Add HttpRequestBuilder

[tumile]

Motivation:

• Provide a fluent way of building HttpRequest. We already have many factory methods, but setting custom headers, query/path params is not very straightforward.
• Issues Improve the usability of WebClient #2390, Provide a fluent way to build http client request. #2148. We want a friendlier API with more functionalities.
• Gather more comments and thoughts on how the API should look like.

Modifications:

• Add HttpRequest.builder() for fluent construction of HttpRequest
• Add WebClient.prepare() for fluent construction and execution of HttpRequest

Result:

WebClient client = ...;

// Creates a POST HttpRequest to "/foo?q=bar" 
// with headers "cookie: name=value" and "authorization: value" and a JSON body.
// Using HttpRequest.builder():
client.execute(
    HttpRequest.builder()
               .post("/{resource}")
               .pathParam("resource", "foo")
               .queryParam("q", "bar")
               .cookie(Cookie.of("name", "value"))
               .header("authorization", "value")
               .content(MediaType.JSON, "{\"foo\":\"bar\"}"));

// Using WebClient.prepare():
client.prepare()
      .post("/{resource}")
      .pathParam("resource", "foo")
      .queryParam("q", "bar")
      .cookie(Cookie.of("name", "value"))
      .header("authorization", "value")
      .content(MediaType.JSON, "{\"foo\":\"bar\"}")
      .execute();

[codecov]

Codecov Report

Merging #3110 (ba35648) into master (454a22c) will increase coverage by 0.14%.
The diff coverage is 78.88%.

@@             Coverage Diff              @@
##             master    #3110      +/-   ##
============================================
+ Coverage     73.90%   74.04%   +0.14%     
- Complexity    12305    12711     +406     
============================================
  Files          1064     1104      +40     
  Lines         46844    48208    +1364     
  Branches       5949     6125     +176     
============================================
+ Hits          34619    35697    +1078     
- Misses         9201     9378     +177     
- Partials       3024     3133     +109     

Impacted Files	Coverage Δ	Complexity Δ
...rp/armeria/client/WebClientRequestPreparation.java	27.58% <27.58%> (ø)	6.00 <6.00> (?)
...orp/armeria/common/AbstractHttpRequestBuilder.java	86.88% <86.88%> (ø)	47.00 <47.00> (?)
...om/linecorp/armeria/common/HttpRequestBuilder.java	96.29% <96.29%> (ø)	26.00 <26.00> (?)
...in/java/com/linecorp/armeria/client/WebClient.java	68.88% <100.00%> (+0.70%)	23.00 <1.00> (+1.00)
.../java/com/linecorp/armeria/common/HttpRequest.java	80.64% <100.00%> (+2.38%)	31.00 <1.00> (+2.00)
.../com/linecorp/armeria/server/grpc/GrpcService.java	28.57% <0.00%> (-71.43%)	2.00% <0.00%> (ø%)
...c/main/java/com/linecorp/armeria/server/Route.java	66.66% <0.00%> (-33.34%)	2.00% <0.00%> (ø%)
...linecorp/armeria/common/DefaultRequestHeaders.java	70.58% <0.00%> (-11.77%)	9.00% <0.00%> (-1.00%)
...a/com/linecorp/armeria/server/CompositeRouter.java	46.87% <0.00%> (-9.38%)	6.00% <0.00%> (-1.00%)
...ria/server/metric/PrometheusExpositionService.java	81.25% <0.00%> (-8.75%)	6.00% <0.00%> (+3.00%)	⬇️
... and 185 more

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[trustin]

Thank you so much for volunteering on this issue. This is gonna be a great addition to Armeria API!

[tumile]

Somehow AppVeyor sometimes just hangs on a test and times out/doesn't run at all.
https://ci.appveyor.com/project/line/armeria/builds/35808547/job/82961887f2xb9vxw
https://ci.appveyor.com/project/line/armeria/builds/35809237/job/5myrrqwtokx8k9ag

[ikhoon]

Somehow AppVeyor sometimes just hangs on a test and times out/doesn't run at all.
ci.appveyor.com/project/line/armeria/builds/35808547/job/82961887f2xb9vxw
ci.appveyor.com/project/line/armeria/builds/35809237/job/5myrrqwtokx8k9ag

Hmm, let me rerun it.

[trustin]

Mostly minor ones. 👍

[trustin]

Excellent job, @tumile. This is a great usability improvement in Armeria's HTTP client. 🙇 Just a few nits

[trustin]

Excellent work! I'm getting really curious about what your next improvement will be 💡

[ikhoon]

Thanks! @tumile 🙇‍♂️
Left a minor comment.

[minwoox]

Excellent work! 👍

[trustin]

🎉🎉🎉

[tumile]

Thanks for reviewing 🙇 !