注：测试数据在最后

写一个map-reduce，输出结果和下面的Hive查询语句相同

1. select * from customers where country="USA"

public class OutMapper extends Mapper<LongWritable, Text, LongWritable, Text>{
    public void map(LongWritable key, Text line, Context context){
        String[] info = line.toString().split(",");
        if("USA".equals(info[3])){
            try {
                context.write(key, line);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

public class OutReducer extends Reducer<LongWritable, Text, Text, NullWritable>{

    public void reduce(Text line,Iterable<Text> value, Context context){
        try {
            context.write(line, NullWritable.get());
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
}

public class OutRunner extends Configured implements Tool {

    public static void main(String[] args) {
        try {
            System.exit(ToolRunner.run(new OutRunner(), args));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public int run(String[] args) throws Exception {
        Job job = Job.getInstance(getConf(), "HQL");
        job.setJarByClass(getClass());

        FileInputFormat.addInputPath(job, new Path(args[0]));
        job.setInputFormatClass(TextInputFormat.class);

        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        job.setOutputFormatClass(TextOutputFormat.class);

        job.setMapperClass(OutMapper.class);
        job.setMapOutputKeyClass(LongWritable.class);
        job.setMapOutputValueClass(Text.class);
        job.setReducerClass(OutReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(NullWritable.class);

        return job.waitForCompletion(true) ? 0 : 1;
    }
}

2. select country, count(country) from customers group by country

public class OutMapper extends Mapper<LongWritable, Text, Text, IntWritable> {

    public void map(LongWritable key, Text line, Context context) 
            throws IOException, InterruptedException {
        String[] info = line.toString().split(",");
        // 第四列为country列
        context.write(new Text(info[3]), new IntWritable(1));
    }
}

public class OutReducer extends Reducer<Text, IntWritable, Text, IntWritable> {

    public void reduce(Text key, Iterable<IntWritable> values, Context context)
            throws IOException, InterruptedException {
        int count = 0;
        for (IntWritable  value: values) {
            count += value.get();
        }
        context.write(key, new IntWritable(count));
    }
}

public class OutRunner extends Configured implements Tool {

    public static void main(String[] args) {
        try {
            System.exit(ToolRunner.run(new OutRunner(), args));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public int run(String[] args) throws Exception {
        Job job = Job.getInstance(getConf(), "HQL");
        job.setJarByClass(getClass());

        FileInputFormat.addInputPath(job, new Path(args[0]));
        job.setInputFormatClass(TextInputFormat.class);

        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        job.setOutputFormatClass(TextOutputFormat.class);

        job.setMapperClass(OutMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        job.setReducerClass(OutReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        return job.waitForCompletion(true) ? 0 : 1;
    }
}

jar包和测试数据在这里QAQ