To build on what Manoj has described, there are few aspects to your usecase and 
cluster interaction from outside the cluster that you need to be aware of…

* If the cluster is secured - you will need to use SPNEGO - HttpClient does 
support this too
* if you need to invoke the REST APIs as each authenticated enduser rather than 
as a single identity representing the application then you will need your 
application to be configured as a trusted proxy to HDFS
* if you have the cluster firewalled off from the rest of your network then you 
will need to punch holes in the firewall for the host:ports that you need 
access to

You can simplify the above by use a reverse proxy like Apache Knox to be an API 
Gateway for the REST APIs that you need access to.
See http://knox.apache.org/ for more details.

On Jun 2, 2015, at 9:56 AM, Manoj Babu 
<[email protected]<mailto:[email protected]>> wrote:

Hi - You can invoke the REST service using HTTP request with help of any HTTP 
clients. Example if it is an Java web application you can use Apache commons 
HTTP client.

Thanks.

On Tuesday, June 2, 2015, Carmen Manzulli 
<[email protected]<mailto:[email protected]>> wrote:
Hi,
I would like to know hot to use WebHDFS methods of RESTful Web Services to open 
and read a file from a web application....instead of using curl!

For example, i would know ho to create a client and submit a Get HTTP request 
to the namenode.

Thanks in advance,

Carmen.


--
Cheers!
Manoj.


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