[BUG] maven plugin generating java classes with non standard annotations

Description

The current Java classes generated by the plugin exhibit a few notable issues:

1. Non-standard annotations such as @javax.annotation.Nonnull or @javax.annotation.Nullable from com.google.code.findbugs:jsr305:3.0.2 are utilised.

2. Annotations are placed at the method level instead of the recommended field level.

openapi-generator version

7.5.0

generatorName: java

OpenAPI declaration file content or url

{
  "openapi": "3.1.0",
  "info": {
    "title": "Sample contract",
    "version": "1.0.0"
  },
  "paths": {},
  "components": {
    "schemas": {
      "Request": {
        "type": "object",
        "required": ["token"],
        "properties": {
          "token": {
            "type": "string"
          }
        }
      }
    }
  }
}

Generation Details

Generated java class

/*
 * Sample contract
 * No description provided (generated by Openapi Generator https://github.com/openapitools/openapi-generator)
 *
 * The version of the OpenAPI document: 1.0.0
 * 
 *
 * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
 * https://openapi-generator.tech
 * Do not edit the class manually.
 */


package com.sample;

import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.util.StringJoiner;
import java.util.Objects;
import java.util.Map;
import java.util.HashMap;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonTypeName;
import com.fasterxml.jackson.annotation.JsonValue;
import java.util.Arrays;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;


/**
 * Request
 */
@JsonPropertyOrder({
  Request.JSON_PROPERTY_TOKEN
})
@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", date = "2024-04-22T17:39:48.544568+02:00[Europe/Madrid]", comments = "Generator version: 7.5.0")
public class Request {
  public static final String JSON_PROPERTY_TOKEN = "token";
  private String token;

  public Request() { 
  }

  public Request token(String token) {
    this.token = token;
    return this;
  }

   /**
   * Get token
   * @return token
  **/
  @javax.annotation.Nonnull
  @JsonProperty(JSON_PROPERTY_TOKEN)
  @JsonInclude(value = JsonInclude.Include.ALWAYS)

  public String getToken() {
    return token;
  }


  @JsonProperty(JSON_PROPERTY_TOKEN)
  @JsonInclude(value = JsonInclude.Include.ALWAYS)
  public void setToken(String token) {
    this.token = token;
  }


  /**
   * Return true if this Request object is equal to o.
   */
  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    Request request = (Request) o;
    return Objects.equals(this.token, request.token);
  }

  @Override
  public int hashCode() {
    return Objects.hash(token);
  }

  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("class Request {\n");
    sb.append("    token: ").append(toIndentedString(token)).append("\n");
    sb.append("}");
    return sb.toString();
  }

  /**
   * Convert the given object to string with each line indented by 4 spaces
   * (except the first line).
   */
  private String toIndentedString(Object o) {
    if (o == null) {
      return "null";
    }
    return o.toString().replace("\n", "\n    ");
  }

  /**
   * Convert the instance into URL query string.
   *
   * @return URL query string
   */
  public String toUrlQueryString() {
    return toUrlQueryString(null);
  }

  /**
   * Convert the instance into URL query string.
   *
   * @param prefix prefix of the query string
   * @return URL query string
   */
  public String toUrlQueryString(String prefix) {
    String suffix = "";
    String containerSuffix = "";
    String containerPrefix = "";
    if (prefix == null) {
      // style=form, explode=true, e.g. /pet?name=cat&type=manx
      prefix = "";
    } else {
      // deepObject style e.g. /pet?id[name]=cat&id[type]=manx
      prefix = prefix + "[";
      suffix = "]";
      containerSuffix = "]";
      containerPrefix = "[";
    }

    StringJoiner joiner = new StringJoiner("&");

    // add `token` to the URL query string
    if (getToken() != null) {
      joiner.add(String.format("%stoken%s=%s", prefix, suffix, URLEncoder.encode(String.valueOf(getToken()), StandardCharsets.UTF_8).replaceAll("\\+", "%20")));
    }

    return joiner.toString();
  }
}

Steps to reproduce

1. Use OpenApi spec provided
2. Generate java class (POJO)

Expected behaviour

To rectify these issues, the ideal Java class generation should adhere to the following specifications:

1. Use standard annotations like @javax.validation.constraints.NotNull
2. Place annotations at the field level.

The expected behaviour can be summarised as follows:

package com.sample;

import javax.annotation.processing.Generated;
import javax.validation.constraints.NotNull;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;


/**
 * Request
 * <p>
 * 
 * 
 */
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
    "token"
})
public class Request {

    /**
     * 
     * (Required)
     * 
     */
    @JsonProperty("token")
    @NotNull
    private String token;

    /**
     * 
     * (Required)
     * 
     */
    @JsonProperty("token")
    public String getToken() {
        return token;
    }

    /**
     * 
     * (Required)
     * 
     */
    @JsonProperty("token")
    public void setToken(String token) {
        this.token = token;
    }

    public Request withToken(String token) {
        this.token = token;
        return this;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(Request.class.getName()).append('@').append(Integer.toHexString(System.identityHashCode(this))).append('[');
        sb.append("token");
        sb.append('=');
        sb.append(((this.token == null)?"<null>":this.token));
        sb.append(',');
        if (sb.charAt((sb.length()- 1)) == ',') {
            sb.setCharAt((sb.length()- 1), ']');
        } else {
            sb.append(']');
        }
        return sb.toString();
    }

    @Override
    public int hashCode() {
        int result = 1;
        result = ((result* 31)+((this.token == null)? 0 :this.token.hashCode()));
        return result;
    }

    @Override
    public boolean equals(Object other) {
        if (other == this) {
            return true;
        }
        if ((other instanceof Request) == false) {
            return false;
        }
        Request rhs = ((Request) other);
        return ((this.token == rhs.token)||((this.token!= null)&&this.token.equals(rhs.token)));
    }

}

This revised code adheres to the standard annotations and correctly places them at the field level, as requested.

Start with the Java generator's POJO output for the provided OpenAPI declaration and compare the generated Request class with the expected example. Confirm that required fields use standard validation annotations and that those annotations are placed on fields, then rerun the two generation steps to verify the output.