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/share3.ls5.vim MyFSDataInputStream.java 7.javac -classpath /usr/local/hadoop/share/hadoop/common/hadoop-common-2.7.4.jar     MyFSDataInputStream.java       9.ls11.HADOOP_CLASSPATH=. hadoop MyFSDataInputStream

运行结果：

来源地址：https://blog.csdn.net/weixin_46390041/article/details/129805188