Support asynchronous server

[jovany-wang]

[jovany-wang]

I'd like to support this feature. Please let me know what your thought is.

[wenweihu86]

@jovany-wang This is a very useful feature.

[jovany-wang]

OK, I'll finish it in the next several weeks.

[jovany-wang]

@wenweihu86 I'd like to use CompletableFuture to support async server with its client. If this sounds good to you, I will send a simple document on this design.

Please let me know your thoughts, thanks.

[FoghostCn]

The simplest scenario can be considered as rpc proxy. async server may effectively improve throughput. CompletableFuture may be a good choice. Perhaps the async implementation in the client can also use CompleteFuture instead of callback

[jovany-wang]

@FoghostCn
Maybe it's better to support both of the callback client and CompletableFuture client.

Another issue is that we should upgrade the JDK version to 1.8+.

[chen-xl-dev]

Expect asynchrony on the server side. If the server has network operation, asynchronous server can bring more performance improvement. Take a look at joyrpc.