用JAVA API实现HDFS常用shell命令的功能（新建文件夹，上传文件，下载文件，判断文件是否存在）

• 新建文件夹

package hdfs.files;

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

import java.io.IOException;

public class HDFSMKdir {
    public static void main(String[] args) throws IOException {
        //设置root权限
        System.setProperty("HADOOP_USER_NAME", "root");
        //创建HDFS连接对象client
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://yy001:9000");
        FileSystem client = FileSystem.get(conf);
        //在HDFS的根目录下创建aadir
        client.mkdirs(new Path("/aadir"));
        //关闭连接对象
        client.close();
        //输出"successful!"
        System.out.println("successfully!");
    }
}

• 上传文件

package hdfs.files;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class HDFSUpload {
    //声明输入流、输出流
    private static InputStream input;
    private static OutputStream output;

    public static void main(String[] args) throws IOException {
        //设置root权限
        System.setProperty("HADOOP_USER_NAME", "root");
        //创建HDFS连接对象client
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://yy001:9000");
        FileSystem client = FileSystem.get(conf);
        //创建本地文件的输入流
        input = new FileInputStream("D:\\aa.txt");
        //创建HDFS的输出流
        output = client.create(new Path("/a.txt"));
        //写文件到HDFS
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = input.read(buffer)) != -1) {
            output.write(buffer, 0, len);
        }
        //防止输出数据不完整
        output.flush();
        //使用工具类IOUtils上传或下载
        //IOUtils.copy(input, output);
        //关闭输入输出流
        input.close();
        output.close();
        System.out.println("成功！");
    }
}

• 下载文件

package hdfs.files;

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

import java.io.*;

public class HDFSDownload {
    //声明输入流、输出流
    private static InputStream input;
    private static OutputStream output;

    public static void main(String[] args) throws IOException {
        //设置root权限
        System.setProperty("HADOOP_USER_NAME", "root");
        //创建HDFS连接对象client
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://yy001:9000");
        FileSystem client = FileSystem.get(conf);
        //创建本地文件的输出流
        output = new FileOutputStream("d:\\cccout.txt");
        //创建HDFS的输入流
        input = client.open(new Path("/aadir/aaout.txt"));
        //写文件到HDFS
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = input.read(buffer)) != -1) {
            output.write(buffer, 0, len);
        }
        //防止输出数据不完整
        output.flush();
        //使用工具类IOUtils上传或下载
        //IOUtils.copy(input, output);
        //关闭输入输出流
        input.close();
        output.close();
        System.out.println("成功！");
    }
}

• 判断文件是否存在

package hdfs.files;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.IOException;
public class HDFSFileIfExist {
    public static void main(String[] args) throws IOException {
        //设置root权限
        System.setProperty("HADOOP_USER_NAME", "root");
        //创建HDFS连接对象client
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://yy001:9000");
        FileSystem client = FileSystem.get(conf);
        //声明文件对象
        String fileName = "/aadir/aaout.txt";
        //判断文件是否存在
        if (client.exists(new Path(fileName))) {
            System.out.println("文件存在！");
        } else {
            System.out.println("文件不存在！");
        }
    }
    
}