Tries to fix #18975 by changing how the deserializer interacts with its parent class (#18976)

* [JAVA] Fix for #18975, ensure static block of parent deser class loads

* Add sample spec with type with anyOf

modules/openapi-generator/src/main/resources/Java/libraries/jersey2/anyof_model.mustache

@@ -57,7 +57,7 @@ public class {{classname}} extends AbstractOpenApiSchema{{#vendorExtensions.x-im
 
             Object deserialized = null;
             {{#discriminator}}
-            Class<?> cls = JSON.getClassForElement(tree, {{classname}}.class);
+            Class<?> cls = JSON.getClassForElement(tree, new {{classname}}().getClass());
             if (cls != null) {
                 // When the OAS schema includes a discriminator, use the discriminator value to
                 // discriminate the anyOf schemas.

modules/openapi-generator/src/main/resources/Java/libraries/jersey3/anyof_model.mustache

@@ -57,7 +57,7 @@ public class {{classname}} extends AbstractOpenApiSchema{{#vendorExtensions.x-im
 
             Object deserialized = null;
             {{#discriminator}}
-            Class<?> cls = JSON.getClassForElement(tree, {{classname}}.class);
+            Class<?> cls = JSON.getClassForElement(tree, new {{classname}}().getClass());
             if (cls != null) {
                 // When the OAS schema includes a discriminator, use the discriminator value to
                 // discriminate the anyOf schemas.

modules/openapi-generator/src/main/resources/Java/libraries/native/anyof_model.mustache

@@ -54,7 +54,7 @@ public class {{classname}} extends AbstractOpenApiSchema{{#vendorExtensions.x-im
 
             Object deserialized = null;
             {{#discriminator}}
-            Class<?> cls = JSON.getClassForElement(tree, {{classname}}.class);
+            Class<?> cls = JSON.getClassForElement(tree, new {{classname}}().getClass());
             if (cls != null) {
                 // When the OAS schema includes a discriminator, use the discriminator value to
                 // discriminate the anyOf schemas.

modules/openapi-generator/src/test/resources/bugs/issue_18975.yaml

@@ -0,0 +1,47 @@
+openapi: 3.0.1
+info:
+  title: sample issue 18975
+  description: sample issue 18975
+  version: "1.0"
+paths:
+  /sample:
+    get:
+      summary: sample
+      operationId: getSample
+      responses:
+        "200":
+          description: Found vehicle.
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/DifficultType'
+components:
+  schemas:
+    SubA:
+      required:
+        - type
+      type: object
+      properties:
+        type:
+          type: string
+        sim:
+          type: string
+    SubB:
+      required:
+        - type
+      type: object
+      properties:
+        type:
+          type: string
+        system:
+          type: string
+    DifficultType:
+      type: object
+      discriminator:
+        propertyName: type
+        mapping:
+          "typeA": '#/components/schemas/SubA'
+          "typeB": '#/components/schemas/SubB'
+      anyOf:
+        - $ref: '#/components/schemas/SubA'
+        - $ref: '#/components/schemas/SubB'