Java set timezone at runtime
===

I am working on a desktop application. It would get input as a text file from user having contents like this :

<code>
    ..................................   
    ..................................

    Mon Jul  9 14:41:07 MDT 2012
    ..................................
    ..................................
    ..................................
</code>

I am using this information and creating a timeseries chart using jfreechart library.
Timezone could be anything available in the world. But when i use this file it's default timezone is sytem's timezone(IST) so doesn't show MDT time. When i tried to capture timezone from date and then used 

<code>    TimeZone.setDefault(TimeZone.getTimeZone("MDT"));</code> 

It didn't work. Can anyone please tell me how to change default timezone in java when i am having abbreviation for timezone like MDT, CDT etc....  