[Java] option for the prefix of boolean getters

[jmini]

PR checklist

• 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\.
• Filed the PR against the correct branch: master, 3.1.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.
  Java: @bbdouglas (2017/07) @JFCote (2017/08) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01)

Description of the PR

This PR adds a new option to all java generators (java client, jaxrs server, spring, …): booleanGetterPrefix

This new option influence the name of the getter generated for a boolean property in a model.

Example values for booleanGetterPrefix:

• is: default value in 3.0.x.
• get: new default value starting with 3.1.0

With following OAS3 (extract):

components:
  schemas:
  schemas:
    Order:
      type: object
      properties:
        id:
          type: integer
          format: int64
        status:
          type: string
          enum:
            - placed
            - approved
            - delivered
        complete:
          type: boolean

Generated code with is value:

  public Boolean isComplete() {
    return complete;
  }

With get value:

  public Boolean getComplete() {
    return complete;
  }

This was also discussed in:

• [Java] Bug: boolean getter used for non-primitive Boolean swagger-api/swagger-codegen#7261
• Wrong getter for Boolean Object swagger-api/swagger-codegen#7764
• Add CLI option to customize the Boolean getter swagger-api/swagger-codegen#7638
• ...

[cbornet]

If this PR is for 3.1.0, I suggest making the change to get as default now

[jmini]

@cbornet: yes current change is as minimal as possible (no impact on the generated code).
Modifying the default value can be made in a follow up PR.

[jmini]

I have pushed some more commits to change the default value.

I also think that it is important for our users to have a short list of the breaking changes in a major/minor release.

I have started docs/migration-guide.adoc to list all breaking changes of a release.

[jmini]

@macjohnny and @cbornet (you were both interested by the feature in a previous conversation), any additional feedback on this?

I would like to merge this, but until now nobody gave it a try.

[wing328]

Did a test locally and work as expected.

[macjohnny]

looks good, although I haven't tested it

[jmini]

Input @cbornet:

We need the getXXX() getter because of the Java Beans spec : http://www.oracle.com/technetwork/articles/javaee/spec-136004.html
isXXX() is for boolean, not for Boolean

[cbornet]

At paragraph 8.3 😄

[alex-spicer]

Does this apply to other languages too? Or is this just java? jaxrs-jersey I still see isX getter.
Any forced flag to help here?

[wing328]

The enhancement is made to the abstract java codegen class, which should cover all java generators.

Maybe the mustache template needs to be updated. Welcome PR to plot the enhancement form Java client mustache/generator to JAX-RS templates/generators.