org.apache.lucene.index

## Class StandardDirectoryReader

- java.lang.Object
- - org.apache.lucene.index.IndexReader
  - - org.apache.lucene.index.CompositeReader
    - - org.apache.lucene.index.BaseCompositeReader<LeafReader>
      - - org.apache.lucene.index.DirectoryReader
        - - org.apache.lucene.index.StandardDirectoryReader

- All Implemented Interfaces:
    Closeable, AutoCloseable

      public final class StandardDirectoryReader
      extends DirectoryReader

  Default implementation of `DirectoryReader`.

- - ### Nested Class Summary

    - ### Nested classes/interfaces inherited from class org.apache.lucene.index.IndexReader

      `IndexReader.CacheHelper, IndexReader.CacheKey, IndexReader.ClosedListener`

  - ### Field Summary

    - ### Fields inherited from class org.apache.lucene.index.DirectoryReader

      `directory`

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `doClose()` Implements close.
    `protected DirectoryReader` | `doOpenIfChanged()` Implement this method to support `DirectoryReader.openIfChanged(DirectoryReader)`.
    `protected DirectoryReader` | `doOpenIfChanged(IndexCommit commit)` Implement this method to support `DirectoryReader.openIfChanged(DirectoryReader,IndexCommit)`.
    `protected DirectoryReader` | `doOpenIfChanged(IndexWriter writer, boolean applyAllDeletes)` Implement this method to support `DirectoryReader.openIfChanged(DirectoryReader,IndexWriter,boolean)`.
    `IndexCommit` | `getIndexCommit()` Expert: return the IndexCommit that this reader has opened.
    `IndexReader.CacheHelper` | `getReaderCacheHelper()` Optional method: Return a `IndexReader.CacheHelper` that can be used to cache based on the content of this reader.
    `SegmentInfos` | `getSegmentInfos()` Return the `SegmentInfos` for this reader.
    `long` | `getVersion()` Version number when this IndexReader was opened.
    `boolean` | `isCurrent()` Check whether any new changes have occurred to the index since this reader was opened.
    `static DirectoryReader` | `open(Directory directory, SegmentInfos infos, List<? extends LeafReader> oldReaders, Map<String,String> readerAttributes)` This constructor is only used for `doOpenIfChanged(SegmentInfos)`, as well as NRT replication.
    `String` | `toString()`

    - ### Methods inherited from class org.apache.lucene.index.DirectoryReader

      `directory, indexExists, listCommits, open, open, open, open, open, open, openIfChanged, openIfChanged, openIfChanged, openIfChanged`

    - ### Methods inherited from class org.apache.lucene.index.BaseCompositeReader

      `docFreq, document, getDocCount, getSequentialSubReaders, getSumDocFreq, getSumTotalTermFreq, getTermVectors, maxDoc, numDocs, readerBase, readerIndex, totalTermFreq`

    - ### Methods inherited from class org.apache.lucene.index.CompositeReader

      `getContext`

    - ### Methods inherited from class org.apache.lucene.index.IndexReader

      `close, decRef, document, document, ensureOpen, equals, getRefCount, getTermVector, hasDeletions, hashCode, incRef, leaves, numDeletedDocs, registerParentReader, tryIncRef`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Method Detail

    - #### open

          public static DirectoryReader open(Directory directory,
                                             SegmentInfos infos,
                                             List<? extends LeafReader> oldReaders,
                                             Map<String,String> readerAttributes)
                                      throws IOException

      This constructor is only used for `doOpenIfChanged(SegmentInfos)`, as well as NRT replication.
      Throws:
        `IOException`
      NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `CompositeReader`

    - #### doOpenIfChanged

          protected DirectoryReader doOpenIfChanged()
                                             throws IOException

