从下面的代码我不明白两件事： DistributedCache.addcachefile(new URI ('/.dat'), job.getconfiguration()) 我不明白uri路径必须存在于hdfs中。如果我错了，请纠正我。
那是什么 p.getname().equals() 从以下代码：

public class MyDC {
public static class MyMapper extends Mapper < LongWritable, Text, Text, Text > {
    private Map < String, String > abMap = new HashMap < String, String > ();
    private Text outputKey = new Text();
    private Text outputValue = new Text();
    protected void setup(Context context) throws
    java.io.IOException, InterruptedException {
        Path[] files = DistributedCache.getLocalCacheFiles(context.getConfiguration());
        for (Path p: files) {
            if (p.getName().equals("abc.dat")) {
                BufferedReader reader = new BufferedReader(new FileReader(p.toString()));
                String line = reader.readLine();
                while (line != null) {
                    String[] tokens = line.split("\t");
                    String ab = tokens[0];
                    String state = tokens[1];
                    abMap.put(ab, state);
                    line = reader.readLine();
                }
            }
        }
        if (abMap.isEmpty()) {
            throw new IOException("Unable to load Abbrevation data.");
        }
    }
    protected void map(LongWritable key, Text value, Context context)
    throws java.io.IOException, InterruptedException {
        String row = value.toString();
        String[] tokens = row.split("\t");
        String inab = tokens[0];
        String state = abMap.get(inab);
        outputKey.set(state);
        outputValue.set(row);
        context.write(outputKey, outputValue);
    }
}
public static void main(String[] args)
throws IOException, ClassNotFoundException, InterruptedException {
    Job job = new Job();
    job.setJarByClass(MyDC.class);
    job.setJobName("DCTest");
    job.setNumReduceTasks(0);
    try {
        DistributedCache.addCacheFile(new URI("/abc.dat"), job.getConfiguration());
    } catch (Exception e) {
        System.out.println(e);
    }
    job.setMapperClass(MyMapper.class);
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);
    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    job.waitForCompletion(true);
}
}