Hadoop编程调用HDFS
前言HDFS 全称Hadoop分步文件系统(Hadoop Distributed File System)，是Hadoop的核心部分之一。要实现MapReduce的分步式算法时，数据必需提前放在HDFS上。因此，对于HDFS的操作就变得非常重要。Hadoop的命令行，提供了一套完整命令接口，就像Linux命令一样方便使用。
不过，有时候我们还需要在程序中直接访问HDFS，我们可以通过API的方式进行HDFS操作。
目录
[*]系统环境
[*]ls操作
[*]rmr操作
[*]mkdir操作
[*]copyFromLocal操作
[*]cat操作
[*]copyToLocal操作
[*]创建一个新文件，并写入内容
1. 系统环境
Hadoop集群环境
[*]Linux Ubuntu 64bit Server 12.04.2 LTS
[*]Java 1.6.0_29
[*]Hadoop 1.1.2
如何搭建Hadoop集群环境？ 请参考文章：Hadoop历史版本安装
开发环境
[*]Win7 64bit
[*]Java 1.6.0_45
[*]Maven 3
[*]Hadoop 1.1.2
[*]Eclipse Juno Service Release 2
如何用Maven搭建Win7的Hadoop开发环境？ 请参考文章：用Maven构建Hadoop项目
注：hadoop-core-1.1.2.jar，已重新编译，已解决了Win远程调用Hadoop的问题，请参考文章：Hadoop历史版本安装
Hadooop命令行：java FsShell
~ hadoop fs
Usage: java FsShell
[-ls ]
[-lsr ]
[-du ]
[-dus ]
[-count[-q] ]
[-mv]
[-cp]
[-rm [-skipTrash] ]
[-rmr [-skipTrash] ]
[-expunge]
[-put... ]
[-copyFromLocal... ]
[-moveFromLocal... ]
[-get [-ignoreCrc] [-crc]]
[-getmerge ]
[-cat ]
[-text ]
[-copyToLocal [-ignoreCrc] [-crc]]
[-moveToLocal [-crc]]
[-mkdir ]
[-setrep [-R] [-w]]
[-touchz ]
[-test - ]
[-stat ]
[-tail [-f] ]
[-chmod [-R] <mode[,mode]... |="" octalmode="" style="margin: 0pt; padding: 0pt;"> PATH...]
[-chown [-R] [:] PATH...]
[-chgrp [-R] GROUP PATH...]
[-help ]
上面列出了30个命令，我只实现了一部分的HDFS的命令！
新建文件：HdfsDAO.java，用来调用HDFS的API。
public class HdfsDAO {
//HDFS访问地址
private static final String HDFS = "hdfs://192.168.1.210:9000/";
public HdfsDAO(Configuration conf) {
this(HDFS, conf);
}
public HdfsDAO(String hdfs, Configuration conf) {
this.hdfsPath = hdfs;
this.conf = conf;
}
//hdfs路径
private String hdfsPath;
//Hadoop系统配置
private Configuration conf;
//启动函数
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.mkdirs("/tmp/new/two");
hdfs.ls("/tmp/new");
}
//加载Hadoop配置文件
public static JobConf config(){
JobConf conf = new JobConf(HdfsDAO.class);
conf.setJobName("HdfsDAO");
conf.addResource("classpath:/hadoop/core-site.xml");
conf.addResource("classpath:/hadoop/hdfs-site.xml");
conf.addResource("classpath:/hadoop/mapred-site.xml");
return conf;
}
//API实现
public void cat(String remoteFile) throws IOException {...}
public void mkdirs(String folder) throws IOException {...}
...
}
2. ls操作
说明：查看目录文件
对应Hadoop命令：
~ hadoop fs -ls /
Found 3 items
drwxr-xr-x - conan supergroup 0 2013-10-03 05:03 /home
drwxr-xr-x - Administrator supergroup 0 2013-10-03 13:49 /tmp
drwxr-xr-x - conan supergroup 0 2013-10-03 09:11 /user
Java程序:
public void ls(String folder) throws IOException {
Path path = new Path(folder);
FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
FileStatus[] list = fs.listStatus(path);
System.out.println("ls: " + folder);
System.out.println("==========================================================");
for (FileStatus f : list) {
System.out.printf("name: %s, folder: %s, size: %d\n", f.getPath(), f.isDir(), f.getLen());
}
System.out.println("==========================================================");
fs.close();
}
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.ls("/");
}
控制台输出：
ls: /
==========================================================
name: hdfs://192.168.1.210:9000/home, folder: true, size: 0
name: hdfs://192.168.1.210:9000/tmp, folder: true, size: 0
name: hdfs://192.168.1.210:9000/user, folder: true, size: 0
==========================================================
3. mkdir操作
说明：创建目录，可以创建多级目录
对应Hadoop命令：
~ hadoop fs -mkdir /tmp/new/one
~ hadoop fs -ls /tmp/new
Found 1 items
drwxr-xr-x - conan supergroup 0 2013-10-03 15:35 /tmp/new/one
Java程序:
public void mkdirs(String folder) throws IOException {
Path path = new Path(folder);
FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
if (!fs.exists(path)) {
fs.mkdirs(path);
System.out.println("Create: " + folder);
}
fs.close();
}
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.mkdirs("/tmp/new/two");
hdfs.ls("/tmp/new");
}
控制台输出：
Create: /tmp/new/two
ls: /tmp/new
==========================================================
name: hdfs://192.168.1.210:9000/tmp/new/one, folder: true, size: 0
name: hdfs://192.168.1.210:9000/tmp/new/two, folder: true, size: 0
==========================================================
4. rmr操作
说明：删除目录和文件
对应Hadoop命令：
~ hadoop fs -rmr /tmp/new/one
Deleted hdfs://master:9000/tmp/new/one
~hadoop fs -ls /tmp/new
Found 1 items
drwxr-xr-x - Administrator supergroup 0 2013-10-03 15:38 /tmp/new/two
Java程序:
public void rmr(String folder) throws IOException {
Path path = new Path(folder);
FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
