写Hadoop分析数据的代码
时间: 2024-05-10 15:16:58 浏览: 12
以下是一个使用Hadoop MapReduce分析数据的例子:
假设有一个文本文件,其中包含一些单词,我们想要计算每个单词出现的次数。
1. 首先,我们需要编写一个Mapper类来处理每行文本:
```
public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
@Override
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
String line = value.toString();
StringTokenizer tokenizer = new StringTokenizer(line);
while (tokenizer.hasMoreTokens()) {
word.set(tokenizer.nextToken());
context.write(word, one);
}
}
}
```
2. 接下来,我们需要编写一个Reducer类来聚合Mapper的输出:
```
public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
private IntWritable result = new IntWritable();
@Override
public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : values) {
sum += val.get();
}
result.set(sum);
context.write(key, result);
}
}
```
3. 最后,我们需要编写一个主类来配置和运行MapReduce作业:
```
public class WordCount {
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "word count");
job.setJarByClass(WordCount.class);
job.setMapperClass(WordCountMapper.class);
job.setCombinerClass(WordCountReducer.class);
job.setReducerClass(WordCountReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
```
这个例子中,我们使用了Hadoop MapReduce来处理一个简单的单词计数问题。我们首先编写了一个Mapper类来处理每行文本,将每个单词映射到一个计数为1的键值对。然后我们编写了一个Reducer类来聚合Mapper的输出,统计每个单词出现的总次数。最后,我们编写了一个主类来配置和运行MapReduce作业,指定输入和输出文件路径,并等待作业完成。
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