使用hadoop mapreduce分析mongodb数据：（2）

> db.stackout.find({})
{ "_id" : "world", "data" : [  {  "url_2" : 2 },  {  "url_3" : 1 },  {  "url_4" : 1 } ], "index" : 0, "maxindex" : 3 }
{ "_id" : "good", "data" : [  {  "url_1" : 2 },  {  "url_2" : 1 },  {  "url_3" : 2 } ], "index" : 0, "maxindex" : 3 }
{ "_id" : "day", "data" : [  {  "url_1" : 1 } ], "index" : 0, "maxindex" : 1 }
{ "_id" : "hello", "data" : [  {  "url_2" : 1 },  {  "url_3" : 2 },  {  "url_4" : 2 } ], "index" : 0, "maxindex" : 3 }

我们需要统计每个单词在每个网页中分别出现的次数，从结果可知，单词world在每个url出现的次数

 1 import java.util.*; 
 2 import java.io.*;
 3 
 4 import org.bson.*;
 5 
 6 import com.mongodb.hadoop.MongoInputFormat;
 7 import com.mongodb.hadoop.MongoOutputFormat;
 8 import com.mongodb.hadoop.io.BSONWritable;
 9 
10 import org.apache.hadoop.conf.Configuration;
11 import org.apache.hadoop.io.*;
12 import org.apache.hadoop.mapreduce.*;
13 
14 
15 public class WordCount {
16 
17     public static class TokenizerMapper extends Mapper<Object, BSONObject, Text, BSONWritable> {
18         //private final static 
19         private Text word = new Text();
20 
21         public void map(Object key, BSONObject value, Context context ) 
22                 throws IOException, InterruptedException {
23             String url = value.get("url").toString();
24             StringTokenizer itr = new StringTokenizer(value.get("summary").toString().
25                     replaceAll("\\p{Punct}|\\d","").replaceAll("\r\n", " ").replace("\r", " ").
26                     replace("\n", " ").toLowerCase());
27             while (itr.hasMoreTokens()) {
28                 word.set(itr.nextToken());
29                 BasicBSONObject urlCounts = new BasicBSONObject();
30                 urlCounts.put(url, 1);
31                 context.write(word, new BSONWritable(urlCounts));
32             }
33         }
34     }
35 
36     public static class IntSumReducer extends Reducer<Text, BSONWritable, Text, BSONWritable> {
37         //private BasicBSONObject result = new BasicBSONObject();
38         
39         public void reduce(Text key, Iterable<BSONWritable> values, Context context)
40             throws IOException, InterruptedException {
41             HashMap<String, Integer> mymap = new HashMap<String, Integer>();
42             BasicBSONObject result = new BasicBSONObject();
43             BasicBSONObject urlcount = new BasicBSONObject();
44             for (BSONWritable val : values) {
45                 @SuppressWarnings("unchecked")
46                 BSONObject temp2 = val.getDoc();
47                 @SuppressWarnings("unchecked")
48                 HashMap<String, Integer> temp = (HashMap<String, Integer>) val.getDoc().toMap();
49                 for (Map.Entry<String, Integer> entry :  temp.entrySet()) {
50                     if (mymap.containsKey(entry.getKey())) {
51                         mymap.put(entry.getKey(), entry.getValue()+1);
52                     }
53                     else {
54                         mymap.put(entry.getKey(), 1);
55                     }
56                 }
57             }
58             result.putAll(mymap);
59             context.write(key, new BSONWritable(result));
60         }
61     }
62 
63     public static void main(String[] args) throws Exception {
64         Configuration conf = new Configuration();
65         conf.set( "mongo.input.uri" , "mongodb://localhost/stackoverflow.stackin" );
66         conf.set( "mongo.output.uri" , "mongodb://localhost/stackoverflow.stackout" );
67         @SuppressWarnings("deprecation")
68         Job job = new Job(conf, "word count");
69         job.setJarByClass(WordCount.class);
70         job.setMapperClass(TokenizerMapper.class);
71         //job.setCombinerClass(IntSumReducer.class);
72         job.setReducerClass(IntSumReducer.class);
73         job.setMapOutputKeyClass(Text.class);
74         job.setMapOutputValueClass(BSONWritable.class);
75         job.setOutputKeyClass(Text.class);
76         job.setOutputValueClass(BSONWritable.class);
77         job.setInputFormatClass( MongoInputFormat.class );
78         job.setOutputFormatClass( MongoOutputFormat.class );
79         System.exit(job.waitForCompletion(true) ? 0 : 1);
80     }
81 }

设计的思路是，在map部分得到一个word以及键为url值为1的Bson对象，然后写入content中。对应的，在reduce部分对传入的值进行统计。