Hadoop REST API -- WebHDFS(下）

下面主要介绍几种常用的WebHDFS操作。

5.1 创建

     创建一个目录/tmp/webhdfs。

<span style="font-size:18px;">curl-i -X PUT"http://hadoop-master:14000/webhdfs/v1/tmp/webhdfs?user.name=app&op=MKDIRS"
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Set-Cookie:hadoop.auth="u=app&p=app&t=simple&e=1393356198808&s=74NhnIdH7WceKqgTW7UJ1ia9h10=";Version=1; Path=/
Content-Type: application/json
Transfer-Encoding: chunked
Date: Tue, 25 Feb 2014 09:23:23 GMT</span>

达到相似的功能，Hadoop 命令：

<span style="font-size:18px;">hdfs dfs -mkdir /tmp/webhdfs</span>

创建一个文件

 

创建一个文件需要两个步骤：第一步是在namenode运行命令，第二步根据第一步提供的location参数执行PUT操作。

<span style="font-size:18px;">curl -i -X PUT"http://hadoop-master:50070/webhdfs/v1/tmp/webhdfs/webhdfs-test.txt?user.name=app&op=CREATE"
HTTP/1.1 307 TEMPORARY_REDIRECT
Cache-Control: no-cache
Expires: Thu, 01-Jan-1970 00:00:00 GMT
Date: Wed, 26 Feb 2014 14:35:29 GMT
Pragma: no-cache
Date: Wed, 26 Feb 2014 14:35:29 GMT
Pragma: no-cache
Set-Cookie:hadoop.auth="u=app&p=app&t=simple&e=1393461329238&s=as2cO3rRtvj8psr0jAhMk6YBHRY=";Path=/
Location:http://machine-2:50075/webhdfs/v1/tmp/webhdfs/webhdfs-test.txt?op=CREATE&user.name=app&namenoderpcaddress=hadoop-master:9000&overwrite=false
Content-Type: application/octet-stream
Content-Length: 0
Server: Jetty(6.1.26)</span>

发送数据到指定文件中：

<span style="font-size:18px;">curl -i -X PUT -T webhdfs-test.txt"http://machine-2:50075/webhdfs/v1/tmp/webhdfs/webhdfs-test.txt?op=CREATE&user.name=app&namenoderpcaddress=hadoop-master:9000&overwrite=false"
HTTP/1.1 100 Continue
 
HTTP/1.1 201 Created
Cache-Control: no-cache
Expires: Wed, 26 Feb 2014 14:37:51 GMT
Date: Wed, 26 Feb 2014 14:37:51 GMT
Pragma: no-cache
Expires: Wed, 26 Feb 2014 14:37:51 GMT
Date: Wed, 26 Feb 2014 14:37:51 GMT
Pragma: no-cache
Location:webhdfs://0.0.0.0:50070/tmp/webhdfs/webhdfs-test.txt
Content-Type: application/octet-stream
Content-Length: 0
Server: Jetty(6.1.26)</span>

5.2 读取文件

    读取/input文件信息，使用-L参数。

<span style="font-size:18px;">[app@hadoop-master ~]$ curl -i -L"http://hadoop-master:14000/webhdfs/v1/input?op=OPEN&user.name=app"
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Set-Cookie:hadoop.auth="u=app&p=app&t=simple&e=1393420279602&s=dSnnx9oOwgGwVV/Q/ZmFyRjbtFU=";Version=1; Path=/
Content-Type: application/octet-stream
Content-Length: 1358
Date: Wed, 26 Feb 2014 03:11:19 GMT
Apache HBase [1] is an open-source,distributed, versioned, column-oriented
store modeled after Google' Bigtable: ADistributed Storage System for
Structured Data by Chang et al.[2]  Just as Bigtable leverages the distributed
data storage provided by the Google FileSystem, HBase provides Bigtable-like
capabilities on top of Apache Hadoop[3].
 
To get started using HBase, the fulldocumentation for this release can be
found under the doc/ directory thataccompanies this README.  Using abrowser,
open the docs/index.html to view theproject home page (or browse to [1]).
The hbase 'book' at docs/book.html has a'quick start' section and is where you
should being your exploration of thehbase project.
 
The latest HBase can be downloaded froman Apache Mirror [4].
 
The source code can be found at [5]
 
The HBase issue tracker is at [6]
 
Apache HBase is made available under theApache License, version 2.0 [7]
 
The HBase mailing lists and archives arelisted here [8].
 
