[AndreyVMarkelov]

Fixes #25065

What does this PR do?

Fixes Java okhttp-gson validation for string properties that use not with an enum.

For a schema such as:

kind:
  type: string
  not:
    enum:
      - known

the generated validateJsonElement method previously checked only that kind was a string and did not enforce the value excluded by not.

This caused oneOf schemas that rely on not: enum to become ambiguous. For example, {"kind":"known"} could incorrectly match both the schema that explicitly allows "known" and the schema that excludes it.

Implementation

• Reads string enum values from the property's composedSchemas.not metadata during Java client model-property post-processing.
• Exposes those excluded values to the okhttp-gson POJO template.
• Generates validation that rejects matching excluded string values.
• Keeps the change intentionally scoped to Java okhttp-gson and string enums under not.

Tests

Added an OpenAPI 3.1 regression fixture with:

• Known.kind: enum: [known]
• Other.kind: not: { enum: [known] }
• Union: oneOf: [Known, Other]

Added a Java client generation test that verifies the generated Other validation:

• checks the actual kind property;
• rejects "known";
• does not incorrectly validate a synthetic not_schema property.

Targeted test:

JavaClientCodegenTest#testOneOfNotEnumValidation

passes successfully.

---

Summary by cubic

Fixes Java okhttp-gson validation so string properties using not with an enum reject excluded values, resolving ambiguity in oneOf schemas that rely on not: enum (issue #25065).

Previously validateJsonElement only checked that the property was a string, so {"kind":"known"} could match both a schema allowing "known" and one excluding it. The generator now reads the excluded values from composedSchemas.not, exposes them via a vendor extension, and generates validation that throws an IllegalArgumentException for disallowed values.

The change is scoped to Java okhttp-gson string enums under not, and adds a regression fixture plus a generation test covering the oneOf scenario, including enum references.

^{Written for commit fd764ca. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 4 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[AndreyVMarkelov]

@KannaKim @martin-mfg would you mind taking a look when you have a chance? This is a small Java client bug fix with regression coverage and green CI.

This issue currently blocks our work on a new Dropbox SDK generated with OpenAPI Generator, so getting it into the next release would be very helpful. Thanks!

[wing328]

thanks for the PR

cc @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @martin-mfg (2023/08) @KannaKim (2026/07)

[wing328]

tested and the change compiles without issues, e.g.

-@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", date = "2026-10-05T16:16:20.930519800+08:00[Asia/Hong_Kong]", comments = "Generator version: 7.26.0-SNAPSHOT")
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", date = "2026-10-05T16:18:30.360073600+08:00[Asia/Hong_Kong]", comments = "Generator version: 7.26.0-SNAPSHOT")
 public class Other {
   public static final String SERIALIZED_NAME_KIND = "kind";
   @SerializedName(SERIALIZED_NAME_KIND)
@@ -153,6 +153,16 @@ public class Other {
         }
       }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
+      if (jsonObj.get("kind") != null
+              && !jsonObj.get("kind").isJsonNull()
+              && jsonObj.get("kind").isJsonPrimitive()
+              && jsonObj.get("kind").getAsJsonPrimitive().isString()
+              && "known".equals(jsonObj.get("kind").getAsString())) {
+        throw new IllegalArgumentException(String.format(
+            java.util.Locale.ROOT,
+            "The field `kind` in the JSON string matches a value disallowed by `not`: `%s`",
+            jsonObj.get("kind").toString()));
+      }

but the indentation seems missing 2 spaces. will file a follow up PR to fix it.

UPDATE: merged #25122 to fix the indentation.