org.apache.hadoop.mapred

接口 RecordReader<K,V>

所有已知子接口:

ComposableRecordReader<K,V>

所有已知实现类:

CombineFileRecordReader, DBInputFormat.DBRecordReader, InnerJoinRecordReader, JoinRecordReader, KeyValueLineRecordReader, LineDocRecordReader, LineRecordReader, MultiFileWordCount.MultiFileLineRecordReader, MultiFilterRecordReader, OuterJoinRecordReader, OverrideRecordReader, SequenceFileAsBinaryInputFormat.SequenceFileAsBinaryRecordReader, SequenceFileAsTextRecordReader, SequenceFileRecordReader, StreamBaseRecordReader, StreamXmlRecordReader, WrappedRecordReader

public interface RecordReader<K,V>

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 & Reducer tasks for processing. It thus assumes the responsibility of processing record boundaries and presenting the tasks with keys and values.

另请参阅:

InputSplit, InputFormat

方法概要

方法

限定符和类型	方法和说明
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.

方法详细资料

next

boolean next(K key,
           V value)
             throws IOException

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

参数:

key - the key to read data into

value - the value to read data into

返回:

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

抛出:

IOException

createKey

K createKey()

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

返回:

a new key object.

createValue

V createValue()

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

返回:

a new value object.

getPos

long getPos()
            throws IOException

Returns the current position in the input.

返回:

the current position in the input.

抛出:

IOException

close

void close()
           throws IOException

Close this InputSplit to future operations.

抛出:

IOException

getProgress

float getProgress()
                  throws IOException

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

返回:

progress from 0.0 to 1.0.

抛出:

IOException