类 org.apache.hadoop.mapreduce.Reducer
的使用

使用Reducer的程序包

程序包	说明
org.apache.hadoop.examples	Hadoop example code.
org.apache.hadoop.mapred	A software framework for easily writing applications which process vast amounts of data (multi-terabyte data-sets) parallelly on large clusters (thousands of nodes) built of commodity hardware in a reliable, fault-tolerant manner.
org.apache.hadoop.mapreduce
org.apache.hadoop.mapreduce.lib.fieldsel
org.apache.hadoop.mapreduce.lib.reduce

org.apache.hadoop.examples中Reducer的使用

org.apache.hadoop.examples中Reducer的子类

限定符和类型	类和说明
static class	SecondarySort.Reduce A reducer class that just emits the sum of the input values.
static class	WordCount.IntSumReducer

org.apache.hadoop.mapred中Reducer的使用

参数类型为Reducer的org.apache.hadoop.mapred中的方法

限定符和类型	方法和说明
protected static <INKEY,INVALUE,OUTKEY,OUTVALUE> Reducer.Context	Task.createReduceContext(Reducer<INKEY,INVALUE,OUTKEY,OUTVALUE> reducer, Configuration job, TaskAttemptID taskId, RawKeyValueIterator rIter, Counter inputKeyCounter, Counter inputValueCounter, RecordWriter<OUTKEY,OUTVALUE> output, OutputCommitter committer, StatusReporter reporter, RawComparator<INKEY> comparator, Class<INKEY> keyClass, Class<INVALUE> valueClass)

org.apache.hadoop.mapreduce中Reducer的使用

返回变量类型为Reducer的类型的org.apache.hadoop.mapreduce中的方法

限定符和类型	方法和说明
Class<? extends Reducer<?,?,?,?>>	JobContext.getCombinerClass() Get the combiner class for the job.
Class<? extends Reducer<?,?,?,?>>	JobContext.getReducerClass() Get the Reducer class for the job.

类型变量类型为Reducer的org.apache.hadoop.mapreduce中的方法参数

限定符和类型	方法和说明
void	Job.setCombinerClass(Class<? extends Reducer> cls) Set the combiner class for the job.
void	Job.setReducerClass(Class<? extends Reducer> cls) Set the Reducer for the job.

org.apache.hadoop.mapreduce.lib.fieldsel中Reducer的使用

org.apache.hadoop.mapreduce.lib.fieldsel中Reducer的子类

限定符和类型	类和说明
class	FieldSelectionReducer<K,V> This class implements a reducer class that can be used to perform field selections in a manner similar to unix cut.

org.apache.hadoop.mapreduce.lib.reduce中Reducer的使用

org.apache.hadoop.mapreduce.lib.reduce中Reducer的子类

限定符和类型	类和说明
class	IntSumReducer<Key>
class	LongSumReducer<KEY>