[JAVA] Support Javax injection for creation of API delegate instead of static factory pattern

[JLLeitschuh]

Description

Replace/Complement static factory with DI injection

Currently, the generator for jersey and rest-easy use the static factory pattern to create the delegate that gets called by the REST API.

Swagger-codegen version

Whatever version this gradle plugin in using, (I think it's the current release).

Swagger declaration file content or url

Use the pet-store as an example.

Command line used for generation

swagger {
    inputSpec = "${project.projectDir.path}/spec/swagger.yaml"

    output = 'build/swagger'
    language = 'jaxrs-resteasy'

    additionalProperties = [
            'invokerPackage'   : 'edu.wpi.grip.web.swagger',
            'modelPackage'     : 'edu.wpi.grip.web.swagger.model',
            'apiPackage'       : 'edu.wpi.grip.web.swagger.api',
            'serializableModel': 'true'
    ]

    apis = ''
    models = ''
    supportingFiles = ''
}

Suggest a Fix

I'm using a custom api.mustache file that replaces the delegate creation with constructor injection.

import javax.inject.Inject;

public class {{classname}}  {
    private final {{classname}}Service delegate;

    @Inject
    {{classname}}({{classname}}Service delegate) {
        this.delegate = delegate;
    }

If a zero argument constructor is needed for other reasons and other frameworks both solutions could be implemented in parallel.

import javax.inject.Inject;

public class {{classname}}  {
    private final {{classname}}Service delegate;

    {{classname}}() { // Zero argument constructor because some frameworks need this
        this({{classname}}ServiceFactory.get{{classname}}(););
    }

    @Inject
    {{classname}}({{classname}}Service delegate) {
        this.delegate = delegate;
    }

[JLLeitschuh]

Is this something that would be pull request worthy?
Would this be too much of a breaking change because it would create a direct dependency upon javax.inject annotations?

This could also be done without the injection as you can use DI frameworks to bind to constructors.
Example: https://github.com/google/guice/wiki/ToConstructorBindings

[willgorman]

I'd definitely like to have something like this too. Modifying the generated API class to add DI after the fact means giving up the ability to easily regenerate when the API spec is updated.

[JLLeitschuh]

If you are looking for my version of the template with dependency injection it can be found here.
CustomRestEasyTemplates.zip

[wing328]

@JLLeitschuh please kindly submit a PR so that we can review the enhancement.

[karnik]

Hi, I've also overwritten the templates to replace the static factory with DI. Since this could break something when CDI (JSF 299) is missing the introduction of a new language might be a good solution?

jaxrs-resteasy-cdi for example.

[JLLeitschuh]

I did something similar with Spring in such a way that it shouldn't break anything:
#4439

[karnik]

OK, adding a parameter should also work.

[mamghari]

@JLLeitschuh @wing328 we should be careful when using DI because it mainly depends on the DI framework you would like to use : Spring ? Guice ? HK2 ? etc...
So the swagger code generator should generate generic code and should be linked to any kind of Implementation framework. Using javax.inject is nice because it is the specification, then it leads to developers to choose the right implementation framework to use.

[JLLeitschuh]

I agree with using javax.inject I use javax.inject myself. The thing is, the code generator is generating code for specific frameworks. The spring generator is generating for spring. There are other generators generating for other frameworks. I don't know if you can decouple that well.