Do not apply content-type header if no request body

[bmordue]

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• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

The intent is to avoid adding a Content-Type header on requests made by a generated Java-feign client if the request body is empty. This is to fix #6647

• Do not set contentType for requests that have no body params specified.
• In the Java-Feign template, avoid adding an empty @Headers annotation for "Content-Type" if contentType is not set.

[wing328]

@bmordue shall we keep the logic path.getGet() != null || ! operation.equals(path.getGet()) ?

For POST using HTTP form (not JSON/XML string), we also need the content-type right?

[bmordue]

Thanks, I've made sure the default content-type for form data gets applied too.

I don't think the original logic was correct: any path that includes a GET operation would have a default content-type applied, which doesn't seem right. I've added some tests that demonstrate this (ac79987).

[wing328]

Please run ./bin/java-petstore-all.sh to update Java Petstore client so that CIs can verify the result.

[bmordue]

Apologies for my slow reply, I've been travelling. I ran the update script and committed the changes.

[wing328]

cc @bbdouglas @JFCote @sreeshas @jfiala @lukoyanov @cbornet

[JFCote]

@wing328 Is it normal that this generator use "gson" ? AFAIK, most if not all generator here use jackson?
If that is ok, it looks good to me but I don't know Feign at all :)

[wing328]

cc @davidgri for review as well since the previous if-condition has been revised.

[wing328]

@JFCote Java Feign client uses jackson:

    <!-- JSON processing: jackson -->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>${jackson-version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
      <version>${jackson-version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>${jackson-version}</version>
    </dependency>
    <dependency>
      <groupId>com.github.joschi.jackson</groupId>
      <artifactId>jackson-datatype-threetenbp</artifactId>
      <version>${jackson-threetenbp-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.oltu.oauth2</groupId>
      <artifactId>org.apache.oltu.oauth2.client</artifactId>
      <version>${oltu-version}</version>
    </dependency>

[JFCote]

@wing328 I'm talking about this. You can see use of Gson in other modifier files too.

[cbornet]

The retrofit generator does use gson. I guess this change is due to regenerating all the Java samples.

[JFCote]

ok no problem then. :)

[wing328]

If no further question or feedback on this, I'll merge it on coming Monday/Tuesday.