以一个上传文件的例子来说 DistributedFileSystem

public class UploadAndDown {

    public static void main(String[] args) {
        UploadAndDown uploadAndDown = new UploadAndDown();
        try {
            //将本地文件local.txt上传为HDFS上cloud.txt文件
            uploadAndDown.upLoadToCloud("local.txt", "cloud.txt");
            //将HDFS上的cloud.txt文件下载到本地cloudTolocal.txt文件
            uploadAndDown.downFromCloud("cloudTolocal.txt", "cloud.txt");
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void upLoadToCloud(String srcFileName, String cloudFileName)
            throws FileNotFoundException, IOException {
        // 本地文件存取的位置
        String LOCAL_SRC = "/home/linuxidc/hbase2/bin/" + srcFileName;
        // 存放到云端HDFS的位置
        String CLOUD_DEST = "hdfs://localhost:9000/user/linuxidc/" + cloudFileName;
        InputStream in = new BufferedInputStream(new FileInputStream(LOCAL_SRC));
        // 获取一个conf对象
        Configuration conf = new Configuration();
        // 文件系统
        FileSystem fs = FileSystem.get(URI.create(CLOUD_DEST), conf);
        // 输出流
        OutputStream out = fs.create(new Path(CLOUD_DEST), new Progressable() {
            @Override
            public void progress() {
                System.out.println("上传完成一个文件到HDFS");
            }
        });
        // 连接两个流，形成通道，使输入流向输出流传输数据
        IOUtils.copyBytes(in, out, 1024, true);
    }

    private void downFromCloud(String srcFileName, String cloudFileName) throws FileNotFoundException, IOException {
        // 云端HDFS上的文件
        String CLOUD_DESC = "hdfs://localhost:9000/user/linuxidc/"+cloudFileName;
        // down到本地的文件
        String LOCAL_SRC = "/home/linuxidc/hbase2/bin/"+srcFileName;
        // 获取conf配置
        Configuration conf = new Configuration();
        // 实例化一个文件系统
        FileSystem fs = FileSystem.get(URI.create(CLOUD_DESC), conf);
        // 读出流
        FSDataInputStream HDFS_IN = fs.open(new Path(CLOUD_DESC));
        // 写入流
        OutputStream OutToLOCAL = new FileOutputStream(LOCAL_SRC);
        // 将InputStrteam 中的内容通过IOUtils的copyBytes方法复制到OutToLOCAL中
        IOUtils.copyBytes(HDFS_IN, OutToLOCAL, 1024, true);
    }

}

  如图是个从远程向hadoop 文件系统上传文件的例子。