Package org.apache.lucene.store

Class DataInput

java.lang.Object

org.apache.lucene.store.DataInput

All Implemented Interfaces:

Cloneable

Direct Known Subclasses:

ByteArrayDataInput, ByteBuffersDataInput, ByteSliceReader, FST.BytesReader, IndexInput, InputStreamDataInput, PagedBytes.PagedBytesDataInput

public abstract class DataInput
extends Object
implements Cloneable

Abstract base class for performing read operations of Lucene's low-level data types.

DataInput 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 DataInput instance must be cloned before used in another thread. Subclasses must therefore implement clone(), returning a new DataInput which operates on the same underlying resource, but positioned independently.

Field Summary

Fields

Modifier and Type	Field	Description
private static final int	SKIP_BUFFER_SIZE
private byte[]	skipBuffer

Constructor Summary

Constructors

Constructor	Description
DataInput()

Method Summary

Modifier and Type	Method	Description
DataInput	clone()	Returns a clone of this stream.
abstract byte	readByte()	Reads and returns a single byte.
abstract void	readBytes(byte[] b, int offset, int len)	Reads a specified number of bytes into an array at the specified offset.
void	readBytes(byte[] b, int offset, int len, boolean useBuffer)	Reads a specified number of bytes into an array at the specified offset with control over whether the read should be buffered (callers who have their own buffer should pass in "false" for useBuffer).
int	readInt()	Reads four bytes and returns an int.
void	readLELongs(long[] dst, int offset, int length)	Read a specified number of longs with the little endian byte order.
long	readLong()	Reads eight bytes and returns a long.
Map<String,String>	readMapOfStrings()	Reads a Map<String,String> previously written with DataOutput.writeMapOfStrings(Map).
Set<String>	readSetOfStrings()	Reads a Set<String> previously written with DataOutput.writeSetOfStrings(Set).
short	readShort()	Reads two bytes and returns a short.
String	readString()	Reads a string.
int	readVInt()	Reads an int stored in variable-length format.
long	readVLong()	Reads a long stored in variable-length format.
private long	readVLong(boolean allowNegative)
int	readZInt()	Read a zig-zag-encoded variable-length integer.
long	readZLong()	Read a zig-zag-encoded variable-length integer.
void	skipBytes(long numBytes)	Skip over numBytes bytes.

Methods inherited from class java.lang.Object

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

Field Details

SKIP_BUFFER_SIZE

private static final int SKIP_BUFFER_SIZE

See Also:

• Constant Field Values

skipBuffer

private byte[] skipBuffer

Constructor Details

DataInput

public DataInput()

Method Details

readByte

public abstract byte readByte()
                       throws IOException

Reads and returns a single byte.

Throws:

IOException

See Also:

• DataOutput.writeByte(byte)

readBytes

public abstract void readBytes(byte[] b,
 int offset,
 int len)
                        throws IOException

Reads a specified number of bytes into an array at the specified offset.

Parameters:

b - the array to read bytes into

offset - the offset in the array to start storing bytes

len - the number of bytes to read

Throws:

IOException

See Also:

• DataOutput.writeBytes(byte[],int)

readBytes

public void readBytes(byte[] b,
 int offset,
 int len,
 boolean useBuffer)
               throws IOException

Reads a specified number of bytes into an array at the specified offset with control over whether the read should be buffered (callers who have their own buffer should pass in "false" for useBuffer). Currently only BufferedIndexInput respects this parameter.

Parameters:

b - the array to read bytes into

offset - the offset in the array to start storing bytes

len - the number of bytes to read

useBuffer - set to false if the caller will handle buffering.

Throws:

IOException

See Also:

• DataOutput.writeBytes(byte[],int)

readShort

public short readShort()
                throws IOException

Reads two bytes and returns a short.

Throws:

IOException

See Also:

• DataOutput.writeByte(byte)

readInt

public int readInt()
            throws IOException

Reads four bytes and returns an int.

Throws:

IOException

See Also:

• DataOutput.writeInt(int)

readVInt

public int readVInt()
             throws IOException

Reads an int stored in variable-length format. Reads between one and five bytes. Smaller values take fewer bytes. Negative numbers are supported, but should be avoided.

The format is described further in DataOutput.writeVInt(int).

Throws:

IOException

See Also:

• DataOutput.writeVInt(int)

readZInt

public int readZInt()
             throws IOException

Read a zig-zag-encoded variable-length integer.

Throws:

IOException

See Also:

• DataOutput.writeZInt(int)

readLong

public long readLong()
              throws IOException

Reads eight bytes and returns a long.

Throws:

IOException

See Also:

• DataOutput.writeLong(long)

readLELongs

public void readLELongs(long[] dst,
 int offset,
 int length)
                 throws IOException

Read a specified number of longs with the little endian byte order.

This method can be used to read longs whose bytes have been reversed at write time:

 for (long l : longs) {
   output.writeLong(Long.reverseBytes(l));
 }
 

Throws:

IOException

readVLong

public long readVLong()
               throws IOException

Reads a long stored in variable-length format. Reads between one and nine bytes. Smaller values take fewer bytes. Negative numbers are not supported.

The format is described further in DataOutput.writeVInt(int).

Throws:

IOException

See Also:

• DataOutput.writeVLong(long)

readVLong

private long readVLong(boolean allowNegative)
                throws IOException

Throws:

IOException

readZLong

public long readZLong()
               throws IOException

Read a zig-zag-encoded variable-length integer. Reads between one and ten bytes.

Throws:

IOException

See Also:

• DataOutput.writeZLong(long)

readString

public String readString()
                  throws IOException

Reads a string.

Throws:

IOException

See Also:

• DataOutput.writeString(String)

clone

public DataInput 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.

Overrides:

clone in class Object

readMapOfStrings

public Map<String,String> readMapOfStrings()
                                    throws IOException

Reads a Map<String,String> previously written with DataOutput.writeMapOfStrings(Map).

Returns:

An immutable map containing the written contents.

Throws:

IOException

readSetOfStrings

public Set<String> readSetOfStrings()
                             throws IOException

Reads a Set<String> previously written with DataOutput.writeSetOfStrings(Set).

Returns:

An immutable set containing the written contents.

Throws:

IOException

skipBytes

public void skipBytes(long numBytes)
               throws IOException

Skip over numBytes bytes. The contract on this method is that it should have the same behavior as reading the same number of bytes into a buffer and discarding its content. Negative values of numBytes are not supported.

Throws:

IOException