[REQ][Java][Spring] Process and generate variables/objects (and their annotations) recursively in mustache

[DatApplePy]

Is your feature request related to a problem? Please describe.

Currently, all container objects (List, Set and Map) with their elements are processed as one in the generator (AbstractJavaCodegen). Example:

testList:
  type: array
  maxItems: 10
  items:
    type: array
    maxItems: 5
    uniqueItems: true
    items:
      type: string
      pattern: "^[0-9]{10,15}$"

datatypeWithEnum value of testList: List<@Size(max = 5) Set<@Pattern(regexp = "^[0-9]{10,15}$") String>>

Generated code:

@Size(max = 10)
private List<@Size(max = 5) Set<@Pattern(regexp = "^[0-9]{10,15}$") String>> testList;

This leads to 2 problems (that's all I've found so far): 1) Cannot create and apply custom annotations 2) Custom messages cannot be applied to Jakarta annotations

Describe the solution you'd like

It would be better if the dataTypeWithEnum value of the variables contained only the type of the current schema. Using the previous example, the result would be this:

name: testList
dataTypeWithEnum: List
isContainer: true
isArray: true
uniqueItems: false
...
items:
  dataTypeWithEnum: Set
  isContainer: true
  isArray: true
  uniqueItems: true
  ...
  items:
    dataTypeWithEnum: String

This way we can generate these structures recursively and also apply custom annotation and more.

Additional context

Since this issue is the extended form of another issue (#19557), I am already working on the feature. I planned to implement the feature in two stages: 1) Refactor mustache templates related to this issue

• pojo
• beanValidation
• beanValidationCore
• nullableDataType
• nullableDataTypeBeanValidation 2) Redesign AbstractJavaCodegen, e.g. getTypeDeclaration, getTypeDeclarationForArray, getBeanValidation, etc... I've already done some research and, for example, the ones listed above may change, or they are not needed.

Note: The development process can be slow because I read a lot of documentation (and StackOverFlow) and experiment a lot to make everything work as intended.

[DatApplePy]

First stage: https://github.com/OpenAPITools/openapi-generator/compare/master...DatApplePy:openapi-generator:fix_issue_19601