MapReduce之Reduce Join

一 介绍

Reduce Join其主要思想如下：
 在map阶段，map函数同时读取两个文件File1和File2，为了区分两种来源的key/value数据对，对每条数据打一个标签（tag）， 比如：tag=0表示来自文件File1，tag=2表示来自文件File2。即：map阶段的主要任务是对不同文件中的数据打标签。在reduce阶段，reduce函数获取key相同的来自File1和File2文件的value list， 然后对于同一个key，对File1和File2中的数据进行join（笛卡尔乘积)，即：reduce阶段进行实际的连接操作。

在这个例子中我们假设有两个数据文件如下：
存储客户信息的文件：customers.csv

1,stephaie leung,555-555-5555
2,edward kim,123-456-7890
3,jose madriz,281-330-8004
4,david storkk,408-55-0000

存储订单信息的文件：orders.csv

3,A,12.95,02-Jun-2008
1,B,88.25,20-May-2008
2,C,32.00,30-Nov-2007
3,D,25.02,22-Jan-2009

要求最终的输出结果为：

1,Stephanie Leung,555-555-5555,B,88.25,20-May-2008
2,Edward Kim,123-456-7890,C,32.00,30-Nov-2007
3,Jose Madriz,281-330-8004,A,12.95,02-Jun-2008
3,Jose Madriz,281-330-8004,D,25.02,22-Jan-2009

二 代码部分

自定义数据类型：用于对不同文件数据打标签

 1 package mapreduce.reducejoin;
 2 
 3 import java.io.DataInput;
 4 import java.io.DataOutput;
 5 import java.io.IOException;
 6 import org.apache.hadoop.io.Writable;
 7 
 8 public class DataJoinWritable implements Writable {
 9 
10     // mark ,customer / order
11     private String tag;
12 
13     // info
14     private String data;
15 
16     public DataJoinWritable() {
17 
18     }
19 
20     public DataJoinWritable(String tag, String data) {
21         this.set(tag, data);
22     }
23 
24     public void set(String tag, String data) {
25         this.setTag(tag);
26         this.setData(data);
27     }
28 
29     public String getTag() {
30         return tag;
31     }
32 
33     public void setTag(String tag) {
34         this.tag = tag;
35     }
36 
37     public String getData() {
38         return data;
39     }
40 
41     public void setData(String data) {
42         this.data = data;
43     }
44 
45     public void write(DataOutput out) throws IOException {
46         out.writeUTF(this.getTag());
47         out.writeUTF(this.getData());
48     }
49 
50     public void readFields(DataInput in) throws IOException {
51         this.setTag(in.readUTF());
52         this.setData(in.readUTF());
53     }
54 
55     @Override
56     public int hashCode() {
57         final int prime = 31;
58         int result = 1;
59         result = prime * result + ((data == null) ? 0 : data.hashCode());
60         result = prime * result + ((tag == null) ? 0 : tag.hashCode());
61         return result;
62     }
63 
64     @Override
65     public boolean equals(Object obj) {
66         if (this == obj)
67             return true;
68         if (obj == null)
69             return false;
70         if (getClass() != obj.getClass())
71             return false;
72         DataJoinWritable other = (DataJoinWritable) obj;
73         if (data == null) {
74             if (other.data != null)
75                 return false;
76         } else if (!data.equals(other.data))
77             return false;
78         if (tag == null) {
79             if (other.tag != null)
80                 return false;
81         } else if (!tag.equals(other.tag))
82             return false;
83         return true;
84     }
85 
86     @Override
87     public String toString() {
88         return tag + "," + data;
89     }
90 }

