Not sure why no one mentioned this, but there is a Java DDP client library:
https://github.com/kutrumbo/java-ddp-client
FYI, I've forked this and fleshed it out quite a bit. I started writing an Android app with it and found it missing a lot of stuff to get it to work properly:
https://github.com/kenyee/java-ddp-client
I also wrote up an Android layer over this to make things easier and will check it into Github as soon as I figure out how to get it to work w/ Gradle in Eclipse (can't get it to recognize the android-libraries plugin so none of the references to the Android library work)-:
I did write an Android app using all this stuff...look in the Play store for "Meteor.js Party" which matches Meteor's Parties sample.