Class CompositeReader

  extended by org.apache.lucene.index.IndexReader
      extended by org.apache.lucene.index.CompositeReader
All Implemented Interfaces:
Direct Known Subclasses:

public abstract class CompositeReader
extends IndexReader

Instances of this reader type 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 AtomicReaderContext for all sub-readers via IndexReader.leaves(). 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 methods, e.g. DirectoryReader implements the CompositeReader interface, it is not possible to directly get postings.

Concrete subclasses of IndexReader are usually constructed with a call to one of the static open() methods, e.g.

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/interfaces inherited from class org.apache.lucene.index.IndexReader
Constructor Summary
protected CompositeReader()
          Sole constructor.
Method Summary
 CompositeReaderContext getContext()
          Expert: Returns the root IndexReaderContext for this IndexReader's sub-reader tree.
protected abstract  List<? extends IndexReader> getSequentialSubReaders()
          Expert: returns the sequential sub readers that this reader is logically composed of.
 String toString()
Methods inherited from class org.apache.lucene.index.IndexReader
addReaderClosedListener, close, decRef, docFreq, doClose, document, document, document, ensureOpen, equals, getCombinedCoreAndDeletesKey, getCoreCacheKey, getRefCount, getTermVector, getTermVectors, hasDeletions, hashCode, incRef, leaves, maxDoc, numDeletedDocs, numDocs, open, open, open, open, open, registerParentReader, removeReaderClosedListener, totalTermFreq, tryIncRef
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail


protected CompositeReader()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail


public String toString()
toString in class Object


protected abstract List<? extends IndexReader> getSequentialSubReaders()
Expert: returns the sequential sub readers that this reader is logically composed of. This method may not return null.

NOTE: In contrast to previous Lucene versions this method is no longer public, code that wants to get all AtomicReaders this composite is composed of should use IndexReader.leaves().

See Also:


public final CompositeReaderContext getContext()
Description copied from class: IndexReader
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.

Specified by:
getContext in class IndexReader

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