If you are converting a timestamp value on a different machine, you should also check the timezone of that machine. For example;
The above decriptions will result different Date values, if you run with EST or UTC timezones.
To set the timezone; aka to UTC, you can simply rewrite;
TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
java.util.Date time= new java.util.Date((Long.parseLong(timestamp)*1000));