Collecting User-Follower data


I have a large database of twitter users (about 6 million). I have the user ids, login handle, their recent tweets, contact details, location etc.

I want to build a user-follower list out of these. Basically I want to create another table which will have two-columns - 1) User-ID (the id of the user which I have) 2) Follower-ID (the ids, separated by a semicolon - of all the followers of this user)

For example: if an user with id 001 is is being followed users with ids 002,003 the record would look like this -

User-ID - 001 Follower-ID - 002;003

I want to achieve this using Java preferably, but I am open to other languages as well.

I tried using twitter4j - a Java library to get tweets, users etc - but it has a limitation on number of API calls a day. Using the twitter SEARCH OR REST API is not possible since it does not give me the ids of the followers of a particular user.

How can I do this? Please help - I am doing this as a part of my research project and I am really stuck here.

Please help !