Add internal java17 additionalProperty setting

Author: Mattias-Sehlstedt

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java

@@ -109,7 +109,6 @@ public class JavaClientCodegen extends AbstractJavaCodegen
     // Internal configurations
     public static final String SINGLE_REQUEST_PARAMETER = "singleRequestParameter";
     public static final String STATIC_REQUEST = "staticRequest";
-    // TODO attempt to implement the setting similar to how it is done here https://github.com/OpenAPITools/openapi-generator/pull/20590/files
     public static final String JAVA_17 = "java17";
 
     public static final String SERIALIZATION_LIBRARY_GSON = "gson";
@@ -380,6 +379,10 @@ public void processOpts() {
         writePropertyBack(SINGLE_REQUEST_PARAMETER, getSingleRequestParameter());
         writePropertyBack(STATIC_REQUEST, getStaticRequest());
 
+        if (libWebClient && (useSealedOneOfInterfaces || useJakartaEe)) {
+            writePropertyBack(JAVA_17, true);
+        }
+
         if (!useRxJava && !useRxJava2 && !useRxJava3) {
             additionalProperties.put(DO_NOT_USE_RX, true);
         }

samples/client/petstore/java/webclient-sealedInterface/gradlew

@@ -38,8 +38,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.13.0</version>
                 <configuration>
-                    <source>1.8</source>
-                    <target>1.8</target>
+                    <source>17</source>
+                    <target>17</target>
                 </configuration>
             </plugin>
             <plugin>