPositions(Term term) Returns an enumeration of all the documents which contain term.
abstract TermEnum	terms() Returns an enumeration of all the terms in the index.
abstract TermEnum	terms(Term t) Returns an enumeration of all terms starting at a given term.
void	undeleteAll() Undeletes all documents currently marked as deleted in this index.

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

hasChanges

protected boolean hasChanges

Constructor Detail

IndexReader

protected IndexReader()

Method Detail

getRefCount

public int getRefCount()

Expert: returns the current refCount for this reader

incRef

public 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()

decRef

public 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.

Throws:

IOException - in case an IOException occurs in commit() or doClose()

See Also:

incRef()

ensureOpen

protected final void ensureOpen()
                         throws AlreadyClosedException

Throws:

AlreadyClosedException - if this IndexReader is closed

open

public static IndexReader open(Directory directory)
                        throws CorruptIndexException,
                               IOException

Returns a IndexReader reading the index in the given Directory, with readOnly=true.

Parameters:

directory - the index directory

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

open

public static IndexReader open(Directory directory,
                               boolean readOnly)
                        throws CorruptIndexException,
                               IOException

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(IndexCommit commit,
                               boolean readOnly)
                        throws CorruptIndexException,
                               IOException

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

public static IndexReader open(Directory directory,
                               IndexDeletionPolicy deletionPolicy,
                               boolean readOnly)
                        throws CorruptIndexException,
                               IOException

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

public static IndexReader open(Directory directory,
                               IndexDeletionPolicy deletionPolicy,
                               boolean readOnly,
                               int termInfosIndexDivisor)
                        throws CorruptIndexException,
                               IOException

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

public static IndexReader open(IndexCommit commit,
                               IndexDeletionPolicy deletionPolicy,
                               boolean readOnly)
                        throws CorruptIndexException,
                               IOException

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

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

open

public static IndexReader open(IndexCommit commit,
                               IndexDeletionPolicy deletionPolicy,
                               boolean readOnly,
                               int termInfosIndexDivisor)
                        throws CorruptIndexException,
                               IOException

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.

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

reopen

public IndexReader reopen()
                   throws CorruptIndexException,
                          IOException

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

public IndexReader reopen(boolean openReadOnly)
                   throws CorruptIndexException,
                          IOException

Just like reopen(), except you can change the readOnly of the original reader. If the index is unchanged but readOnly is different then a new reader will be returned.

Throws:

CorruptIndexException

IOException

reopen

public IndexReader reopen(IndexCommit commit)
                   throws CorruptIndexException,
                          IOException

Expert: reopen this reader on a specific commit point. This always returns a readOnly reader. If the specified commit point matches what this reader is already on, and this reader is already readOnly, then this same instance is returned; if it is not already readOnly, a readOnly clone is returned.

Throws:

CorruptIndexException

IOException

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 reopen(), 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

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

clone

public IndexReader clone(boolean openReadOnly)
                  throws CorruptIndexException,
                         IOException

Clones the IndexReader and optionally changes readOnly. A readOnly reader cannot open a writeable reader.

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

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

lastModified

public static long lastModified(Directory directory2)
                         throws CorruptIndexException,
                                IOException

Returns the time the index in the named directory was last modified. Do not use this to check whether the reader is still up-to-date, use isCurrent() instead.

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

getCurrentVersion

public static long getCurrentVersion(Directory directory)
                              throws CorruptIndexException,
                                     IOException

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

getCommitUserData

public static Map<String,String> getCommitUserData(Directory directory)
                                            throws CorruptIndexException,
                                                   IOException

Reads commitUserData, previously passed to IndexWriter.commit(Map), from current index segments file. This will return null if IndexWriter.commit(Map) has never been called for this index.

Parameters:

directory - where the index resides.

Returns:

commit userData.

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

See Also:

getCommitUserData()

getVersion

public long getVersion()

Version number when this IndexReader was opened. Not implemented in the IndexReader base class.

