编程实现一个类“MyFSDataInputStream”

题目：编程实现一个类“MyFSDataInputStream”，该类继承“org.apache.hadoop.fs.FSDataInputStream”，要求如下：实现按行读取HDFS中指定文件的方法“readLine()”，如果读到文件末尾，则返回空，否则返回文件一行的文本。

1.	import java.io.IOException;
2.	import org.apache.hadoop.conf.Configuration;
3.	import org.apache.hadoop.fs.FileSystem;
4.	import org.apache.hadoop.fs.FSDataInputStream;
5.	import org.apache.hadoop.fs.Path;
6.	
7.	public class MyFSDataInputStream extends FSDataInputStream {
8.	    private static final int BUFFER_SIZE = 4096;
9.	    private byte[] buffer;
10.	    private int pos;
11.	    private int end;
12.	    private boolean eof;
13.	
14.	    public MyFSDataInputStream(FileSystem fs, Path file) throws IOException {
15.	        super(fs.open(file));
16.	        buffer = new byte[BUFFER_SIZE];
17.	        pos = 0;
18.	        end = 0;
19.	        eof = false;
20.	    }
21.	
22.	    public String readNextLine() throws IOException {
23.	        StringBuilder sb = new StringBuilder();
24.	        int b = -1;
25.	        boolean found = false;
26.	
27.	        while (!eof && !found) {
28.	            if (pos >= end) {
29.	                fillBuffer();
30.	            }
31.	            if (end == -1) {
32.	                eof = true;
33.	            }
34.	            while (pos < end) {
35.	                b = buffer[pos++];
36.	                if (b == '\r' || b == '\n') {
37.	                    found = true;
38.	                    break;
39.	                }
40.	                sb.append((char) b);
41.	            }
42.	        }
43.	
44.	        if (sb.length() == 0 && eof) {
45.	            return "";
46.	        } else {
47.	            return sb.toString();
48.	        }
49.	    }
50.	
51.	    private void fillBuffer() throws IOException {
52.	        end = in.read(buffer);
53.	        pos = 0;
54.	    }
55.	
56.	    public static void main(String[] args) throws IOException {
57.	        if (args.length < 1) {
58.	            System.err.println("Usage: MyFSDataInputStream ");
59.	            System.exit(1);
60.	        }
61.	
62.	        String filePath = args[0];
63.	
64.	        Configuration conf = new Configuration();
65.	        Path path = new Path(filePath);
66.	        FileSystem fs = FileSystem.get(path.toUri(), conf);
67.	
68.	        MyFSDataInputStream in = new MyFSDataInputStream(fs, path);
69.	        String line;
70.	        while ((line = in.readNextLine()) != null) {
71.	            System.out.println(line);
72.	        }
73.	        in.close();
74.	    }
75.	}

命令如下：

1.	cd /usr/local/hadoop/share
3.	ls
5.	vim MyFSDataInputStream.java 
7.	javac -classpath /usr/local/hadoop/share/hadoop/common/hadoop-common-2.7.4.jar     MyFSDataInputStream.java       
9.	ls
11.	HADOOP_CLASSPATH=. hadoop MyFSDataInputStream

运行结果：