Hadoop基础教程-第4章 HDFS的Java API（4.6 Java API应用）

程裕强

发布于 2022-05-06 18:36:59

2020

发布于 2022-05-06 18:36:59

文章被收录于专栏：大数据学习笔记大数据学习笔记

第4章 HDFS的Java API

4.6 Java API应用

4.6.1 上传文件

先在本地（客户端）一个文件，比如在D盘下新建一个word2.txt文件，内容随便写

test
node node
Hadoop Hadoop

在Eclipse中编写Java程序

package cn.hadron.hdfsDemo;
import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

public class PutFile {

    public static void main(String[] args) throws Exception{
        //本地文件路径
        String local="D:\\word2.txt";
        String dest="hdfs://192.168.80.131:9000/user/root/input/word2.txt";
        Configuration cfg=new Configuration();
        FileSystem fs=  FileSystem.get(URI.create(dest),cfg,"root");
        fs.copyFromLocalFile(new Path(local), new Path(dest));
        fs.close();
    }
}

再次说明，String dest="hdfs://192.168.80.131:9000/user/root/input/word2.txt"要与core-site.xml文件中的fs.defaultFS配置对应，其值是hdfs://node1:9000。由于本地Windows系统的hosts文件没有配置node1，所以这里需要IP地址表示。

执行结果

[root@node1 ~]# hdfs dfs -ls /user/root/input
Found 2 items
-rw-r--r--   3 root supergroup         30 2017-05-21 03:48 /user/root/input/word2.txt
-rw-r--r--   3 root supergroup         55 2017-05-17 10:32 /user/root/input/words.txt

补充： FileSystem fs= FileSystem.get(URI.create(dest),cfg,"root");语句中指定了root用户，这是因为Windows系统默认用户是Administrator。如果程序中不指定用户名root，则可能抛出异常：Permission denied: user=Administrator

Exception in thread "main" org.apache.hadoop.security.AccessControlException: Permission denied: user=Administrator

4.6.2 下载文件

package cn.hadron.hdfsDemo;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.IOException;
import java.net.URI;
public class GetFile {

    public static void main(String[] args) throws IOException {
        String hdfsPath="hdfs://192.168.80.131:9000/user/root/input/words.txt";
        String localPath="D:/copy_words.txt";
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
        Path hdfs_path = new Path(hdfsPath);
        Path local_path = new Path(localPath);
        fs.copyToLocalFile(hdfs_path, local_path);
        fs.close();
    }
}

4.6.3 创建HDFS目录

package cn.hadron.hdfsDemo;

import java.net.URI; 
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

public class CreateDir {
    public static void main(String[] args) throws Exception {
        String url = "hdfs://192.168.80.131:9000/tmp/";
        Configuration conf = new Configuration();
        FileSystem fs=  FileSystem.get(URI.create(url),conf,"root");
        boolean b=fs.mkdirs(new Path(url));
        System.out.println(b);
        fs.close();
    }
}

[root@node1 ~]# hdfs dfs -ls /
Found 3 items
drwxr-xr-x   - root supergroup          0 2017-05-14 09:40 /abc
drwxr-xr-x   - root supergroup          0 2017-05-21 04:38 /tmp
drwxr-xr-x   - root supergroup          0 2017-05-14 09:37 /user

4.6.4 删除HDFS文件或文件夹

先上传一个文件到HDFS的/tmp目录

[root@node1 ~]# hdfs dfs -put /root/words.txt /tmp
[root@node1 ~]# hdfs dfs -ls /tmp
Found 1 items
-rw-r--r--   3 root supergroup         55 2017-05-21 04:57 /tmp/words.txt

package cn.hadron.hdfsDemo;

import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class DeleteFile {
    public static void main(String[] args) throws Exception{
        String uri = "hdfs://192.168.80.131:9000/tmp";
        Configuration conf = new Configuration();
        FileSystem fs =FileSystem.get(URI.create(uri),conf,"root");
        //参数true表示递归删除文件夹及文件夹下的文件
        boolean b = fs.delete(new Path(uri), true);
        System.out.println(b);
        fs.close();
    }
}

通过命令查看HDFS目录，显然HDFS的/tmp目录已经被删除

[root@node1 ~]# hdfs dfs -ls /
Found 2 items
drwxr-xr-x   - root supergroup          0 2017-05-14 09:40 /abc
drwxr-xr-x   - root supergroup          0 2017-05-14 09:37 /user

4.6.5 下载HDFS目录

package cn.hadron.hdfsDemo;
import java.io.IOException;
import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class CopyToLocalFile {
    public static void main(String[] args) throws IOException {
        String hdfsPath="hdfs://192.168.80.131:9000/user/root/input";
        String localPath="D:\\input";
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
        Path hdfs_path = new Path(hdfsPath);
        Path local_path = new Path(localPath);
        fs.copyToLocalFile(hdfs_path,local_path);
        fs.close();
    }
}

在D盘可以查看到input目录文件

其中.crc文件是校验文件。Hadoop系统为了保证数据的一致性，会对文件生成相应的校验文件，并在读写的时候进行校验，确保数据的准确性。

4.6.6 上传本地目录（文件夹）

先在本地准备一个待上传的目录，这里将刚才下载的input目录重命名为words，并删除.crc校验文件

package cn.hadron.hdfsDemo;

import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class CopyFromLocalFile {
    public static void main(String[] args) throws Exception{
        String hdfsPath="hdfs://192.168.80.131:9000/user/root/";
        String localPath="D:\\words";
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf,"root");
        Path hdfs_path = new Path(hdfsPath);
        Path local_path = new Path(localPath);
        fs.copyFromLocalFile(local_path, hdfs_path);
        fs.close();

    }
}

[root@node1 ~]# hdfs dfs -ls /user/root
Found 2 items
drwxr-xr-x   - root supergroup          0 2017-05-21 03:48 /user/root/input
drwxr-xr-x   - root supergroup          0 2017-05-21 05:21 /user/root/words
[root@node1 ~]# hdfs dfs -ls /user/root/words
Found 2 items
-rw-r--r--   3 root supergroup         30 2017-05-21 05:21 /user/root/words/word2.txt
-rw-r--r--   3 root supergroup         55 2017-05-21 05:21 /user/root/words/words.txt

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原始发表：2017-05-20，如有侵权请联系 cloudcommunity@tencent.com 删除

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