MapReduce代码部分

  1 package mapreduce.reducejoin;
  2 
  3 import java.io.IOException;
  4 import java.util.ArrayList;
  5 import java.util.List;
  6 import org.apache.hadoop.conf.Configuration;
  7 import org.apache.hadoop.conf.Configured;
  8 import org.apache.hadoop.fs.Path;
  9 import org.apache.hadoop.io.LongWritable;
 10 import org.apache.hadoop.io.NullWritable;
 11 import org.apache.hadoop.io.Text;
 12 import org.apache.hadoop.mapreduce.Job;
 13 import org.apache.hadoop.mapreduce.Mapper;
 14 import org.apache.hadoop.mapreduce.Reducer;
 15 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
 16 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
 17 import org.apache.hadoop.util.Tool;
 18 import org.apache.hadoop.util.ToolRunner;
 19 
 20 public class DataJoinMapReduce extends Configured implements Tool {
 21 
 22     // step 1: Mapper
 23     public static class DataJoinMapper extends
 24             Mapper<LongWritable, Text, LongWritable, DataJoinWritable> {
 25 
 26         // map output key
 27         private LongWritable mapOutputKey = new LongWritable();
 28 
 29         // map output value
 30         private DataJoinWritable mapOutputValue = new DataJoinWritable();
 31 
 32         @Override
 33         public void setup(Context context) throws IOException,
 34                 InterruptedException {
 35         }
 36 
 37         @Override
 38         public void map(LongWritable key, Text value, Context context)
 39                 throws IOException, InterruptedException {
 40 
 41             // line value
 42             String lineValue = value.toString();
 43 
 44             // split
 45             String[] vals = lineValue.split(",");
 46 
 47             int length = vals.length;
 48 
 49             if ((3 != length) && (4 != length)) {
 50                 return;
 51             }
 52 
 53             // get cid
 54             Long cid = Long.valueOf(vals[0]);
 55 
 56             // get name
 57             String name = vals[1];
 58 
 59             // set customer
 60             if (3 == length) {
 61                 String phone = vals[2];
 62 
 63                 // set
 64                 mapOutputKey.set(cid);
 65                 mapOutputValue.set("customer", name + "," + phone);
 66             }
 67 
 68             // set order
 69             if (4 == length) {
 70                 String price = vals[2];
 71                 String date = vals[3];
 72 
 73                 // set
 74                 mapOutputKey.set(cid);
 75                 mapOutputValue.set("order", name + "," + price + "," + date);
 76             }
 77 
 78             // output
 79             context.write(mapOutputKey, mapOutputValue);
 80 
 81         }
 82 
 83         @Override
 84         public void cleanup(Context context) throws IOException,
 85                 InterruptedException {
 86         }
 87     }
 88 
 89     // step 2: Reducer
 90     public static class DataJoinReducer extends
 91             Reducer<LongWritable, DataJoinWritable, NullWritable, Text> {
 92 
 93         private Text outputValue = new Text();
 94 
 95         @Override
 96         protected void setup(Context context) throws IOException,
 97                 InterruptedException {
 98         }
 99 
100         @Override
101         protected void reduce(LongWritable key,
102                 Iterable<DataJoinWritable> values, Context context)
103                 throws IOException, InterruptedException {
104             String customerInfo = null;
105             List<String> orderList = new ArrayList<String>();
106 
107             for (DataJoinWritable value : values) {
108                 if ("customer".equals(value.getTag())) {
109                     customerInfo = value.getData();
110                 } else if ("order".equals(value.getTag())) {
111                     orderList.add(value.getData());
112                 }
113             }
114 
115             // output
116             for (String order : orderList) {
117 
118                 // ser outout value
119                 outputValue.set(key.get() + "," + customerInfo + "," + order);
120 
121                 // output
122                 context.write(NullWritable.get(), outputValue);
123             }
124         }
125 
126         @Override
127         protected void cleanup(Context context) throws IOException,
128                 InterruptedException {
129         }
130     }
131 
132     /**
133      * Execute the command with the given arguments.
134      * 
135      * @param args
136      *            command specific arguments.
137      * @return exit code.
138      * @throws Exception
139      */
140 
141     // step 3: Driver
142     public int run(String[] args) throws Exception {
143 
144         Configuration configuration = this.getConf();
145         
146         // set job
147         Job job = Job.getInstance(configuration, this.getClass().getSimpleName());
148         job.setJarByClass(DataJoinMapReduce.class);
149         
150         // input
151         Path inpath = new Path(args[0]);
152         FileInputFormat.addInputPath(job, inpath);
153 
154         // output
155         Path outPath = new Path(args[1]);
156         FileOutputFormat.setOutputPath(job, outPath);
157 
158         // Mapper
159         job.setMapperClass(DataJoinMapper.class);
160         job.setMapOutputKeyClass(LongWritable.class);
161         job.setMapOutputValueClass(DataJoinWritable.class);
162 
163         // Reducer
164         job.setReducerClass(DataJoinReducer.class);
165         job.setOutputKeyClass(NullWritable.class);
166         job.setOutputValueClass(Text.class);
167 
168         // submit job -> YARN
169         boolean isSuccess = job.waitForCompletion(true);
170         return isSuccess ? 0 : 1;
171 
172     }
173 
174     public static void main(String[] args) throws Exception {
175 
176         Configuration configuration = new Configuration();
177 
178         args = new String[] {
179                 "hdfs://beifeng01:8020/user/beifeng01/mapreduce/input/reducejoin",
180                 "hdfs://beifeng01:8020/user/beifeng01/mapreduce/output" };
181 
182         // run job
183         int status = ToolRunner.run(configuration, new DataJoinMapReduce(),
184                 args);
185 
186         // exit program
187         System.exit(status);
188     }
189 }

执行代码后查询结果

[hadoop@beifeng01 hadoop-2.5.0-cdh5.3.6]$ bin/hdfs dfs -text /user/beifeng01/mapreduce/output/p*
1,stephaie leung,555-555-5555,B,88.25,20-May-2008
2,edward kim,123-456-7890,C,32.00,30-Nov-2007
3,jose madriz,281-330-8004,D,25.02,22-Jan-2009
3,jose madriz,281-330-8004,A,12.95,02-Jun-2008

 

posted on 2018-12-15 22:17  PerfectData  阅读(589)  评论(0)  编辑  收藏  举报

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