Support Java 7

[hrj]

Originally, we chose to convert to Java 8, because it appeared to be stable enough, and the lambda feature seemed convenient.

However, the reality is different now:

• It is hard to find openjdk-8 builds on all platforms. This hampers https support because Oracle builds don't enable advanced ciphers by default. See SSL handshake fails for servers with strong ciphers #11
• Checked exceptions make lambdas difficult to use (unlike in Scala). Also may classes don't expose a good functional interface (such as the Option) class, hampering the use of lambdas.

Hence, it might be worthwhile to convert code to be Java 7 compatible.

[hrj]

@vn971 Did you delete a comment here?

I think supporting Java 7 is not required / worthwhile anymore. Somethings have changed now:

• Azul Systems has released OpenJDK8 builds on all platforms, under GPL license. They also support strong ciphers (albeit as a separate download).
• The null analysis enabled by Java 8 type annotations is extremely useful.
• Writing functional code using lambdas is a bit cumbersome, but I later learnt that lambdas in Java 8 are more optimal than simple anonymous classes. So there's that.
• We are now using some Java 8 features such as Base64 class and couple of others.
• Java 7 has reached EOL. Security updates are now guranteed by only a few vendors (like RedHat).

So I think Java 8 is a good target as of today. Closing.

[hrj]

To add to the above list, we are using default methods in interfaces (a Java 8 feature).