Yes, you can build the library for the Mac OSX. You can follow the instructions at the github repo or do as follows :
$ git clone https://github.com/couchbase/couchbase-lite-java
$ cd couchbase-lite-java
$ git submodule init && git submodule update
$ ./gradlew build && ./gradlew distZip (The packaged file will be located at build/distributions)
Note that the XCode Command Line Tools is required to build the library. If you do not have it installed on your machine, you can download from https://developer.apple.com/downloads and install.
Is there a specific reason you want to use the Java library on Mac OS? Generally it’s preferable to use the native Objective-C version. The couchbase-lite-ios Xcode project has targets to build for Mac OS.
(Of course, if you’re building a Java app I can see why you’d need the Java library. But in that case it’s pretty likely that you’d be building your app on another platform.)