Archaius 0.x is not compatible with Java 6/7

[rkettelerij]

The following issue is currently causing issues in the spring-cloud project, since spring-cloud is currently based on spring 4.x which maintains compatibility with Java 7.

Archaius 0.x claims to be compatible with Java 6 (source and target versions are set to 1.6) but when calling com.netflix.config.ConcurrentMapConfiguration.getKeys under Java 7 the following exception occurs:

Caused by: java.lang.NoSuchMethodError: java.util.concurrent.ConcurrentHashMap.keySet()Ljava/util/concurrent/ConcurrentHashMap$KeySetView; at com.netflix.config.ConcurrentMapConfiguration.getKeys(ConcurrentMapConfiguration.java:152)

This is caused by the fact that Archaius 0.x is compiled using a JDK 8 with source/target set to 1.6 but without a bootclasspath set to 1.6. Therefore you'll run into this issue: https://gist.github.com/AlainODea/1375759b8720a3f9f094

I see three solutions:

• Switch to using JDK 1.6 or 1.7 entirely. This involves updating the Travis build config.
• Stay on JDK 8 but specify a bootclasspath. Dunno if this is possible with Travis.
• The quick 'n dirty fix in this PR, based on the idea set forth in https://gist.github.com/AlainODea/1375759b8720a3f9f094