hadoop统计以a和b字母开头的单词的个数代码

下面是一个简单的Hadoop MapReduce代码，用于统计以a和b字母开头的单词的个数：

Mapper类：

public class ABWordCountMapper 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()) {
            String nextToken = tokenizer.nextToken();
            if (nextToken.startsWith("a") || nextToken.startsWith("b")) {
                word.set(nextToken);
                context.write(word, one);
            }
        }
    }
}

Reducer类：

public class ABWordCountReducer 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);
    }
}

Driver类：

public class ABWordCountDriver {
    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "AB word count");
        job.setJarByClass(ABWordCountDriver.class);
        job.setMapperClass(ABWordCountMapper.class);
        job.setCombinerClass(ABWordCountReducer.class);
        job.setReducerClass(ABWordCountReducer.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);
    }
}

在运行MapReduce作业之前，请确保已经安装并配置好了Hadoop，并且已经将输入文件上传到HDFS中。使用以下命令来提交MapReduce作业：

hadoop jar ABWordCount.jar ABWordCountDriver input output

其中，ABWordCount.jar是包含所有类文件的JAR文件，input是输入文件的路径，output是输出文件的路径。