Remove guava and use java 8 constructs (#1082)

[copa2]

This PR removes the guava library dependency with java 8 constructs.
(Fix issue #1082)

The main reason is that other code also uses guava in a incompatible version and guava is not always binary compatible.

Incompatiblilites:

• This will update jdk from 1.6 to 1.8 as minimum version
• Binary incompatiblities
• Public API changes where guava constructs have been exposed

What is missing:

• Documentation updates (will follow / references to guava)
• Cleanups (Predicates, Function can be written more compact with java 8)

Checked alternatives:

• Using shading plugin to shade guava. This makes each sub-project artifact big due whole guava library has to be shaded into the artifact.

[dilipkrish]

Thank you @copa2. Will definitely pull in this change after the 2.8.0 release. Currently the library supports down to java 6 and this is a breaking change => up rev to 3.0.0 after this release.

[copa2]

Hi dilipkrish

Just checked the failure I receive from circleci.
Problem is that the CachingOperationReader already today is probably not doing what is expected.

springfox/springfox-spring-web/src/main/java/springfox/documentation/spring/web/scanners/CachingOperationReader.java

Line 57 in ec9af57

return cache.getUnchecked(new OperationCachingEquivalence().wrap(outerContext));

Each entry receives a new OperationCachingEquivalence which calls the Wrapper.
Within the Wrapper the equals checks if the Equivalence is the same Object
if (this.equivalence.equals(that.equivalence)) { before it calls doEquivalent. So all entries will never be equal an no caching will take place today.

Normally you only create one Equivalence object and then call wrap on the same. If I change the code on master like this i will get the same failure. To fix it properly we should probably reconsider what is equivalent for the Operation. Currently it fails in the PetStoreResource for getPetInTx and getPetInCA. It is looked equivalent, as the key data is the same. Probably we have additionally to check the static params or use the methodName. Any suggestions?

[copa2]

This PR is replaced by PR #2086, due unneeded crlf.