12.20熟悉常用的HDFS操作2

（二）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。

import org.apache.hadoop.fs.FSDataInputStream;

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.io.IOException;

 

public class MyFSDataInputStream extends FSDataInputStream {

    private BufferedReader reader;

 

    public MyFSDataInputStream(FSDataInputStream in) throws IOException {

        super(in);

        this.reader = new BufferedReader(new InputStreamReader(in));

    }

 

    public String readLine() throws IOException {

        return reader.readLine();

    }

}

（三）查看Java帮助手册或其它资料，用“java.net.URL”和“org.apache.hadoop.fs.FsURLStreamHandlerFactory”编程完成输出HDFS中指定文件的文本到终端中。

import java.io.InputStream;

import java.net.URL;

import java.net.URLConnection;

 

public class HdfsFileReader {

    public static void main(String[] args) {

        try {

            URL url = new URL("hdfs://localhost:9000/user/hadoop/hdfsfile.txt");

            URLConnection connection = url.openConnection();

            InputStream inputStream = connection.getInputStream();

            int data = inputStream.read();

            while (data != -1) {

                System.out.print((char) data);

                data = inputStream.read();

            }

            inputStream.close();

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

}