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org.apache.lucene.index
abstract public class: IndexReader [javadoc | source]
java.lang.Object
   org.apache.lucene.index.IndexReader

All Implemented Interfaces:
    Cloneable, Closeable

Direct Known Subclasses:
    SegmentReader, ReadOnlySegmentReader, DirectoryReader, ReadOnlyMultiSegmentReader, MultiReader, FakeReader, GCJSegmentReader, ReadOnlyDirectoryReader, ParallelReader, FakeDeleteIndexReader, OneNormsReader, MultiSegmentReader, FilterIndexReader, DirectoryIndexReader, TestReader, MemoryIndexReader, InstantiatedIndexReader

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:
public static final class  IndexReader.FieldOption  Constants describing field properties, for example used for {@link IndexReader#getFieldNames(FieldOption)}. 
Field Summary
protected  boolean hasChanges     
static  int DEFAULT_TERMS_INDEX_DIVISOR     
Constructor:
 protected IndexReader() 
Method from org.apache.lucene.index.IndexReader Summary:
acquireWriteLock,   clone,   clone,   close,   commit,   commit,   decRef,   deleteDocument,   deleteDocuments,   directory,   doClose,   doCommit,   doDelete,   doSetNorm,   doUndeleteAll,   docFreq,   document,   document,   ensureOpen,   flush,   flush,   getCommitUserData,   getCommitUserData,   getCurrentVersion,   getFieldCacheKey,   getFieldNames,   getIndexCommit,   getRefCount,   getSequentialSubReaders,   getTermFreqVector,   getTermFreqVector,   getTermFreqVector,   getTermFreqVectors,   getTermInfosIndexDivisor,   getUniqueTermCount,   getVersion,   hasDeletions,   hasNorms,   incRef,   indexExists,   isCurrent,   isDeleted,   isOptimized,   lastModified,   listCommits,   main,   maxDoc,   norms,   norms,   numDeletedDocs,   numDocs,   open,   open,   open,   open,   open,   open,   open,   reopen,   reopen,   reopen,   setNorm,   setNorm,   termDocs,   termDocs,   termPositions,   termPositions,   terms,   terms,   undeleteAll
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from org.apache.lucene.index.IndexReader Detail:
 protected synchronized  void acquireWriteLock() throws IOException 
    Does nothing by default. Subclasses that require a write lock for index modifications must implement this method.
 public synchronized 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.

 public synchronized IndexReader clone(boolean openReadOnly) throws CorruptIndexException, IOException 
    Clones the IndexReader and optionally changes readOnly. A readOnly reader cannot open a writeable reader.
 public final synchronized  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.
 protected final synchronized  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).
 public final synchronized  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).
 public synchronized  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.
 public synchronized  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 method will result in an error. The presence of this document may still be reflected in the #docFreq statistic, though this will be corrected eventually as the index is further modified.
 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.
 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.
 abstract protected  void doClose() throws IOException
    Implements close.
 abstract protected  void doCommit(Map<String, String> commitUserData) throws IOException
    Implements commit. NOTE: subclasses should override this. In 3.0 this will become an abstract method.
 abstract protected  void doDelete(int docNum) throws CorruptIndexException, IOException
 abstract protected  void doSetNorm(int doc,
    String field,
    byte value) throws CorruptIndexException, IOException
    Implements setNorm in subclass.
 abstract protected  void doUndeleteAll() throws CorruptIndexException, IOException
    Implements actual undeleteAll() in subclass.
 abstract public int docFreq(Term t) throws IOException
    Returns the number of documents containing the term t.
 public Document document(int n) throws CorruptIndexException, IOException 
    Returns the stored fields of the nth Document in this index.

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

 abstract public Document document(int n,
    FieldSelector fieldSelector) throws CorruptIndexException, IOException
    Get the org.apache.lucene.document.Document at the n th position. The FieldSelector may be used to determine what org.apache.lucene.document.Field s to load and how they should be loaded. NOTE: If this Reader (more specifically, the underlying FieldsReader) is closed before the lazy org.apache.lucene.document.Field is loaded an exception may be thrown. If you want the value of a lazy org.apache.lucene.document.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.

 protected final  void ensureOpen() throws AlreadyClosedException 
 public final synchronized  void flush() throws IOException 
 public final synchronized  void flush(Map<String, String> commitUserData) throws IOException 
 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.
 public static Map<String, String> getCommitUserData(Directory directory) throws CorruptIndexException, IOException 
 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.
 public Object getFieldCacheKey() 
    Expert
 abstract public Collection<String> getFieldNames(FieldOption fldOption)
    Get a list of unique field names that exist in this index and have the specified field option information.
 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.

 public synchronized int getRefCount() 
    Expert: returns the current refCount for this reader
 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 . Use the parent reader directly.

 abstract public 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.
 abstract public  void getTermFreqVector(int docNumber,
    TermVectorMapper mapper) throws IOException
    Map all the term vectors for all fields in a Document
 abstract public  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 .
 abstract public 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.
 public int getTermInfosIndexDivisor() 
    For IndexReader implementations that use TermInfosReader to read terms, this returns the current indexDivisor as specified when the reader was opened.
 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.
 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 , 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 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.

 abstract public boolean hasDeletions()
    Returns true if any documents have been deleted
 public boolean hasNorms(String field) throws IOException 
    Returns true if there are norms stored for this field.
 public synchronized  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.
 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.
 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 , or #reopen on a reader based on a Directory), then this method checks if any further commits (see IndexWriter#commit 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.

 abstract public boolean isDeleted(int n)
    Returns true if document n has been deleted
 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.
 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.
 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 IndexReader#open(IndexCommit,boolean) There must be at least one commit in the Directory, else this method throws java.io.IOException . Note that if a commit is in progress while this method is running, that commit may or may not be returned array.
 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.
 abstract public 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.
 abstract public 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.
 abstract public  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.
 public int numDeletedDocs() 
    Returns the number of deleted documents.
 abstract public int numDocs()
    Returns the number of documents in this index.
 public static IndexReader open(Directory directory) throws CorruptIndexException, IOException 
    Returns a IndexReader reading the index in the given Directory, with readOnly=true.
 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.
 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.
 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.
 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.
 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.
 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.
 public synchronized 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.

 public synchronized 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.
 public synchronized 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.
 public synchronized  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.
 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.
 abstract public TermDocs termDocs() throws IOException
    Returns an unpositioned TermDocs enumerator.
 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.

 abstract public TermPositions termPositions() throws IOException
 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, ... posfreq-1> >*

    This positional information facilitates phrase and proximity searching.

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

 abstract public 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() .
 abstract public 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.
 public synchronized  void undeleteAll() throws StaleReaderException, CorruptIndexException, LockObtainFailedException, IOException 
    Undeletes all documents currently marked as deleted in this index.