minor improvements on java client based on intellji ide (#13864)

samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/ServerConfiguration.java

@@ -42,7 +42,7 @@ public class ServerConfiguration {
                     throw new IllegalArgumentException("The variable " + name + " in the server URL has invalid value " + value + ".");
                 }
             }
-            url = url.replaceAll("\\{" + name + "\\}", value);
+            url = url.replace("{" + name + "}", value);
         }
         return url;
     }