MR案例：WordCount改写

请参照wordcount实现一个自己的MapReduce，需求为：

    a. 输入文件格式：

       xxx,xxx,xxx,xxx,xxx,xxx,xxx

    b. 输出文件格式：

       xxx,20

       xxx,30

       xxx.40

    c. 功能：根据命令行参数统计输入文件中指定关键字出现的次数，并展示出来

       例如：hadoop jar xxxxx.jar keywordcount xxx,xxx,xxx,xxx(四个关键字）

package demo0830;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
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.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import java.io.IOException;
import java.util.ArrayList;

public class Demo0902 {
    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();

        if (args.length < 3) {
            System.out.println("Usage: wordcount <input_path> <output_path> <keyword_list>");
            return;
        }

        //Add to target(静态方法)
        String[] target_words = args[2].split(",");
        for (String word : target_words) {
            WCMap.addTargetWord(word.toLowerCase());
        }

        Job job = Job.getInstance(conf);
        job.setJarByClass(Demo0902.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        job.setMapperClass(WCMap.class);
        job.setReducerClass(WCReduce.class);

        job.setInputFormatClass(TextInputFormat.class);
        job.setOutputFormatClass(TextOutputFormat.class);

        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        job.waitForCompletion(true);
    }
    public static class WCMap extends Mapper<LongWritable, Text, Text, IntWritable> {

        private final static IntWritable one = new IntWritable(1);
        private Text word = new Text();
        private final static ArrayList<String> target_words = new ArrayList<String>();

        public static void addTargetWord(String word) {
            target_words.add(word);
        }

        public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String[] items = value.toString().toLowerCase().split(" ");
            for (String item : items) {

                //filter keyword
                if (target_words.contains(item)) {
                    word.set(item);
                    context.write(word, one);
                }
            }
        }
    }

    public static class WCReduce extends Reducer<Text, IntWritable, Text, IntWritable> {
        public void reduce(Text key, Iterable<IntWritable> values, Context context)
                throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            context.write(key, new IntWritable(sum));
        }
    }
}