org.apache.lucene.index

## Class FilterDirectoryReader

- 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.FilterDirectoryReader

- All Implemented Interfaces:
    Closeable, AutoCloseable
  Direct Known Subclasses:
    ExitableDirectoryReader

      public abstract class FilterDirectoryReader
      extends DirectoryReader

  A FilterDirectoryReader wraps another DirectoryReader, allowing implementations to transform or extend it. Subclasses should implement doWrapDirectoryReader to return an instance of the subclass. If the subclass wants to wrap the DirectoryReader's subreaders, it should also implement a SubReaderWrapper subclass, and pass an instance to its super constructor.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `FilterDirectoryReader.SubReaderWrapper` Factory class passed to FilterDirectoryReader constructor that allows subclasses to wrap the filtered DirectoryReader's subreaders.

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

      `IndexReader.ReaderClosedListener`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected DirectoryReader` | `in` The filtered DirectoryReader

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

      `directory`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `FilterDirectoryReader(DirectoryReader in, FilterDirectoryReader.SubReaderWrapper wrapper)` Create a new FilterDirectoryReader that filters a passed in DirectoryReader, using the supplied SubReaderWrapper to wrap its subreader.

  - ### Method Summary

    All Methods Static Methods Instance Methods Abstract 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)`.
    `protected abstract DirectoryReader` | `doWrapDirectoryReader(DirectoryReader in)` Called by the doOpenIfChanged() methods to return a new wrapped DirectoryReader.
    `DirectoryReader` | `getDelegate()` Returns the wrapped `DirectoryReader`.
    `IndexCommit` | `getIndexCommit()` Expert: return the IndexCommit that this reader has opened.
    `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` | `unwrap(DirectoryReader reader)` Get the wrapped instance by `reader` as long as this reader is an instance of `FilterDirectoryReader`.

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

      `directory, indexExists, listCommits, 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, toString`

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

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

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

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

- - ### Field Detail

    - #### in

          protected final DirectoryReader in

      The filtered DirectoryReader

  - ### Constructor Detail

    - #### FilterDirectoryReader

          public FilterDirectoryReader(DirectoryReader in,
                                       FilterDirectoryReader.SubReaderWrapper wrapper)
                                throws IOException

      Create a new FilterDirectoryReader that filters a passed in DirectoryReader, using the supplied SubReaderWrapper to wrap its subreader.
      Parameters:
        `in` - the DirectoryReader to filter
        `wrapper` - the SubReaderWrapper to use to wrap subreaders
      Throws:
        `IOException`

  - ### Method Detail

    - #### unwrap

          public static DirectoryReader unwrap(DirectoryReader reader)

      Get the wrapped instance by `reader` as long as this reader is an instance of `FilterDirectoryReader`.

    - #### doWrapDirectoryReader

          protected abstract DirectoryReader doWrapDirectoryReader(DirectoryReader in)
                                                            throws IOException

      Called by the doOpenIfChanged() methods to return a new wrapped DirectoryReader. Implementations should just return an instantiation of themselves, wrapping the passed in DirectoryReader.
      Parameters:
        `in` - the DirectoryReader to wrap
      Returns:
        the wrapped DirectoryReader
      Throws:
        `IOException`

    - #### doOpenIfChanged

          protected final 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 final 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 final 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`

    - #### 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

    - #### 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`

    - #### doClose

          protected void doClose()
                          throws IOException

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

    - #### getDelegate

          public DirectoryReader getDelegate()

      Returns the wrapped `DirectoryReader`.

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