import org.apache.hadoop.fs.FileSystem;

FileSystem fs = FileSystem.get(conf);

import org.apache.hadoop.conf.Configuration;

Configuration conf = new Configuration();    

　　　　Path f = new Path("hdfs://hadoopH1:9000/jdk-7u80-linux-x64.tar.gz"); //指定路径
　　　　FSDataInputStream in = fs.open(f); //打开hdfs输入流

    FileOutputStream out = new FileOutputStream("/home/hadoop/Download/jdk.tar.gz");    //打开文件输出流，输入文件路径
    IOUtils.copy(in, out);

package cn.hadoop.hdfs;

import java.io.FileOutputStream;
import java.io.IOException;

import org.apache.commons.io.IOUtils;
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 HdfsBase {

    public static void main(String[] args) throws IOException {
        
        //要访问hdfs，需要获取FileSystem类（必须是org.apache.hadoop.fs包下）的实例对象
        Configuration conf = new Configuration();    
        FileSystem fs = FileSystem.get(conf);    //fs对象就是HDFS的客户端，用fs就可以读文件，写文件，查看文件...
        
        //下载文件
        Path f = new Path("hdfs://hadoopH1:9000/jdk-7u80-linux-x64.tar.gz");    //指定路径
        FSDataInputStream in = fs.open(f);    //打开hdfs输入流
        
        FileOutputStream out = new FileOutputStream("E:\\jdk.tar.gz");    //打开文件输出流，输入文件路径
        IOUtils.copy(in, out);
        //上传数据到hdfs文件系统
    }

}

    public void upload() throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://hadoopH1:9000/");
        FileSystem fs = FileSystem.get(conf);
        
        Path f = new Path("hdfs://hadoopH1:9000/Day01/linux-2.6.tar.gz");
        FSDataOutputStream out = fs.create(f);
        
        FileInputStream in = new FileInputStream("E:\\源码\\linux-2.6.19.tar.gz");
        IOUtils.copy(in, out);    //上传数据
    }

-DHADOOP_USER_NAME=hadoop

    public void upload2() throws IOException, InterruptedException, URISyntaxException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://hadoopH1:9000/");
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoopH1:9000/"),conf,"hadoop");
        
        fs.copyFromLocalFile(new Path("E:\\源码\\linux-2.6.19.tar.gz"), new Path("hdfs://hadoopH1:9000/Day01/linux2.6.taz"));
    }

    public void mkdir() throws IOException, InterruptedException, URISyntaxException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://hadoopH1:9000/");
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoopH1:9000/"),conf,"hadoop");
        
        fs.mkdirs(new Path("/new/dir/"));
    }

    public void rm() throws IOException, InterruptedException, URISyntaxException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://hadoopH1:9000/");
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoopH1:9000/"),conf,"hadoop");
        
        fs.delete(new Path("/new"), true);    //可以设置是否递归删除
    }