enhancement: use constructor injection instead of field injection

[kezhenxu94]

This patch uses Constructor Injection to avoid the drawbacks of Field Injection. What's more, Spring Documentation also recommends using Constructor Injection here

Here are some of the drawbacks of Field Injection listed in this article:

• Disallows immutable field declaration

• Eases single responsibility principle violation

• Tightly coupled with dependency injection container

• Hidden dependencies

[codecov-io]

Codecov Report

Merging #1839 into master will increase coverage by 1.55%.
The diff coverage is 95.2%.

@@             Coverage Diff              @@
##             master    #1839      +/-   ##
============================================
+ Coverage     48.31%   49.87%   +1.55%     
- Complexity     1913     1914       +1     
============================================
  Files           394      394              
  Lines         11680    12075     +395     
  Branches       1225     1225              
============================================
+ Hits           5643     6022     +379     
- Misses         5590     5606      +16     
  Partials        447      447

Impacted Files	Coverage Δ	Complexity Δ
.../apollo/portal/service/PortalDBPropertySource.java	29.41% <ø> (ø)	3 <0> (ø)	⬇️
...k/apollo/portal/component/RestTemplateFactory.java	100% <ø> (ø)	5 <0> (ø)	⬇️
...k/apollo/common/datasource/TitanEntityManager.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../apollo/portal/spi/ctrip/BizLoggingCustomizer.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...ollo/portal/spi/ctrip/WebContextConfiguration.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...lo/portal/spi/configuration/AuthConfiguration.java	6.09% <0%> (-0.32%)	1 <0> (ø)
...ork/apollo/biz/customize/BizLoggingCustomizer.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...rk/apollo/biz/eureka/ApolloEurekaClientConfig.java	66.66% <100%> (+16.66%)	2 <1> (ø)	⬇️
...ework/apollo/portal/controller/ItemController.java	7.14% <100%> (+5.62%)	1 <1> (ø)	⬇️
.../apollo/portal/listener/ConfigPublishListener.java	21.81% <100%> (+15.29%)	2 <1> (ø)	⬇️
... and 115 more

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[coveralls]

Coverage increased (+1.4%) to 53.573% when pulling 61819dc on kezhenxu94:style/use-constructor-injection into 5d15562 on ctripcorp:master.

[kezhenxu94]

There are some Field Injections left and some workarounds such as @Lazy annotation, but it needs refactoring if we want to replace them with Constructor Injection, and I'll do that if it's acceptable to you @nobodyiam , if any further changes should be done, please let me know. Thanks

[nobodyiam]

@kezhenxu94 Thanks!

I can see using constructor injection makes the program more robust and more friendly to tests. However, I'm curious about how did you manage to modify so many places, by hand or by some tool?

I also notice there are some places marked with @Lazy and some places not, is there any simple rule to distinguish the different usage?

[kezhenxu94]

I can see using constructor injection makes the program more robust and more friendly to tests. However, I'm curious about how did you manage to modify so many places, by hand or by some tool?

Modifying those places with modern IDE is a easy task, I'm using Intellij.

I also notice there are some places marked with @Lazy and some places not, is there any simple rule to distinguish the different usage?

The rule is that when the dependencies form a circle, i.e. A depends on B and B depends on A, then the dependencies must be annotated as @Lazy or exceptions will be thrown, this is considered a bad practice and need refactoring

[nobodyiam]

@kezhenxu94

Thanks for the explanation. Regarding the cyclic reference, how did you identify such case, manually or by some tool?

[kezhenxu94]

@kezhenxu94

Thanks for the explanation. Regarding the cyclic reference, how did you identify such case, manually or by some tool?

It's hard to identify that, though there are tools to detect that in this thread, I identified by running the test cases and Spring will print out the cyclic denpendencies graph.

[nobodyiam]

@kezhenxu94

Thanks! Will take a detailed look soon!

[nobodyiam]

LGTM