1. http://hbase.apache.org
2.http://labs.google.com/papers/bigtable.html
3. http://hadoop.apache.org
4.http://www.apache.org/dyn/closer.cgi/hbase/
5.http://hbase.apache.org/docs/current/source-repository.html
6.http://hbase.apache.org/docs/current/issue-tracking.html
7.http://hbase.apache.org/docs/current/license.html
8. http://hbase.apache.org/docs/current/mail-lists.html</span>

 

5.3 重命名目录

   需要修改op的值和添加destination参数，实例如下所示：

<span style="font-size:18px;">[app@hadoop-master~]$ curl -i -X PUT
"http://hadoop-master:14000/webhdfs/v1/tmp/webhdfs?op=RENAME&user.name=app&destination=/tmp/webhdfs-new"
[app@hadoop-master~]$ curl -i -X PUT
"http://hadoop-master:14000/webhdfs/v1/tmp/webhdfs?op=RENAME&user.name=app&destination=/tmp/webhdfs-new"
HTTP/1.1 200 OK
Server:Apache-Coyote/1.1
Set-Cookie: hadoop.auth="u=app&p=app&t=simple&e=1393420506278&s=Oz9HEzxuYvP8kfAY4SWH6h+Gb50=";Version=1; Path=/
Content-Type:application/json
Transfer-Encoding:chunked
Date: Wed, 26 Feb2014 03:15:06 GMT
 
{"boolean":true}</span>

验证是否正确地执行，输入下列命令：

<span style="font-size:18px;">[app@hadoop-master~]$ hdfs dfs -ls /tmp
Found 5 items
drwx------   - app supergroup          0 2014-01-08 08:02 /tmp/hadoop-yarn
drwxr-xr-x   - app supergroup          0 2014-02-02 09:43 /tmp/hdfs_out
drwxr-xr-x   - app supergroup          0 2014-02-20 22:39 /tmp/hive-app
drwxr-xr-x   - app supergroup          0 2014-02-25 04:25 /tmp/jps
drwxr-xr-x   - app supergroup          0 2014-02-25 04:23 /tmp/webhdfs-new</span>

5.4 删除目录

非空的目录删除的话会抛出异常，只有为空的目录才会被删除。

<span style="font-size:18px;">[app@hadoop-master ~]$ curl -i -X DELETE
"http://hadoop-master:14000/webhdfs/v1/tmp/webhdfs-new?op=DELETE&user.name=app"
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Set-Cookie:hadoop.auth="u=app&p=app&t=simple&e=1393421161052&s=r03LOm2hO91ujcc66wNWyMJnDx4=";Version=1; Path=/
Content-Type: application/json
Transfer-Encoding: chunked
Date: Wed, 26 Feb 2014 03:26:01 GMT
 
{"boolean":true}</span>

核查是否正确地执行

<span style="font-size:18px;">[app@hadoop-master ~]$ hdfs dfs -ls /tmp
Found 4 items
drwx------   -app supergroup          0 2014-01-0808:02 /tmp/hadoop-yarn
drwxr-xr-x   -app supergroup          0 2014-02-0209:43 /tmp/hdfs_out
drwxr-xr-x   -app supergroup          0 2014-02-2022:39 /tmp/hive-app
drwxr-xr-x   -app supergroup          0 2014-02-2504:25 /tmp/jps</span>

总结

   WebDFS提供了一个简单、标准的方式来执行Hadoop 文件系统操作，这个客户端不必运行在Hadoop集群本身中。WebHDFS最主要的特性是让客户端通过预定义端口直接地链接namenode 和 datanode。这样的话，规避了好多HDFS proxy的代理层以及预先配置Tomcat的绑定。WebHDFD API是可互相交换的，这样让客户端不需要去打开防火墙端口。

两种常见的异常:

1. HTTP/1.1 405 HTTP method PUT is not supported by this URL

   修改hdfs-site.xml文件的权限属性。

<property>
<name>dfs.permissions</name>
<value>false</value>
</property>

2 {"RemoteException":{"exception":"AccessControlException","javaClassName":"org.apache.hadoop.security.AccessControlException","message":"Permission denied: user=dr.who, access=WRITE, inode=\"/qzhang\":Administrator:supergroup:drwxr-xr-x\n\tat

   问题2与问题1是一个问题，解决方案同上。