Guava - set of core libraries that includes new collection types (such as multimap and multiset), immutable collections, a graph library, functional types, an in-memory cache, and APIs/utilities for concurrency, I/O, hashing, primitives, reflection, string processing and much more.
ProGuard rules for Guava
ProGuard will try to remove all dead code. After ProGuard shrinks and obfuscates code, short names like 'a', 'b', etc. are used as obfuscated names. You have to set up a ProGuard configuration in your proguard-rules.pro file.
-dontwarn java.lang.ClassValue -dontwarn com.google.common.base.** -dontwarn com.google.errorprone.annotations.** -dontwarn com.google.j2objc.annotations.** -dontwarn org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
For more information about Guava please see the website.