      Description copied from class: `DirectoryReader`
      Implement this method to support `DirectoryReader.openIfChanged(DirectoryReader)`. If this reader does not support reopen, return `null`, so client code is happy. This should be consistent with `DirectoryReader.isCurrent()` (should always return `true`) if reopen is not supported.
      Specified by:
        `doOpenIfChanged` in class `DirectoryReader`
      Returns:
        null if there are no changes; else, a new DirectoryReader instance.
      Throws:
        `IOException` - if there is a low-level IO error

    - #### doOpenIfChanged

          protected DirectoryReader doOpenIfChanged(IndexCommit commit)
                                             throws IOException

      Description copied from class: `DirectoryReader`
      Implement this method to support `DirectoryReader.openIfChanged(DirectoryReader,IndexCommit)`. If this reader does not support reopen from a specific `IndexCommit`, throw `UnsupportedOperationException`.
      Specified by:
        `doOpenIfChanged` in class `DirectoryReader`
      Returns:
        null if there are no changes; else, a new DirectoryReader instance.
      Throws:
        `IOException` - if there is a low-level IO error

    - #### doOpenIfChanged

          protected DirectoryReader doOpenIfChanged(IndexWriter writer,
                                                    boolean applyAllDeletes)
                                             throws IOException

      Description copied from class: `DirectoryReader`
      Implement this method to support `DirectoryReader.openIfChanged(DirectoryReader,IndexWriter,boolean)`. If this reader does not support reopen from `IndexWriter`, throw `UnsupportedOperationException`.
      Specified by:
        `doOpenIfChanged` in class `DirectoryReader`
      Returns:
        null if there are no changes; else, a new DirectoryReader instance.
      Throws:
        `IOException` - if there is a low-level IO error

    - #### getVersion

          public long getVersion()

      Description copied from class: `DirectoryReader`
      Version number when this IndexReader was opened.

      This method returns the version recorded in the commit that the reader opened. This version is advanced every time a change is made with `IndexWriter`.

      Specified by:
        `getVersion` in class `DirectoryReader`

    - #### getSegmentInfos

          public SegmentInfos getSegmentInfos()

      Return the `SegmentInfos` for this reader.
      NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

    - #### isCurrent

          public boolean isCurrent()
                            throws IOException

      Description copied from class: `DirectoryReader`
      Check whether any new changes have occurred to the index since this reader was opened.

      If this reader was created by calling `DirectoryReader.open(org.apache.lucene.store.Directory)`, then this method checks if any further commits (see `IndexWriter.commit()`) have occurred in the directory.

      If instead this reader is a near real-time reader (ie, obtained by a call to `DirectoryReader.open(IndexWriter)`, or by calling `DirectoryReader.openIfChanged(org.apache.lucene.index.DirectoryReader)` on a near real-time reader), then this method checks if either a new commit 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 `DirectoryReader.openIfChanged(org.apache.lucene.index.DirectoryReader)` to get a new reader that sees the changes.

      Specified by:
        `isCurrent` in class `DirectoryReader`
      Throws:
        `IOException` - if there is a low-level IO error

    - #### doClose

          protected void doClose()
                          throws IOException

      Description copied from class: `IndexReader`
      Implements close.
      Specified by:
        `doClose` in class `IndexReader`
      Throws:
        `IOException`

    - #### getIndexCommit

          public IndexCommit getIndexCommit()
                                     throws IOException

      Description copied from class: `DirectoryReader`
      Expert: return the IndexCommit that this reader has opened.
      Specified by:
        `getIndexCommit` in class `DirectoryReader`
      Throws:
        `IOException`

    - #### getReaderCacheHelper

          public IndexReader.CacheHelper getReaderCacheHelper()

      Description copied from class: `IndexReader`
      Optional method: Return a `IndexReader.CacheHelper` that can be used to cache based on the content of this reader. Two readers that have different data or different sets of deleted documents will be considered different.

      A return value of `null` indicates that this reader is not suited for caching, which is typically the case for short-lived wrappers that alter the content of the wrapped reader.

      Specified by:
        `getReaderCacheHelper` in class `IndexReader`

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