[BUG][JAVA] "ID" in class names altered to "Id"

Description

The behaviour leads to compile errors because of the file name / class name mismatch. The issue unveiled when trying to generate the code for the jira rest client.

openapi-generator version

5.0.1 (openapi-generator-maven-plugin)

OpenAPI declaration file content or url

Below the execution configuration of the maven plugin:

<execution>
    <goals>
        <goal>generate</goal>
    </goals>
    <configuration>
        <inputSpec>https://developer.atlassian.com/cloud/jira/platform/swagger-v3.v3.json</inputSpec>
        <generatorName>java</generatorName>
        <library>resttemplate</library>
        <apiPackage>com.atlassian.jira.rest.client.api</apiPackage>
        <modelPackage>com.atlassian.jira.rest.client.model</modelPackage>
        <invokerPackage>com.atlassian.jira.rest.client</invokerPackage>
        <groupId>com.atlassian.jira.rest</groupId>
        <artifactId>client</artifactId>
        <configOptions>
            <dateLibrary>java8</dateLibrary>
        </configOptions>
    </configuration>
</execution>

Command line used for generation

See execution definition above.

Steps to reproduce

Add above execution definiton to any maven java project using openapi-generator. Run commands maven clean, maven install.

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/3428
https://github.com/OpenAPITools/openapi-generator/issues/1692

Suggest a fix/enhancement

Define separate rule to handle the (sub)string "ID". Classes must not be renamed.

Start by reproducing the Maven plugin execution with the supplied Jira OpenAPI URL and Java generator configuration, then trace the Java model/class naming entry point. Confirm which generated class names containing "ID" are changed to "Id" and compare them with their file names. Done means the generated Java classes and files preserve the intended "ID" spelling and compile successfully.