If this reader is based on a Directory (ie, was created by calling open(org.apache.lucene.store.Directory), or reopen() on a reader based on a Directory), then this method returns the version recorded in the commit that the reader opened. This version is advanced every time IndexWriter.commit(long) is called.

If instead this reader is a near real-time reader (ie, obtained by a call to IndexWriter.getReader(), or by calling reopen() on a near real-time reader), then this method returns the version of the last commit done by the writer. Note that even as further changes are made with the writer, the version will not changed until a commit is completed. Thus, you should not rely on this method to determine when a near real-time reader should be opened. Use isCurrent() instead.

Throws:

UnsupportedOperationException - unless overridden in subclass

getCommitUserData

public Map<String,String> getCommitUserData()

Retrieve the String userData optionally passed to IndexWriter#commit. This will return null if IndexWriter.commit(Map) has never been called for this index.

See Also:

getCommitUserData(Directory)

isCurrent

public boolean isCurrent()
                  throws CorruptIndexException,
                         IOException

Check whether any new changes have occurred to the index since this reader was opened.

If this reader is based on a Directory (ie, was created by calling open(org.apache.lucene.store.Directory), or reopen() on a reader based on a Directory), then this method checks if any further commits (see IndexWriter.commit(long) have occurred in that directory).

If instead this reader is a near real-time reader (ie, obtained by a call to IndexWriter.getReader(), or by calling reopen() on a near real-time reader), then this method checks if either a new commmit has occurred, or any new uncommitted changes have taken place via the writer. Note that even if the writer has only performed merging, this method will still return false.

In any event, if this returns false, you should call reopen() to get a new reader that sees the changes.

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

UnsupportedOperationException - unless overridden in subclass

isOptimized

public boolean isOptimized()

Checks is the index is optimized (if it has a single segment and no deletions). Not implemented in the IndexReader base class.

Returns:

true if the index is optimized; false otherwise

Throws:

UnsupportedOperationException - unless overridden in subclass

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. If the directory does not exist or if there is no index in it.

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 int numDeletedDocs()

Returns the number of deleted documents.

document

public Document document(int n)
                  throws CorruptIndexException,
                         IOException

Returns the stored fields of the n^th 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 n^th 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.

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)

setNorm

public void setNorm(int doc,
                    String field,
                    byte value)
             throws StaleReaderException,
                    CorruptIndexException,
                    LockObtainFailedException,
                    IOException

Expert: Resets the normalization factor for the named field of the named document. The norm represents the product of the field's boost and its length normalization. Thus, to preserve the length normalization values when resetting this, one should base the new value upon the old. NOTE: If this field does not store norms, then this method call will silently do nothing.

Throws:

StaleReaderException - if the index has changed since this reader was opened

CorruptIndexException - if the index is corrupt

LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)

IOException - if there is a low-level IO error

See Also:

norms(String), Similarity.decodeNorm(byte)

doSetNorm

protected abstract void doSetNorm(int doc,
                                  String field,
                                  byte value)
                           throws CorruptIndexException,
                                  IOException

Implements setNorm in subclass.

Throws:

CorruptIndexException

IOException

setNorm

public void setNorm(int doc,
                    String field,
                    float value)
             throws StaleReaderException,
                    CorruptIndexException,
                    LockObtainFailedException,
                    IOException

Expert: Resets the normalization factor for the named field of the named document.

Throws:

StaleReaderException - if the index has changed since this reader was opened

CorruptIndexException - if the index is corrupt

LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)

IOException - if there is a low-level IO error

See Also:

norms(String), Similarity.decodeNorm(byte)

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

termDocs

public abstract TermDocs termDocs()
                           throws IOException

Returns an unpositioned TermDocs enumerator.

Throws:

IOException - if there is a low-level IO error

termPositions

public 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, ... pos_freq-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

termPositions

public abstract TermPositions termPositions()
                                     throws IOException

Returns an unpositioned TermPositions enumerator.