fs.deleteOnExit(path);
System.out.println("Delete: " + folder);
fs.close();
}
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.rmr("/tmp/new/two");
hdfs.ls("/tmp/new");
}
控制台输出：
Delete: /tmp/new/two
ls: /tmp/new
==========================================================
==========================================================
5. copyFromLocal操作
说明：复制本地文件系统到HDFS
对应Hadoop命令：
~ hadoop fs -copyFromLocal /home/conan/datafiles/item.csv /tmp/new/
~ hadoop fs -ls /tmp/new/
Found 1 items
-rw-r--r-- 1 conan supergroup 210 2013-10-03 16:07 /tmp/new/item.csv
Java程序:
public void copyFile(String local, String remote) throws IOException {
FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
fs.copyFromLocalFile(new Path(local), new Path(remote));
System.out.println("copy from: " + local + " to " + remote);
fs.close();
}
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.copyFile("datafile/randomData.csv", "/tmp/new");
hdfs.ls("/tmp/new");
}
控制台输出：
copy from: datafile/randomData.csv to /tmp/new
ls: /tmp/new
==========================================================
name: hdfs://192.168.1.210:9000/tmp/new/item.csv, folder: false, size: 210
name: hdfs://192.168.1.210:9000/tmp/new/randomData.csv, folder: false, size: 36655
==========================================================
6. cat操作
说明：查看文件内容
对应Hadoop命令：
~ hadoop fs -cat /tmp/new/item.csv
1,101,5.0
1,102,3.0
1,103,2.5
2,101,2.0
2,102,2.5
2,103,5.0
2,104,2.0
3,101,2.5
3,104,4.0
3,105,4.5
3,107,5.0
4,101,5.0
4,103,3.0
4,104,4.5
4,106,4.0
5,101,4.0
5,102,3.0
5,103,2.0
5,104,4.0
5,105,3.5
5,106,4.0
Java程序:
public void cat(String remoteFile) throws IOException {
Path path = new Path(remoteFile);
FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
FSDataInputStream fsdis = null;
System.out.println("cat: " + remoteFile);
try {
fsdis =fs.open(path);
IOUtils.copyBytes(fsdis, System.out, 4096, false);
} finally {
IOUtils.closeStream(fsdis);
fs.close();
}
}
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.cat("/tmp/new/item.csv");
}
控制台输出：
cat: /tmp/new/item.csv
1,101,5.0
1,102,3.0
1,103,2.5
2,101,2.0
2,102,2.5
2,103,5.0
2,104,2.0
3,101,2.5
3,104,4.0
3,105,4.5
3,107,5.0
4,101,5.0
4,103,3.0
4,104,4.5
4,106,4.0
5,101,4.0
5,102,3.0
5,103,2.0
5,104,4.0
5,105,3.5
5,106,4.0
7. copyToLocal操作
说明：从HDFS复制文件在本地操作系
对应Hadoop命令：
~ hadoop fs -copyToLocal /tmp/new/item.csv /home/conan/datafiles/tmp/
~ ls -l /home/conan/datafiles/tmp/
-rw-rw-r-- 1 conan conan 210 Oct3 16:16 item.csv
Java程序:
public void download(String remote, String local) throws IOException {
Path path = new Path(remote);
FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
fs.copyToLocalFile(path, new Path(local));
System.out.println("download: from" + remote + " to " + local);
fs.close();
}
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.download("/tmp/new/item.csv", "datafile/download");
File f = new File("datafile/download/item.csv");
System.out.println(f.getAbsolutePath());
}
控制台输出：
2013-10-12 17:17:32 org.apache.hadoop.util.NativeCodeLoader
警告: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
download: from/tmp/new/item.csv to datafile/download
D:\workspace\java\myMahout\datafile\download\item.csv
8. 创建一个新文件，并写入内容
说明：创建一个新文件，并写入内容。
[*]touchz:可以用来创建一个新文件，或者修改文件的时间戳。
[*]写入内容没有对应命令。
对应Hadoop命令：
~ hadoop fs -touchz /tmp/new/empty
~ hadoop fs -ls /tmp/new
Found 3 items
-rw-r--r-- 1 conan supergroup 0 2013-10-03 16:24 /tmp/new/empty
-rw-r--r-- 1 conan supergroup 210 2013-10-03 16:07 /tmp/new/item.csv
-rw-r--r-- 3 Administrator supergroup 36655 2013-10-03 16:09 /tmp/new/randomData.csv
~ hadoop fs -cat /tmp/new/empty
Java程序:
public void createFile(String file, String content) throws IOException {
FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);
byte[] buff = content.getBytes();
FSDataOutputStream os = null;
try {
os = fs.create(new Path(file));
os.write(buff, 0, buff.length);
System.out.println("Create: " + file);
} finally {
if (os != null)
os.close();
}
fs.close();
}
public static void main(String[] args) throws IOException {
JobConf conf = config();
HdfsDAO hdfs = new HdfsDAO(conf);
hdfs.createFile("/tmp/new/text", "Hello world!!");
hdfs.cat("/tmp/new/text");
}
控制台输出：
Create: /tmp/new/text
cat: /tmp/new/text
Hello world!!
完整的文件：HdfsDAO.java
https://github.com/bsspirit/maven_mahout_template/blob/mahout-0.8/src/main/java/org/conan/mymahout/hdfs/HdfsDAO.java
转自：
http://blog.fens.me/hadoop-hdfs-api/
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