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 IndexInputs, 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:

  • 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

      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:

    • 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:

    • 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 IndexInputs, 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, ReadAdvice readAdvice) throws IOException
      Create a slice with a specific ReadAdvice. This is typically used by CompoundFormat implementations to honor the ReadAdvice of each file within the compound file.

      NOTE: it is only legal to call this method if this IndexInput has been open with ReadAdvice.NORMAL. However, this method accepts any ReadAdvice value but null as a read advice for the slice.

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

      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

    • updateReadAdvice

      public void updateReadAdvice(ReadAdvice readAdvice) throws IOException
      Optional method: Give a hint to this input about the change in 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.