[BUG][JAVA][Gradle Plugin] Java client generator not initializing fields

[saurabhsjoshi]

Bug Report Checklist

• [x] Have you provided a full/minimal spec to reproduce the issue?
• [x] Have you validated the input using an OpenAPI validator (example)?
• [x] What's the version of OpenAPI Generator used?
• [x] Have you search for related issues/PRs?
• [x] What's the actual output vs expected output?
• [ ] [Optional] Bounty to sponsor the fix (example)

Description

Using the openapi-generator gradle plugin I setup a task to generate code for the Petstore example YAML. Checking the generated Java classes I can see this in Pet.java:

 @JsonProperty("id")
  private Long id = ;

  @JsonProperty("name")
  private String name = ;

  @JsonProperty("tag")
  private String tag = ;

My Gradle task:

task generatePetStore(type: org.openapitools.generator.gradle.plugin.tasks.GenerateTask) {
    String basePackage = "com.example.petstore"
    verbose = true
    library = "resttemplate"
    generatorName = "java"
    inputSpec = "${project.rootDir}/swagger/petstore.yaml".toString()
    outputDir = "${project.buildDir}/generated/api/petstore"
    invokerPackage = basePackage
    apiPackage = basePackage + ".controller"
    modelPackage = basePackage + ".model"
    configOptions = [
            dateLibrary: "java8-localdatetime"
    ]
}

openapi-generator version

openapi-generator-gradle-plugin 4.2.2

OpenAPI declaration file content or url

URL: https://github.com/OAI/OpenAPI-Specification/blob/master/examples/v3.0/petstore.yaml

Command line used for generation

Steps to reproduce

1. Download Petstore Example YAML
2. Run code generation using the Gradle Plugin
3. Navigate to the Pet.java generated file

Related issues/PRs

Suggest a fix

The fields probably need to be initialized to null at least as the generated code is invalid Java syntax. Something like

  @JsonProperty("id")
  private Long id = null;

  @JsonProperty("name")
  private String name = null;

  @JsonProperty("tag")
  private String tag = null;

[saurabhsjoshi]

I seem to have narrowed down the issue. It appears that if you have the swagger-codegen plugin in your class path (specifically I had io.swagger:swagger-codegen:2.3.1) it results in the above error. Removing this plugin resolved the issue. Not sure if having a different plugin in the classpath should affect the functioning of this plugin so keeping the bug open.

Here is my original build.gradle configuration:

buildscript {
...
 dependencies {
        classpath("io.swagger:swagger-codegen:2.3.1")
        classpath "org.openapitools:openapi-generator-gradle-plugin:4.2.2"
    }
}

Removing the swagger-codegen solved the issue

[AledLewis]

Saurabh, you saved my day! Hitting the exact same issue and same resolution.