org.apache.lucene.store

## Class FileSwitchDirectory

- java.lang.Object
- - org.apache.lucene.store.Directory
  - - org.apache.lucene.store.FileSwitchDirectory

- All Implemented Interfaces:
    Closeable, AutoCloseable

      public class FileSwitchDirectory
      extends Directory

  Expert: A Directory instance that switches files between two other Directory instances.

  Files with the specified extensions are placed in the primary directory; others are placed in the secondary directory. The provided Set must not change once passed to this class, and must allow multiple threads to call contains at once.

  Locks with a name having the specified extensions are delegated to the primary directory; others are delegated to the secondary directory. Ideally, both Directory instances should use the same lock factory.

  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `FileSwitchDirectory(Set<String> primaryExtensions, Directory primaryDir, Directory secondaryDir, boolean doClose)`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `close()` Closes the store.
    `IndexOutput` | `createOutput(String name, IOContext context)` Creates a new, empty file in the directory with the given name.
    `void` | `deleteFile(String name)` Removes an existing file in the directory.
    `long` | `fileLength(String name)` Returns the length of a file in the directory.
    `static String` | `getExtension(String name)` Utility method to return a file's extension.
    `Directory` | `getPrimaryDir()` Return the primary directory
    `Directory` | `getSecondaryDir()` Return the secondary directory
    `String[]` | `listAll()` Returns an array of strings, one for each entry in the directory.
    `Lock` | `obtainLock(String name)` Returns an obtained `Lock`.
    `IndexInput` | `openInput(String name, IOContext context)` Returns a stream reading an existing file.
    `void` | `renameFile(String source, String dest)` Renames `source` to `dest` as an atomic operation, where `dest` does not yet exist in the directory.
    `void` | `sync(Collection<String> names)` Ensure that any writes to these files are moved to stable storage.

    - ### Methods inherited from class org.apache.lucene.store.Directory

      `copyFrom, ensureOpen, openChecksumInput, toString`

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

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

- - ### Constructor Detail

    - #### FileSwitchDirectory

          public FileSwitchDirectory(Set<String> primaryExtensions,
                             Directory primaryDir,
                             Directory secondaryDir,
                             boolean doClose)

  - ### Method Detail

    - #### getPrimaryDir

          public Directory getPrimaryDir()

      Return the primary directory

    - #### getSecondaryDir

          public Directory getSecondaryDir()

      Return the secondary directory

    - #### obtainLock

          public Lock obtainLock(String name)
                          throws IOException

      Description copied from class: `Directory`
      Returns an obtained `Lock`.
      Specified by:
        `obtainLock` in class `Directory`
      Parameters:
        `name` - the name of the lock file
      Throws:
        `LockObtainFailedException` - (optional specific exception) if the lock could not be obtained because it is currently held elsewhere.
        `IOException` - if any i/o error occurs attempting to gain the lock

    - #### close

          public void close()
                     throws IOException

      Description copied from class: `Directory`
      Closes the store.
      Specified by:
        `close` in interface `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      Specified by:
        `close` in class `Directory`
      Throws:
        `IOException`

    - #### listAll

          public String[] listAll()
                           throws IOException

      Description copied from class: `Directory`
      Returns an array of strings, one for each entry in the directory.
      Specified by:
        `listAll` in class `Directory`
      Throws:
        `IOException` - in case of IO error

    - #### getExtension

          public static String getExtension(String name)

      Utility method to return a file's extension.

    - #### deleteFile

          public void deleteFile(String name)
                          throws IOException

      Description copied from class: `Directory`
      Removes an existing file in the directory.
      Specified by:
        `deleteFile` in class `Directory`
      Throws:
        `IOException`

    - #### fileLength

          public long fileLength(String name)
                          throws IOException

      Description copied from class: `Directory`
      Returns the length of a file in the directory. This method follows the following contract:
      - Throws `FileNotFoundException` or `NoSuchFileException` if the file does not exist.
      - Returns a value ≥0 if the file exists, which specifies its length.
      Specified by:
        `fileLength` in class `Directory`
      Parameters:
        `name` - the name of the file for which to return the length.
      Throws:
        `IOException` - if there was an IO error while retrieving the file's length.

    - #### createOutput

          public IndexOutput createOutput(String name,
                                 IOContext context)
                                   throws IOException

      Description copied from class: `Directory`
      Creates a new, empty file in the directory with the given name. Returns a stream writing this file.
      Specified by:
        `createOutput` in class `Directory`
      Throws:
        `IOException`

    - #### sync

          public void sync(Collection<String> names)
                    throws IOException

      Description copied from class: `Directory`
      Ensure that any writes to these files are moved to stable storage. Lucene uses this to properly commit changes to the index, to prevent a machine/OS crash from corrupting the index.
      NOTE: Clients may call this method for same files over and over again, so some impls might optimize for that. For other impls the operation can be a noop, for various reasons.
      Specified by:
        `sync` in class `Directory`
      Throws:
        `IOException`

    - #### renameFile

          public void renameFile(String source,
                        String dest)
                          throws IOException

      Description copied from class: `Directory`
      Renames `source` to `dest` as an atomic operation, where `dest` does not yet exist in the directory.

      Notes: This method is used by IndexWriter to publish commits. It is ok if this operation is not truly atomic, for example both `source` and `dest` can be visible temporarily. It is just important that the contents of `dest` appear atomically, or an exception is thrown.

      Specified by:
        `renameFile` in class `Directory`
      Throws:
        `IOException`

    - #### openInput

          public IndexInput openInput(String name,
                             IOContext context)
                               throws IOException

      Description copied from class: `Directory`
      Returns a stream reading an existing file.

      Throws `FileNotFoundException` or `NoSuchFileException` if the file does not exist.

      Specified by:
        `openInput` in class `Directory`
      Throws:
        `IOException`

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