Package org.apache.lucene.index

Class CompositeReader

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    Direct Known Subclasses:
    BaseCompositeReader
    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 DirectoryReader.open() methods, e.g. DirectoryReader.open(Directory). 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. DirectoryReader.open(Directory).

    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.

    • Constructor Detail

      • CompositeReader

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

    • Method Detail

      • getSequentialSubReaders

        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:
        IndexReader.leaves()

      • getContext

        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