org.apache.lucene.index
Class IndexReader

java.lang.Object
  |
  +--org.apache.lucene.index.IndexReader

public abstract class IndexReader

extends Object

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 the static method open(java.lang.String).

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.

Constructor Summary

protected

IndexReader(Directory directory)

Method Summary

void	close() Closes files associated with this index.
void	delete(int docNum) Deletes the document numbered docNum.
int	delete(Term term) Deletes all documents containing term.
abstract int	docFreq(Term t) Returns the number of documents containing the term t.
abstract Document	document(int n) Returns the stored fields of the nth Document in this index.
protected void	finalize() Release the write lock, if needed.
static boolean	indexExists(Directory directory) Returns true if an index exists at the specified directory.
static boolean	indexExists(File directory) Returns true if an index exists at the specified directory.
static boolean	indexExists(String directory) Returns true if an index exists at the specified directory.
abstract boolean	isDeleted(int n) Returns true if document n has been deleted
static boolean	isLocked(Directory directory) Returns true iff the index in the named directory is currently locked.
static boolean	isLocked(String directory) Returns true iff the index in the named directory is currently locked.
static long	lastModified(Directory directory) Returns the time the index in this directory was last modified.
static long	lastModified(File directory) Returns the time the index in the named directory was last modified.
static long	lastModified(String directory) Returns the time the index in the named directory was last modified.
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 int	numDocs() Returns the number of documents in this index.
static IndexReader	open(Directory directory) Returns an IndexReader reading the index in the given Directory.
static IndexReader	open(File path) Returns an IndexReader reading the index in an FSDirectory in the named path.
static IndexReader	open(String path) Returns an IndexReader reading the index in an FSDirectory in the named path.
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 after a given term.
static void	unlock(Directory directory) Forcibly unlocks the index in the named directory.

Methods inherited from class java.lang.Object

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

Constructor Detail

IndexReader

protected IndexReader(Directory directory)

Method Detail

open

public static IndexReader open(String path)
                        throws IOException

Returns an IndexReader reading the index in an FSDirectory in the named path.

open

public static IndexReader open(File path)
                        throws IOException

Returns an IndexReader reading the index in an FSDirectory in the named path.

open

public static IndexReader open(Directory directory)
                        throws IOException

Returns an IndexReader reading the index in the given Directory.

lastModified

public static long lastModified(String directory)
                         throws IOException

Returns the time the index in the named directory was last modified.

lastModified

public static long lastModified(File directory)
                         throws IOException

Returns the time the index in the named directory was last modified.

lastModified

public static long lastModified(Directory directory)
                         throws IOException

Returns the time the index in this directory was last modified.

indexExists

public static boolean indexExists(String directory)

Returns true if an index exists at the specified directory. If the directory does not exist or if there is no index in it. false is returned.

Parameters:

directory - the directory to check for an index

Returns:

true if an index exists; false otherwise

indexExists

public static boolean indexExists(File directory)

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

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.

document

public abstract Document document(int n)
                           throws IOException

Returns the stored fields of the n^th Document in this index.

isDeleted

public abstract boolean isDeleted(int n)

Returns true if document n has been deleted

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.

See Also:

Similarity.norm(int)

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.

terms

public abstract TermEnum terms(Term t)
                        throws IOException

Returns an enumeration of all terms after a given term. The enumeration is ordered by Term.compareTo(). Each term is greater than all that precede it in the enumeration.

docFreq

public abstract int docFreq(Term t)
                     throws IOException

Returns the number of documents containing the term t.

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. 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.

termDocs

public abstract TermDocs termDocs()
                           throws IOException

Returns an unpositioned TermDocs enumerator.

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 faciliates phrase and proximity searching.

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

termPositions

public abstract TermPositions termPositions()
                                     throws IOException

Returns an unpositioned TermPositions enumerator.

delete

public final void delete(int docNum)
                  throws 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.

delete

public final int delete(Term term)
                 throws IOException

Deletes all documents containing term. 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. Returns the number of documents 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.

finalize

protected final void finalize()
                       throws IOException

Release the write lock, if needed.

Overrides:

finalize in class Object

isLocked

public static boolean isLocked(Directory directory)
                        throws IOException

Returns true iff the index in the named directory is currently locked.

Parameters:

directory - the directory to check for a lock

Throws:

IOException - if there is a problem with accessing the index

isLocked

public static boolean isLocked(String directory)
                        throws IOException

Returns true iff the index in the named directory is currently locked.

Parameters:

directory - the directory to check for a lock

Throws:

IOException - if there is a problem with accessing the index

unlock

public static void unlock(Directory directory)
                   throws IOException

Forcibly unlocks the index in the named directory.

Caution: this should only be used by failure recovery code, when it is known that no other process nor thread is in fact currently accessing this index.