## org.apache.lucene.index
Class FilterDirectoryReader

    java.lang.Object
      org.apache.lucene.index.IndexReader
          org.apache.lucene.index.CompositeReader
              org.apache.lucene.index.BaseCompositeReader<AtomicReader>
                  org.apache.lucene.index.DirectoryReader
                      org.apache.lucene.index.FilterDirectoryReader

All Implemented Interfaces:
  Closeable

    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
`static class` `FilterDirectoryReader.StandardReaderWrapper` A no-op SubReaderWrapper that simply returns the parent DirectoryReader's original subreaders.
`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
`protected DirectoryReader` `in` The filtered DirectoryReader

Fields inherited from class org.apache.lucene.index.DirectoryReader
`DEFAULT_TERMS_INDEX_DIVISOR, directory`

Constructor Summary
`FilterDirectoryReader(DirectoryReader in)` Create a new FilterDirectoryReader that filters a passed in DirectoryReader.
`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
`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.
`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.

Methods inherited from class org.apache.lucene.index.DirectoryReader
`directory, indexExists, listCommits, open, open, open, open, open, 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)

  Create a new FilterDirectoryReader that filters a passed in DirectoryReader.

  Parameters:
    `in` - the DirectoryReader to filter

### FilterDirectoryReader

    public FilterDirectoryReader(DirectoryReader in,
                                 FilterDirectoryReader.SubReaderWrapper wrapper)

  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

Method Detail

### doWrapDirectoryReader

    protected abstract DirectoryReader doWrapDirectoryReader(DirectoryReader in)

  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

### 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,boolean)`, 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`

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