实验内容
现有某电商网站用户对商品的收藏数据，记录了用户收藏的商品id以及收藏日期，名为buyer_favorite1。
buyer_favorite1包含：买家id，商品id，收藏日期这三个字段，数据以“\t”分割，样本数据及格式如下：
- 买家id 商品id 收藏日期
- 10181 1000481 2010-04-04 16:54:31
- 20001 1001597 2010-04-07 15:07:52
- 20001 1001560 2010-04-07 15:08:27
- 20042 1001368 2010-04-08 08:20:30
- 20067 1002061 2010-04-08 16:45:33
- 20056 1003289 2010-04-12 10:50:55
- 20056 1003290 2010-04-12 11:57:35
- 20056 1003292 2010-04-12 12:05:29
- 20054 1002420 2010-04-14 15:24:12
- 20055 1001679 2010-04-14 19:46:04
- 20054 1010675 2010-04-14 15:23:53
- 20054 1002429 2010-04-14 17:52:45
- 20076 1002427 2010-04-14 19:35:39
- 20054 1003326 2010-04-20 12:54:44
- 20056 1002420 2010-04-15 11:24:49
- 20064 1002422 2010-04-15 11:35:54
- 20056 1003066 2010-04-15 11:43:01
- 20056 1003055 2010-04-15 11:43:06
- 20056 1010183 2010-04-15 11:45:24
- 20056 1002422 2010-04-15 11:45:49
- 20056 1003100 2010-04-15 11:45:54
- 20056 1003094 2010-04-15 11:45:57
- 20056 1003064 2010-04-15 11:46:04
- 20056 1010178 2010-04-15 16:15:20
- 20076 1003101 2010-04-15 16:37:27
- 20076 1003103 2010-04-15 16:37:05
- 20076 1003100 2010-04-15 16:37:18
- 20076 1003066 2010-04-15 16:37:31
- 20054 1003103 2010-04-15 16:40:14
- 20054 1003100 2010-04-15 16:40:16
要求编写MapReduce程序，统计每个买家收藏商品数量。
统计结果数据如下：
- 买家id 商品数量
- 10181 1
- 20001 2
- 20042 1
- 20054 6
- 20055 1
- 20056 12
- 20064 1
- 20067 1
- 20076 5
源代码：package mapreduce;
import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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 WordCount {
public static void main(String[] args) throws IOException,ClassNotFoundException,InterruptedException {
Job job = Job.getInstance();
job.setJobName("WordCount");
job.setJarByClass(WordCount.class);
job.setMapperClass(doMapper.class);
job.setReducerClass(doReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
Path in = new Path("hdfs://localhost:9000/mymapreduce1/in/buyer_favoritel");
Path out = new Path("hdfs://localhost:9000/mymapreduce1/out");
FileInputFormat.addInputPath(job,in);
FileOutputFormat.setOutputPath(job,out);
System.exit(job.waitForCompletion(true)?0:1);
}
public static class doMapper extends Mapper<Object,Text,Text,IntWritable>{
public static final IntWritable one = new IntWritable(1);
public static Text word = new Text();
@Override
protected void map(Object key, Text value, Context context)
throws IOException,InterruptedException {
StringTokenizer tokenizer = new StringTokenizer(value.toString()," ");
word.set(tokenizer.nextToken());
context.write(word,one);
}
}
public static class doReducer extends Reducer<Text,IntWritable,Text,IntWritable>{
private IntWritable result = new IntWritable();
@Override
protected void reduce(Text key,Iterable<IntWritable> values,Context context)
throws IOException,InterruptedException{
int sum = 0;
for (IntWritable value : values){
sum += value.get();
}
result.set(sum);
context.write(key,result);
}
}
}
结果截图：
实验感想：
这次实验遇到了很多问题：
- 虚拟机因为版本问题从主机向虚拟机复制文件是死机了。
- VMware虚拟机复制粘贴功能无法使用。解决办法：先确定有没有安装VMware Tools，如果没有安装VMware Tools先安装VMware Tools。安装VMware Tools完成后点击虚拟机选择设置，然后在选项中的客户机隔离把启用复制粘贴勾选上，还有就是共享文件夹改为启用。选上以后一定要重启虚拟机！！！这样就可以从主机到虚拟机上的复制粘贴了。
3. Hadoop运行错误 - Output directory hdfs://master:9000/output already exists
这个就是因为hdfs的output目录已经存在。解决方案：删除相应文件或文件夹：
/usr/loca/hadoop/bin/hadoop fs -rm -r output
4 . 
这个问题很恶心，你检查shell语句是否打错了是检查不出来的，这个错误是因为/mymapreduce1/in前面没有空格，没有空格的话他会认为后面的也是文件夹或目录