org.apache.hadoop.mapred

Interface RecordReader<K,V>

All Superinterfaces:

AutoCloseable, Closeable

All Known Subinterfaces:

ComposableRecordReader<K,V>

All Known Implementing Classes:

CombineFileRecordReader, CombineFileRecordReaderWrapper, InnerJoinRecordReader, JoinRecordReader, KeyValueLineRecordReader, MultiFilterRecordReader, OuterJoinRecordReader, OverrideRecordReader, SequenceFileAsTextRecordReader, SequenceFileRecordReader, WrappedRecordReader

@InterfaceAudience.Public
 @InterfaceStability.Stable
public interface RecordReader<K,V>
extends Closeable

RecordReader reads <key, value> pairs from an InputSplit.

RecordReader, typically, converts the byte-oriented view of the input, provided by the InputSplit, and presents a record-oriented view for the Mapper and Reducer tasks for processing. It thus assumes the responsibility of processing record boundaries and presenting the tasks with keys and values.

See Also:

InputSplit, InputFormat

Method Summary

Modifier and Type	Method and Description
void	close() Close this InputSplit to future operations.
K	createKey() Create an object of the appropriate type to be used as a key.
V	createValue() Create an object of the appropriate type to be used as a value.
long	getPos() Returns the current position in the input.
float	getProgress() How much of the input has the RecordReader consumed i.e.
boolean	next(K key, V value) Reads the next key/value pair from the input for processing.

Method Detail

next

boolean next(K key,
             V value)
      throws IOException

Reads the next key/value pair from the input for processing.

Parameters:

key - the key to read data into

value - the value to read data into

Returns:

true iff a key/value was read, false if at EOF

Throws:

IOException

createKey

K createKey()

Create an object of the appropriate type to be used as a key.

Returns:

a new key object.

createValue

V createValue()

Create an object of the appropriate type to be used as a value.

Returns:

a new value object.

getPos

long getPos()
     throws IOException

Returns the current position in the input.

Returns:

the current position in the input.

Throws:

IOException

close

void close()
    throws IOException

Close this InputSplit to future operations.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException

getProgress

float getProgress()
           throws IOException

How much of the input has the RecordReader consumed i.e. has been processed by?

Returns:

progress from 0.0 to 1.0.

Throws:

IOException