[Dubbo-3342]fixdubbo2.7.0 com.alibaba.com.caucho.hessian.io.HessianProtocolException: 'com.alibaba.dubbo.common.URL' could not be instantiated#3342

[CrazyHZM]

What is the purpose of the change

fix #3342

Brief changelog

XXXXX

Verifying this change

XXXXX

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[codecov-io]

Codecov Report

Merging #3345 into master will increase coverage by 0.04%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #3345      +/-   ##
============================================
+ Coverage     63.69%   63.74%   +0.04%     
  Complexity       71       71              
============================================
  Files           661      661              
  Lines         28617    28619       +2     
  Branches       4825     4825              
============================================
+ Hits          18229    18243      +14     
+ Misses         8170     8159      -11     
+ Partials       2218     2217       -1

Impacted Files	Coverage Δ	Complexity Δ
...le/src/main/java/com/alibaba/dubbo/common/URL.java	9.27% <0%> (-0.13%)	0 <0> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	58.69% <0%> (-8.7%)	0% <0%> (ø)
.../dubbo/remoting/transport/netty4/NettyChannel.java	61.17% <0%> (-4.71%)	0% <0%> (ø)
.../java/org/apache/dubbo/config/ReferenceConfig.java	56.45% <0%> (-0.37%)	0% <0%> (ø)
...rg/apache/dubbo/common/timer/HashedWheelTimer.java	58.18% <0%> (+0.34%)	0% <0%> (ø)	⬇️
...dubbo/remoting/exchange/support/DefaultFuture.java	70.94% <0%> (+1.35%)	0% <0%> (ø)	⬇️
...a/org/apache/dubbo/monitor/dubbo/DubboMonitor.java	89.71% <0%> (+1.86%)	0% <0%> (ø)	⬇️
...org/apache/dubbo/rpc/protocol/AbstractInvoker.java	66.12% <0%> (+3.22%)	0% <0%> (ø)	⬇️
...bo/rpc/cluster/support/FailbackClusterInvoker.java	70.49% <0%> (+3.27%)	0% <0%> (ø)	⬇️
...c/main/java/org/apache/dubbo/rpc/RpcException.java	86.2% <0%> (+3.44%)	0% <0%> (ø)	⬇️
... and 3 more

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[carryxyh]

duplicate with #3350
A protected constructor is better.