public abstract class DataJoinMapperBase extends JobBase
限定符和类型 | 字段和说明 |
---|---|
protected String |
inputFile |
protected Text |
inputTag |
protected JobConf |
job |
protected Reporter |
reporter |
构造器和说明 |
---|
DataJoinMapperBase() |
限定符和类型 | 方法和说明 |
---|---|
void |
close() |
void |
configure(JobConf job)
Initializes a new instance from a
JobConf . |
protected abstract Text |
generateGroupKey(TaggedMapOutput aRecord)
Generate a map output key.
|
protected abstract Text |
generateInputTag(String inputFile)
Determine the source tag based on the input file name.
|
protected abstract TaggedMapOutput |
generateTaggedMapOutput(Object value)
Generate a tagged map output value.
|
void |
map(Object key,
Object value,
OutputCollector output,
Reporter reporter)
Maps a single input key/value pair into an intermediate key/value pair.
|
void |
reduce(Object arg0,
Iterator arg1,
OutputCollector arg2,
Reporter arg3)
Reduces values for a given key.
|
addDoubleValue, addLongValue, getDoubleValue, getLongValue, getReport, report, setDoubleValue, setLongValue
protected String inputFile
protected JobConf job
protected Text inputTag
protected Reporter reporter
public void configure(JobConf job)
JobBase
JobConf
.configure
在接口中 JobConfigurable
configure
在类中 JobBase
job
- the configurationprotected abstract Text generateInputTag(String inputFile)
inputFile
- protected abstract TaggedMapOutput generateTaggedMapOutput(Object value)
value
- protected abstract Text generateGroupKey(TaggedMapOutput aRecord)
aRecord
- public void map(Object key, Object value, OutputCollector output, Reporter reporter) throws IOException
Mapper
Output pairs need not be of the same types as input pairs. A given
input pair may map to zero or many output pairs. Output pairs are
collected with calls to
OutputCollector.collect(Object,Object)
.
Applications can use the Reporter
provided to report progress
or just indicate that they are alive. In scenarios where the application
takes an insignificant amount of time to process individual key/value
pairs, this is crucial since the framework might assume that the task has
timed-out and kill that task. The other way of avoiding this is to set
mapred.task.timeout to a high-enough value (or even zero for no
time-outs).
key
- the input key.value
- the input value.output
- collects mapped keys and values.reporter
- facility to report progress.IOException
public void close() throws IOException
IOException
public void reduce(Object arg0, Iterator arg1, OutputCollector arg2, Reporter arg3) throws IOException
Reducer
The framework calls this method for each
<key, (list of values)>
pair in the grouped inputs.
Output values must be of the same type as input values. Input keys must
not be altered. The framework will reuse the key and value objects
that are passed into the reduce, therefore the application should clone
the objects they want to keep a copy of. In many cases, all values are
combined into zero or one value.
Output pairs are collected with calls to
OutputCollector.collect(Object,Object)
.
Applications can use the Reporter
provided to report progress
or just indicate that they are alive. In scenarios where the application
takes an insignificant amount of time to process individual key/value
pairs, this is crucial since the framework might assume that the task has
timed-out and kill that task. The other way of avoiding this is to set
mapred.task.timeout to a high-enough value (or even zero for no
time-outs).
arg0
- the key.arg1
- the list of values to reduce.arg2
- to collect keys and combined values.arg3
- facility to report progress.IOException
Copyright © 2009 The Apache Software Foundation