Improve several map iteration

[biyuhao]

What is the purpose of the change

Improve several places of map iteration

In JavaBeanSerializeUtil.java, Menu.java, DefaultFuture.java and several Test cases,
we have some code similar to

for (Key key : map.KeySet()) {
  Value value = map.get(key);
  ......
}

This pr will replace it using entrySet()

Brief changelog

source code and test code updated

Verifying this change

ut passwd

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[codecov-io]

Codecov Report

Merging #2938 into master will decrease coverage by 0.01%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master    #2938      +/-   ##
==========================================
- Coverage   63.73%   63.72%   -0.02%     
==========================================
  Files         578      578              
  Lines       25959    25958       -1     
  Branches     4544     4542       -2     
==========================================
- Hits        16546    16541       -5     
- Misses       7241     7244       +3     
- Partials     2172     2173       +1

Impacted Files	Coverage Δ
...e/dubbo/common/beanutil/JavaBeanSerializeUtil.java	79.31% <100%> (-0.08%)	⬇️
...dubbo/remoting/exchange/support/DefaultFuture.java	67.78% <33.33%> (ø)	⬆️
.../remoting/transport/netty4/NettyClientHandler.java	75% <0%> (-11.12%)	⬇️
...in/java/org/apache/dubbo/common/utils/JVMUtil.java	73.58% <0%> (-7.55%)	⬇️
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0%> (-4.35%)	⬇️
...he/dubbo/remoting/transport/netty/NettyServer.java	67.85% <0%> (-3.58%)	⬇️
...rg/apache/dubbo/common/timer/HashedWheelTimer.java	58.88% <0%> (-1.75%)	⬇️
...he/dubbo/registry/multicast/MulticastRegistry.java	65.51% <0%> (+1.72%)	⬆️
...rpc/protocol/dubbo/telnet/InvokeTelnetHandler.java	57.95% <0%> (+3.4%)	⬆️
...e/dubbo/remoting/transport/netty/NettyChannel.java	62.35% <0%> (+4.7%)	⬆️
... and 1 more

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[beiwei30]

@biyuhao, In my own opinion, it's nothing but code style. Both ways look good to me. Would you mind shine some light on me why your proposed way is better?

[biyuhao]

@beiwei30
I think this makes us a more unified code style and gain a better performance.
I did a little google search and got some betters answers than mine.

1. "entrySet()" should be iterated when both the key and value are needed
   

When only the keys from a map are needed in a loop, iterating the keySet makes sense. But when both the key and the value are needed, it's more efficient to iterate the entrySet, which will give access to both the key and value, instead.

2. Performance Comparison of Different Ways to Iterate over HashMap

Using entrySet() in for-each loop : 50
Using keySet() in for-each loop : 76
Using entrySet() and iterator : 50
Using keySet() and iterator : 75

3. performance-considerations-for-keyset-and-entryset-of-map

Here you first need to get hold of the set of keys. This takes time proportional to the capacity of the map (as opposed to size for the LinkedHashMap). After this is done, you call get() once for each key. Sure, in the average case, with a good hashCode-implementation this takes constant time. However, it will inevitably require lots of .hashCode and .equals calls, which will obviously take more time than just doing a entry.value() call.

At last, I have not done such a profiling. So I think it's more about unifying code style here.
This is a trivial change, it's on your call. 😃