Hello zhimakaimen, and welcome to the group. JBookTrader distribution already includes the compiled IB API, so you don't have to do anything extra with it. Furthermore, I'd advise you against making changes to the IB API. This is where the low level API implementation takes place, and you probably don't want to mess with it. Changing that code would also make it more difficult to upgrade to the future updated versions of IB API. If your intent to use JBookTrader to design, test, optimize, and test your own trading strategies, you source code modifications should be confined to the two packages:
com.jbooktrader.indicator and com.jbooktrader.strategy
The rest is already implemented and automated for you. If there is anything missing in JBT to facilitate your strategy design and development, please let us know.