how to merge files inside meta-inf/services

In normal conditions, for maven users, fastest way to create uberJar that contains all of your dependencies is to use maven-assembly-plugin like the one below;

However, The problem with this usage is if you are calling ServiceLoader.loadServices , highly likely you will have more then one resource file with the same packaging, in this case shade plugin will suit you better to create uberJar as it is simply merges content of the same packages.