MapReduce——调用HDFS

调用HDFS文件接口实现对分布式文件系统中文件的访问，如创建、修改、删除等。

实验代码

package mapreduce;

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

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.Scanner;

public class test01 {
    private static FileSystem fs;
    private static Scanner input=new Scanner(System.in);
    //获取文件系统
    public static FileSystem init() throws URISyntaxException, IOException, InterruptedException {
        if(fs==null){
            Configuration conf = new Configuration();
            fs = FileSystem.get(new URI("hdfs://192.168.109.10:9000"),conf,"root");
        }
        return fs;
    }

    //关闭资源
    public void close() throws IOException {
        if(fs!=null){
            fs.close();
        }

    }

    //创建文件
    public static void createFile(String path) throws IOException, URISyntaxException, InterruptedException {
        fs=init();
        fs.create(new Path(path));
        if(isExist(path)){
            System.out.println("文件创建成功");
        }else {
            System.out.println("文件创建失败");
        }
    }

    //创建文件
    public static void deleteFile(String path) throws IOException, URISyntaxException, InterruptedException {
        fs=init();
        fs.delete(new Path(path),true);   //可递归删除
        if(!isExist(path)){
            System.out.println("文件删除成功");
        }else {
            System.out.println("文件删除失败");
        }
    }

    //向终端展示文件内容
    public static void showFile(String path) throws InterruptedException, IOException, URISyntaxException {
        fs=init();
        FSDataInputStream in = fs.open(new Path(path));
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(in));
        String content =  bufferedReader.readLine(); //读取文件一行
        while (content!=null){
            System.out.println(content);
            content=bufferedReader.readLine();
        }
        bufferedReader.close();
        in.close();
    }



    //向已有文件追加内容
    public static void appendFile(String path) throws IOException, URISyntaxException, InterruptedException {
        fs=init();
        System.out.println("追加前");
        showFile(path);

        System.out.println("请输入你想追加的内容");
        String content = input.next();
        FSDataOutputStream out = fs.append(new Path(path));
        out.write(content.getBytes());  //默认追加在末尾
        IOUtils.closeStream(out);

        System.out.println("追加后");
        showFile(path);
    }


    //判断文件是否存在
    public static boolean isExist(String path) throws IOException {
        return fs.exists(new Path(path));
    }



    public static void main(String[] args) throws IOException, URISyntaxException, InterruptedException {
        createFile("/wdy/test.txt");
        //deleteFile("/wdy/test.txt");
        //appendFile("/wdy/test.txt");

        fs.close();
    }

}