How to invoke SearchAds API by Java

I am planning to get Campaign data by invoking SearchAds API. According to the Search Ads API Reference, "API callers must establish two-way SSL authentications using client-side Certificates ".

At present, I have got two files of pem and key, but I don't know how to deal with them.

Anyone who has accessed the interface through Java can give me some hints or help?


Thanks.