Class IndexInput
- All Implemented Interfaces:
Closeable,AutoCloseable,Cloneable
- Direct Known Subclasses:
BufferedIndexInput,ByteBuffersIndexInput,ChecksumIndexInput,FilterIndexInput
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:
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Constructor Summary
ConstructorsModifierConstructorDescriptionprotectedIndexInput(String resourceDescription) resourceDescription should be a non-null, opaque string describing this resource; it's returned fromtoString(). -
Method Summary
Modifier and TypeMethodDescriptionclone()Returns a clone of this stream.abstract voidclose()Closes the stream to further operations.abstract longReturns the current position in this file, where the next read will occur.protected StringgetFullSliceDescription(String sliceDescription) Subclasses call this to get the String for resourceDescription of a slice of thisIndexInput.isLoaded()Returns a hint whether all the contents of this input are resident in physical memory.abstract longlength()The number of bytes in the file.voidprefetch(long offset, long length) Optional method: Give a hint to this input that some bytes will be read in the near future.randomAccessSlice(long offset, long length) Creates a random-access slice of this index input, with the given offset and length.abstract voidseek(long pos) Sets current position in this file, where the next read will occur.voidskipBytes(long numBytes) Skip overnumBytesbytes.abstract IndexInputCreates a slice of this index input, with the given description, offset, and length.slice(String sliceDescription, long offset, long length, ReadAdvice readAdvice) Create a slice with a specificReadAdvice.toString()voidupdateReadAdvice(ReadAdvice readAdvice) Optional method: Give a hint to this input about the change in 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
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Constructor Details
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IndexInput
resourceDescription should be a non-null, opaque string describing this resource; it's returned fromtoString().
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Method Details
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close
Closes the stream to further operations.- Specified by:
closein interfaceAutoCloseable- Specified by:
closein interfaceCloseable- Throws:
IOException
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getFilePointer
public abstract long getFilePointer()Returns the current position in this file, where the next read will occur.- See Also:
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seek
Sets current position in this file, where the next read will occur. If this is beyond the end of the file then this will throwEOFExceptionand then the stream is in an undetermined state.- Throws:
IOException- See Also:
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skipBytes
Skip overnumBytesbytes. 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, negativenumBytesare not supported.Behavior is functionally equivalent to seeking to
getFilePointer() + numBytes.- Specified by:
skipBytesin classDataInput- Throws:
IOException- See Also:
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length
public abstract long length()The number of bytes in the file. -
toString
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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 callclose()on the original object.If you access the cloned IndexInput after closing the original object, any
readXXXmethods will throwAlreadyClosedException.This method is NOT thread safe, so if the current
IndexInputis being used by one thread whilecloneis called by another, disaster could strike. -
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
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slice
public IndexInput slice(String sliceDescription, long offset, long length, ReadAdvice readAdvice) throws IOException Create a slice with a specificReadAdvice. This is typically used byCompoundFormatimplementations to honor theReadAdviceof each file within the compound file.NOTE: it is only legal to call this method if this
IndexInputhas been open withReadAdvice.NORMAL. However, this method accepts anyReadAdvicevalue butnullas a read advice for the slice.The default implementation delegates to
slice(String, long, long)and ignores theReadAdvice.- Throws:
IOException
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getFullSliceDescription
Subclasses call this to get the String for resourceDescription of a slice of thisIndexInput. -
randomAccessSlice
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
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prefetch
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 offsetlength- the number of bytes to prefetch- Throws:
IOException
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updateReadAdvice
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
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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.
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