Throws:

IOException - if there is a low-level IO error

deleteDocument

public void deleteDocument(int docNum)
                    throws StaleReaderException,
                           CorruptIndexException,
                           LockObtainFailedException,
                           IOException

Deletes the document numbered docNum. Once a document is deleted it will not appear in TermDocs or TermPostitions enumerations. Attempts to read its field with the document(int) method will result in an error. The presence of this document may still be reflected in the docFreq(org.apache.lucene.index.Term) statistic, though this will be corrected eventually as the index is further modified.

Throws:

StaleReaderException - if the index has changed since this reader was opened

CorruptIndexException - if the index is corrupt

LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)

IOException - if there is a low-level IO error

doDelete

protected abstract void doDelete(int docNum)
                          throws CorruptIndexException,
                                 IOException

Implements deletion of the document numbered docNum. Applications should call deleteDocument(int) or deleteDocuments(Term).

Throws:

CorruptIndexException

IOException

deleteDocuments

public int deleteDocuments(Term term)
                    throws StaleReaderException,
                           CorruptIndexException,
                           LockObtainFailedException,
                           IOException

Deletes all documents that have a given term indexed. This is useful if one uses a document field to hold a unique ID string for the document. Then to delete such a document, one merely constructs a term with the appropriate field and the unique ID string as its text and passes it to this method. See deleteDocument(int) for information about when this deletion will become effective.

Returns:

the number of documents deleted

Throws:

StaleReaderException - if the index has changed since this reader was opened

CorruptIndexException - if the index is corrupt

LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)

IOException - if there is a low-level IO error

undeleteAll

public void undeleteAll()
                 throws StaleReaderException,
                        CorruptIndexException,
                        LockObtainFailedException,
                        IOException

Undeletes all documents currently marked as deleted in this index.

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

doUndeleteAll

protected abstract void doUndeleteAll()
                               throws CorruptIndexException,
                                      IOException

Implements actual undeleteAll() in subclass.

Throws:

CorruptIndexException

IOException

acquireWriteLock

protected void acquireWriteLock()
                         throws IOException

Does nothing by default. Subclasses that require a write lock for index modifications must implement this method.

Throws:

IOException

flush

public final void flush()
                 throws IOException

Throws:

IOException

flush

public final void flush(Map<String,String> commitUserData)
                 throws IOException

Parameters:

commitUserData - Opaque Map (String -> String) that's recorded into the segments file in the index, and retrievable by getCommitUserData(org.apache.lucene.store.Directory).

Throws:

IOException

commit

protected final void commit()
                     throws IOException

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

public final void commit(Map<String,String> commitUserData)
                  throws IOException

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

doCommit

protected abstract void doCommit(Map<String,String> commitUserData)
                          throws IOException

Implements commit.

Throws:

IOException

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

getFieldNames

public abstract Collection<String> getFieldNames(IndexReader.FieldOption fldOption)

Get a list of unique field names that exist in this index and have the specified field option information.

Parameters:

fldOption - specifies which field option should be available for the returned fields

Returns:

Collection of Strings indicating the names of the fields.

See Also:

IndexReader.FieldOption

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.

WARNING: this API is new and experimental and may suddenly change.

Throws:

IOException

main

public static void main(String[] args)

Prints the filename and size of each file within a given compound file. Add the -extract flag to extract files to the current working directory. In order to make the extracted version of the index work, you have to copy the segments file from the compound index into the directory where the extracted files are stored.

Parameters:

args - Usage: org.apache.lucene.index.IndexReader [-extract] <cfsfile>

listCommits

public static Collection<IndexCommit> listCommits(Directory dir)
                                           throws IOException

Returns all commit points that exist in the Directory. Normally, because the default is KeepOnlyLastCommitDeletionPolicy, there would be only one commit point. But if you're using a custom IndexDeletionPolicy then there could be many commits. Once you have a given commit, you can open a reader on it by calling open(IndexCommit,boolean) There must be at least one commit in the Directory, else this method throws IOException. Note that if a commit is in progress while this method is running, that commit may or may not be returned array.

Throws:

IOException

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.

getFieldCacheKey

public Object getFieldCacheKey()

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.