实验2的两道Java编程《大数据技术原理与应用》第3版

1.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 java.io.*;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

public class MyFSDataInputStream extends FSDataInputStream{

	public MyFSDataInputStream(InputStream in) {
		super(in);
		// TODO Auto-generated constructor stub
	}

	public static String readline(BufferedReader br) throws IOException {
		char[] data = new char[1024];
		int read = -1;
		int off = 0;
		while((read = br.read(data,off,1))!=-1) {
			if(String.valueOf(data[off+1]).equals("n")) break;
			off += 1;
		}
		if(off > 0) return String.valueOf(data);
		else return null;
	}
	
	public static void cat(Configuration conf , String remoteFilePath) throws IOException {
		FileSystem fs = FileSystem.get(conf);
		Path remotePath = new Path(remoteFilePath);
		FSDataInputStream in = fs.open(remotePath);
		BufferedReader br = new BufferedReader(new InputStreamReader(in));
		String line = null;
		while((line = MyFSDataInputStream.readline(br))!=null) {
			System.out.println(line);
		}
		br.close();
		in.close();
		fs.close();
	}
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Configuration conf = new Configuration();
		conf.set("fs.default.name", "hdfs://localhost:9000");
		String remoteFilePath = "/user/hadoop/merge.txt";
		try {
			MyFSDataInputStream.cat(conf, remoteFilePath);
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}

}

2.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.*;
import java.net.URL;

import org.apache.hadoop.fs.FsUrlStreamHandlerFactory;
import org.apache.hadoop.io.IOUtils;

public class ShowTheContent {

	public void show(String remotPath) {
		// TODO Auto-generated method stub
		try {
			FsUrlStreamHandlerFactory fsUrl = new FsUrlStreamHandlerFactory();
			URL.setURLStreamHandlerFactory(fsUrl);
			InputStream in = new URL("hdfs","localhost",9000,remotPath).openStream();
			IOUtils.copyBytes(in, System.out, 4096,false);
			IOUtils.closeStream(in);
//			BufferedReader br = new BufferedReader(new InputStreamReader(in));
//			String line = null;
//			while ((line = br.readLine())!=null) {
//				System.out.println(line);
//				
//			}
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
		
	}
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ShowTheContent s = new ShowTheContent();
		s.show("/user/hadoop/merge.txt");
	}

}