org.apache.hadoop.mapreduce.lib.fieldsel

类 FieldSelectionMapper<K,V>

java.lang.Object

org.apache.hadoop.mapreduce.Mapper<K,V,Text,Text>

org.apache.hadoop.mapreduce.lib.fieldsel.FieldSelectionMapper<K,V>

@InterfaceAudience.Public
@InterfaceStability.Stable
public class FieldSelectionMapper<K,V>
extends Mapper<K,V,Text,Text>

This class implements a mapper class that can be used to perform field selections in a manner similar to unix cut. The input data is treated as fields separated by a user specified separator (the default value is "\t"). The user can specify a list of fields that form the map output keys, and a list of fields that form the map output values. If the inputformat is TextInputFormat, the mapper will ignore the key to the map function. and the fields are from the value only. Otherwise, the fields are the union of those from the key and those from the value. The field separator is under attribute "mapreduce.fieldsel.data.field.separator" The map output field list spec is under attribute "mapreduce.fieldsel.map.output.key.value.fields.spec". The value is expected to be like "keyFieldsSpec:valueFieldsSpec" key/valueFieldsSpec are comma (,) separated field spec: fieldSpec,fieldSpec,fieldSpec ... Each field spec can be a simple number (e.g. 5) specifying a specific field, or a range (like 2-5) to specify a range of fields, or an open range (like 3-) specifying all the fields starting from field 3. The open range field spec applies value fields only. They have no effect on the key fields. Here is an example: "4,3,0,1:6,5,1-3,7-". It specifies to use fields 4,3,0 and 1 for keys, and use fields 6,5,1,2,3,7 and above for values.

嵌套类概要

从类继承的嵌套类/接口 org.apache.hadoop.mapreduce.Mapper

Mapper.Context

字段概要

字段

限定符和类型	字段和说明
static org.apache.commons.logging.Log	LOG

构造器概要

构造器

构造器和说明
FieldSelectionMapper()

方法概要

方法

限定符和类型	方法和说明
void	map(K key, V val, Mapper.Context context) The identify function.
void	setup(Mapper.Context context) Called once at the beginning of the task.

从类继承的方法 org.apache.hadoop.mapreduce.Mapper

cleanup, run

从类继承的方法 java.lang.Object

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

字段详细资料

LOG

public static final org.apache.commons.logging.Log LOG

构造器详细资料

FieldSelectionMapper

public FieldSelectionMapper()

方法详细资料

setup

public void setup(Mapper.Context context)
           throws IOException,
                  InterruptedException

从类复制的说明: Mapper

Called once at the beginning of the task.

覆盖:

setup 在类中 Mapper<K,V,Text,Text>

抛出:

IOException

InterruptedException

map

public void map(K key,
       V val,
       Mapper.Context context)
         throws IOException,
                InterruptedException

The identify function. Input key/value pair is written directly to output.

覆盖:

map 在类中 Mapper<K,V,Text,Text>

抛出:

IOException

InterruptedException