mapreduce (三) MapReduce实现倒排索引(二)

hadoop api
http://hadoop.apache.org/docs/r1.0.4/api/org/apache/hadoop/mapreduce/Reducer.html

改变一下需求：要求“文档词频列表”是经过排序的，即 出现次数高的再前
 
思路：
 
代码：

package proj;
 
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
 
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.partition.HashPartitioner;
import org.apache.hadoop.util.GenericOptionsParser;
 
public class InvertedIndexSortByFreq {
 
    // 将词分为<word:num,docid>
    public static class InvertedIndexMapper extends
            Mapper<Object, Text, Text, Text> {
 
        private Text keyInfo = new Text();
        private Text valInfo = new Text();
        private FileSplit split;
 
        public void map(Object key, Text value, Context context)
                throws IOException, InterruptedException {
            String[] tokens = value.toString().split(" ");
            split = (FileSplit) context.getInputSplit();
            String docid = split.getPath().getName();
            Map<String, Integer> map = new HashMap<String, Integer>();
            for (String token : tokens) {
                if (map.containsKey(token)) {
                    Integer newInt = new Integer(map.get(token) + 1);
                    map.put(token, newInt);
                } else {
                    map.put(token, 1);
                }
            }
            for (String k : map.keySet()) {
                Integer num = map.get(k);
                keyInfo.set(k + ":" + num);
                valInfo.set(docid);
                context.write(keyInfo, valInfo);
            }
        }
    }
 
    public static class InvertedIndexPartioner extends
            HashPartitioner<Text, Text> {
 
        private Text term = new Text();
 
        public int getPartition(Text key, Text value, int numReduceTasks) {
            term.set(key.toString().split(":")[0] + ":" + value);
            return super.getPartition(term, value, numReduceTasks);
        }
    }
 
    // 组合成倒排索引文档
    public static class InvertedIndexReducer extends
            Reducer<Text, Text, Text, Text> {
        private Text keyInfo = new Text();
 
        private Text valInfo = new Text();
 
        private String tPrev = null;
 
        private StringBuffer buff = new StringBuffer();
 
        public void reduce(Text key, Iterable<Text> values, Context context)
                throws IOException, InterruptedException {
 
            String[] tokens = key.toString().split(":");
            String current = tokens[0];
 
            if (tPrev == null) {
                tPrev = current;
                for (Text val : values) {
                    buff.append(tokens[1] + ":" + val.toString() + ";");
                }
            }
 
            if(tPrev.equals(current)){
                for (Text val : values) {
                    buff.append(tokens[1] + ":" + val.toString() + ";");
                }
            }else{
                keyInfo.set(tPrev);
                valInfo.set(buff.toString());
                context.write(keyInfo,valInfo);
                tPrev = current;
                buff = new StringBuffer();
                for (Text val : values) {
                    buff.append(tokens[1] + ":" + val.toString() + ";");
                }
            }
        }
 
        public void cleanup(Context context) throws IOException, InterruptedException{
            keyInfo.set(tPrev);
            valInfo.set(buff.toString());
            context.write(keyInfo,valInfo);
            super.cleanup(context);
        }
 
    }
 
    public static void main(String[] args) throws IOException,
            ClassNotFoundException, InterruptedException {
        Configuration conf = new Configuration();
        String[] otherArgs = new GenericOptionsParser(conf, args)
                .getRemainingArgs();
        Job job = new Job(conf, "InvertedIndex");
        job.setJarByClass(InvertedIndex.class);
        job.setMapperClass(InvertedIndexMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(Text.class);
        job.setPartitionerClass(InvertedIndexPartioner.class);
        job.setReducerClass(InvertedIndexReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
 
}