Package org.apache.lucene.store

# Class IndexInput

java.lang.Object
org.apache.lucene.store.DataInput
org.apache.lucene.store.IndexInput

All Implemented Interfaces:
  `Closeable`, `AutoCloseable`, `Cloneable`

Direct Known Subclasses:
  `BufferedIndexInput`, `ByteBuffersIndexInput`, `ChecksumIndexInput`, `FilterIndexInput`

public abstract class IndexInput extends DataInput implements Closeable
Abstract base class for input from a file in a `Directory`. A random-access input stream. Used for all Lucene index input operations.

`IndexInput` may only be used from one thread, because it is not thread safe (it keeps internal state like file position). To allow multithreaded use, every `IndexInput` instance must be cloned before it is used in another thread. Subclasses must therefore implement `clone()`, returning a new `IndexInput` which operates on the same underlying resource, but positioned independently.

Warning: Lucene never closes cloned `IndexInput`s, it will only call `close()` on the original object.

If you access the cloned IndexInput after closing the original object, any `readXXX` methods will throw `AlreadyClosedException`.

See Also:
  - `Directory`

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `IndexInput(String resourceDescription)`
  resourceDescription should be a non-null, opaque string describing this resource; it's returned from `toString()`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `IndexInput`
  `clone()`
  Returns a clone of this stream.
  `abstract void`
  `close()`
  Closes the stream to further operations.
  `abstract long`
  `getFilePointer()`
  Returns the current position in this file, where the next read will occur.
  `protected String`
  `getFullSliceDescription(String sliceDescription)`
  Subclasses call this to get the String for resourceDescription of a slice of this `IndexInput`.
  `Optional<Boolean>`
  `isLoaded()`
  Returns a hint whether all the contents of this input are resident in physical memory.
  `abstract long`
  `length()`
  The number of bytes in the file.
  `void`
  `prefetch(long offset, long length)`
  Optional method: Give a hint to this input that some bytes will be read in the near future.
  `RandomAccessInput`
  `randomAccessSlice(long offset, long length)`
  Creates a random-access slice of this index input, with the given offset and length.
  `abstract void`
  `seek(long pos)`
  Sets current position in this file, where the next read will occur.
  `void`
  `skipBytes(long numBytes)`
  Skip over `numBytes` bytes.
  `abstract IndexInput`
  `slice(String sliceDescription, long offset, long length)`
  Creates a slice of this index input, with the given description, offset, and length.
  `IndexInput`
  `slice(String sliceDescription, long offset, long length, IOContext context)`
  Create a slice with a new `IOContext`.
  `String`
  `toString()`
  `void`
  `updateIOContext(IOContext context)`
  Optional method: Updates the `IOContext` to specify a new read access pattern.

  ### Methods inherited from class org.apache.lucene.store.DataInput

  `readByte, readBytes, readBytes, readFloats, readGroupVInt, readInt, readInts, readLong, readLongs, readMapOfStrings, readSetOfStrings, readShort, readString, readVInt, readVLong, readZInt, readZLong`

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

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

- ## Constructor Details

  - ### IndexInput

    protected IndexInput(String resourceDescription)
    resourceDescription should be a non-null, opaque string describing this resource; it's returned from `toString()`.

- ## Method Details

  - ### close

    public abstract void close() throws IOException
    Closes the stream to further operations.
    Specified by:
      `close` in interface `AutoCloseable`
    Specified by:
      `close` in interface `Closeable`
    Throws:
      `IOException`

  - ### getFilePointer

    public abstract long getFilePointer()
    Returns the current position in this file, where the next read will occur.
    See Also:
      - `seek(long)`

  - ### seek

    public abstract void seek(long pos) throws IOException
    Sets current position in this file, where the next read will occur. If this is beyond the end of the file then this will throw `EOFException` and then the stream is in an undetermined state.
    Throws:
      `IOException`
    See Also:
      - `getFilePointer()`

  - ### skipBytes

    public void skipBytes(long numBytes) throws IOException
    Skip over `numBytes` bytes. This method may skip bytes in whatever way is most optimal, and may not have the same behavior as reading the skipped bytes. In general, negative `numBytes` are not supported.

    Behavior is functionally equivalent to seeking to `getFilePointer() + numBytes`.

    Specified by:
      `skipBytes` in class `DataInput`
    Throws:
      `IOException`
    See Also:
      - `getFilePointer()`
      - `seek(long)`

  - ### length

    public abstract long length()
    The number of bytes in the file.

  - ### toString

    public String toString()
    Overrides:
      `toString` in class `Object`

  - ### clone

    public IndexInput clone()
    Returns a clone of this stream.

    Clones of a stream access the same data, and are positioned at the same point as the stream they were cloned from.

    Expert: Subclasses must ensure that clones may be positioned at different points in the input from each other and from the stream they were cloned from.

    Warning: Lucene never closes cloned `IndexInput`s, it will only call `close()` on the original object.

    If you access the cloned IndexInput after closing the original object, any `readXXX` methods will throw `AlreadyClosedException`.

    This method is NOT thread safe, so if the current `IndexInput` is being used by one thread while `clone` is called by another, disaster could strike.

    Overrides:
      `clone` in class `DataInput`

  - ### slice

    public abstract IndexInput slice(String sliceDescription, long offset, long length) throws IOException
    Creates a slice of this index input, with the given description, offset, and length. The slice is sought to the beginning.
    Throws:
      `IOException`

  - ### slice

    public IndexInput slice(String sliceDescription, long offset, long length, IOContext context) throws IOException
    Create a slice with a new `IOContext`. This is typically used by `CompoundFormat` implementations to modify the `IOContext` for specific files within the compound file.

    NOTE: only certain `IOContext` may be usable here, depending on how this instance was opened.

    The default implementation delegates to `slice(String, long, long)` and ignores the `IOContext`.

    Throws:
      `IOException`

  - ### getFullSliceDescription

    protected String getFullSliceDescription(String sliceDescription)
    Subclasses call this to get the String for resourceDescription of a slice of this `IndexInput`.

  - ### randomAccessSlice

    public RandomAccessInput randomAccessSlice(long offset, long length) throws IOException
    Creates a random-access slice of this index input, with the given offset and length.

    The default implementation calls `slice(java.lang.String, long, long)`, and it doesn't support random access, it implements absolute reads as seek+read.

    Throws:
      `IOException`

  - ### prefetch

    public void prefetch(long offset, long length) throws IOException
    Optional method: Give a hint to this input that some bytes will be read in the near future. IndexInput implementations may take advantage of this hint to start fetching pages of data immediately from storage.

    The default implementation is a no-op.

    Parameters:
      `offset` - start offset
      `length` - the number of bytes to prefetch
    Throws:
      `IOException`

  - ### updateIOContext

    public void updateIOContext(IOContext context) throws IOException
    Optional method: Updates the `IOContext` to specify a new read access pattern. IndexInput implementations may take advantage of this hint to optimize reads from storage.

    The default implementation is a no-op.

    Throws:
      `IOException`

  - ### isLoaded

    public Optional<Boolean> isLoaded()
    Returns a hint whether all the contents of this input are resident in physical memory. It's a hint because the operating system may have paged out some of the data by the time this method returns. If the optional is true, then it's likely that the contents of this input are resident in physical memory. A value of false does not imply that the contents are not resident in physical memory. An empty optional is returned if it is not possible to determine.

    This runs in linear time with the `length()` of this input / page size.

    The default implementation returns an empty optional.