【liunx基础_6】MR代码

如何理解MapperLongWritable,Text,Text,IntWritable和ReducerText,IntWritable,Text,IntWritable

1.Mapper

importjava.io.IOException;

importorg.apache.hadoop.io.IntWritable;
importorg.apache.hadoop.io.LongWritable;
importorg.apache.hadoop.io.Text;
importorg.apache.hadoop.mapreduce.Mapper;

/**
*LongWritable偏移量long，表示该行在文件中的位置，而不是行号
*Textmap阶段的输入数据一行文本信息字符串类型String
*Textmap阶段的数据字符串类型String
*IntWritablemap阶段输出的value类型，对应java中的int型，表示行号
*/
publicclassWorkCountMapextendsMapper<LongWritable,Text,Text,IntWritable>{
/**
	*key输入的键
	*value输入的值
	*context上下文对象	
	*/
	@Override
    protectedvoidmap(LongWritablekey,Textvalue,Contextcontext)
    	throwsIOException,InterruptedException{
    	Stringline=value.toString();
    	String[]words=line.split("/t");//分词
    	for(Stringword:words{
    		TextwordText=newText(word);
    		IntWritableoutValue=newIntWritable();
    		//写出
    		context.write(wordText,outValue);
   		   }
 		  }
    	 }

2.Reduce
reduce阶段的输入 是mapper阶段的输出

importjava.io.IOException;
importorg.apache.hadoop.io.IntWritable;
importorg.apache.hadoop.io.Text;
importorg.apache.hadoop.mapreduce.Reducer;
/**
	*Text  数据类型：字符串类型String
	*IntWritable reduce阶段的输入类型int
	*Textreduce阶段的输出数据类型String类型
	*IntWritable输出词频个数Int型
	*/
	publicclassWorkCountReduceextendsReducer<Text,IntWritable,Text,IntWritable>{
		/**
			*key输入的键
			*value输入的值
			*context上下文对象,用于输出键值对
			*/			
			@Override
			protectedvoidreduce(Textkey,Iterable<IntWritable>value,
				Contextcontext)throwsIOException,InterruptedException{
					
					intsum=0;
					for(IntWritablenumber:value{
						sum+=number.get();
					}
					//单词   个数   hadoop  10
					context.write(key,newIntWritable(sum));
				}
			}