定義 Reducer

package cn.learn.mapreduce_reduce_join;import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Reducer;import java.io.IOException;public class ReduceJoinReducer extends Reducer<Text,Text,Text,Text> {@Overrideprotected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {String first = "";String second = "";for (Text value : values) {if(value.toString().startsWith("p")){first = value.toString();}else{second = value.toString();}}if(first.equals("")){context.write(key, new Text("NULL"+"\t"+second));}else{context.write(key, new Text(first+"\t"+second));}} }

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