输入格式：
     A　　1　　B,C,D
　　　B　　1　　C,D
map:
　　  B　　A　　1/3
　  　C　　A　　1/3
　  　D　　A　　1/3
　  　A　　|B,C,D
　  　C　　B　　1/2
　  　D　　B　　1/2
　  　B　　|C,D
reduce:
　　　B　　(1-0.85)+0.85*1/3　　C,D
  
　　　C　　(1-0.85)+0.85*5/6　　

     D　　(1-0.85)+0.85*5/6
     A    (1-0.85)+0.85*1　　B,C,D


import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;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.output.FileOutputFormat;public class PageRankIter {  private static final double damping = 0.85;  public static class PRIterMapper extends      Mapper<LongWritable, Text, Text, Text> {    public void map(LongWritable key, Text value, Context context)        throws IOException, InterruptedException {      String line = value.toString();      String[] tuple = line.split("\t");      String pageKey = tuple[0];      double pr = Double.parseDouble(tuple[1]);      if (tuple.length > 2) {        String[] linkPages = tuple[2].split(",");        for (String linkPage : linkPages) {          String prValue =              pageKey + "\t" + String.valueOf(pr / linkPages.length);          context.write(new Text(linkPage), new Text(prValue));        }        context.write(new Text(pageKey), new Text("|" + tuple[2]));      }    }  }  public static class PRIterReducer extends Reducer<Text, Text, Text, Text> {    public void reduce(Text key, Iterable<Text> values, Context context)        throws IOException, InterruptedException {      String links = "";      double pagerank = 0;      for (Text value : values) {        String tmp = value.toString();        if (tmp.startsWith("|")) {          links = "\t" + tmp.substring(tmp.indexOf("|") + 1);// index从0开始          continue;        }        String[] tuple = tmp.split("\t");        if (tuple.length > 1)          pagerank += Double.parseDouble(tuple[1]);      }      pagerank = (double) (1 - damping) + damping * pagerank; // PageRank的计算迭代公式      context.write(new Text(key), new Text(String.valueOf(pagerank) + links));    }  }  public static void main(String[] args) throws Exception {    Configuration conf = new Configuration();    Job job2 = new Job(conf, "PageRankIter");    job2.setJarByClass(PageRankIter.class);    job2.setOutputKeyClass(Text.class);    job2.setOutputValueClass(Text.class);    job2.setMapperClass(PRIterMapper.class);    job2.setReducerClass(PRIterReducer.class);    FileInputFormat.addInputPath(job2, new Path(args[0]));    FileOutputFormat.setOutputPath(job2, new Path(args[1]));    job2.waitForCompletion(true);  }}

输入为上述的输出
输入格式为：
    A　　pr
    B　　pr
    ...

import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.FloatWritable;import org.apache.hadoop.io.WritableComparable;import org.apache.hadoop.io.WritableComparator;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;public class PageRankViewer {  public static class PageRankViewerMapper extends      Mapper<LongWritable, Text, FloatWritable, Text> {    private Text outPage = new Text();    private FloatWritable outPr = new FloatWritable();    public void map(LongWritable key, Text value, Context context)        throws IOException, InterruptedException {      String[] line = value.toString().split("\t");      String page = line[0];      float pr = Float.parseFloat(line[1]);      outPage.set(page);      outPr.set(pr);      context.write(outPr, outPage);    }  }  /**重载key的比较函数，使其经过shuffle和sort后反序（从大到小）输出**/  public static class DescFloatComparator extends FloatWritable.Comparator {    // @Override    public float compare(WritableComparator a,        WritableComparable<FloatWritable> b) {      return -super.compare(a, b);    }    public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) {      return -super.compare(b1, s1, l1, b2, s2, l2);    }  }  public static void main(String[] args) throws Exception {      Configuration conf = new Configuration();      Job job3 = new Job(conf, "PageRankViewer");      job3.setJarByClass(PageRankViewer.class);      job3.setOutputKeyClass(FloatWritable.class);      job3.setSortComparatorClass(DescFloatComparator.class);      job3.setOutputValueClass(Text.class);      job3.setMapperClass(PageRankViewerMapper.class);      FileInputFormat.addInputPath(job3, new Path(args[0]));      FileOutputFormat.setOutputPath(job3, new Path(args[1]));      job3.waitForCompletion(true);  }}