[Java] Incorrect enum generation for boolean-based data types

Description

Java code generator uses the wring jsonReader method in its read method when generating boolean-based enumerations.

Swagger-codegen version

3.0.33 and newer

Swagger declaration file content or url

Boolean1:
      description: True or False indicator
      type: boolean
      enum:
      - true
      - false

The resulting Java code looks as follows:

package some.package;

import java.util.Objects;
import java.util.Arrays;
import io.swagger.v3.oas.annotations.media.Schema;
import com.google.gson.annotations.SerializedName;
import java.io.IOException;
import com.google.gson.TypeAdapter;
import com.google.gson.annotations.JsonAdapter;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;

/**
 * True or False indicator
 */
@JsonAdapter(Boolean1.Adapter.class)
public enum Boolean1 {
  TRUE(true),
  FALSE(false);

  private Boolean value;

  Boolean1(Boolean value) {
    this.value = value;
  }

  public Boolean getValue() {
    return value;
  }

  @Override
  public String toString() {
    return String.valueOf(value);
  }

  public static Boolean1 fromValue(Boolean input) {
    for (Boolean1 b : Boolean1.values()) {
      if (b.value.equals(input)) {
        return b;
      }
    }
    return null;
  }

  public static class Adapter extends TypeAdapter<Boolean1> {
    @Override
    public void write(final JsonWriter jsonWriter, final Boolean1 enumeration) throws IOException {
      jsonWriter.value(String.valueOf(enumeration.getValue()));
    }

    @Override
    public Boolean1 read(final JsonReader jsonReader) throws IOException {
      Object value = jsonReader.nextString();
      return Boolean1.fromValue((Boolean)(value));
    }
  }
}

The malicious part is in the read method. The jsonReader tries to consume a string as next token, but the JSON contains boolean value in this case.

    @Override
    public Boolean1 read(final JsonReader jsonReader) throws IOException {
      Object value = jsonReader.nextString();
      return Boolean1.fromValue((Boolean)(value));
    }

{"dateTime":"2022-06-02T12:02:00.888000","endOfList":false}

As a consequence, any boolean value gets rejected with the following error message:

java.lang.IllegalStateException: Expected a string but was BOOLEAN at line 1 column 59 path $.endOfList

Correct consumer method for boolean-based values should be:

    @Override
    public Boolean1 read(final JsonReader jsonReader) throws IOException {
      Boolean value = jsonReader.nextBoolean();
      return Boolean1.fromValue((Boolean)(value));
    }
  }
}

Command line used for generation

Download Java-Code from SwaggerHub, under Export > Client SDK > Java, or using Swagger Code Generator (e.g., in the command-line or as Maven plugin).

Steps to reproduce

1. Create yaml specification with enum.
2. Generate Java Code, or download Java Code from SwaggerHub

Related issues/PRs

Suggest a fix/enhancement

After inspecting the mustache template used to generate the enumeration, the definition seems not to consider boolean-based values (cf. /src/main/resources/Java/modelEnum.mustache).

    @Override
    public {{#datatypeWithEnum}}{{{.}}}{{/datatypeWithEnum}}{{^datatypeWithEnum}}{{{classname}}}{{/datatypeWithEnum}} read(final JsonReader jsonReader) throws IOException {
      {{#isNumber}}BigDecimal value = new BigDecimal(jsonReader.nextDouble()){{/isNumber}}{{^isNumber}}{{#isInteger}}Integer value {{/isInteger}}{{^isInteger}}String value {{/isInteger}}= jsonReader.{{#isInteger}}nextInt(){{/isInteger}}{{^isInteger}}nextString(){{/isInteger}}{{/isNumber}};
      return {{#datatypeWithEnum}}{{{.}}}{{/datatypeWithEnum}}{{^datatypeWithEnum}}{{{classname}}}{{/datatypeWithEnum}}.fromValue({{#jackson}}value{{/jackson}}{{^jackson}}String.valueOf(value){{/jackson}});
    }

The suggested solution is to add a case for boolean values.

Start with src/main/resources/Java/modelEnum.mustache and reproduce the issue using the boolean enum specification shown in the report. Check the generated enum's Adapter.read method and verify generation and consumption of boolean values; done means the generated code accepts the boolean JSON token without the reported exception.