I want to add a custom attribute to the start of my xml tag using java, tried using serializer & other solutions but did not work.

 *Code* :
    
    @Data
    @Builder
    @NoArgsConstructor
    @AllArgsConstructor
    @JsonIgnoreProperties(ignoreUnknown = true)
    @JacksonXmlRootElement(localName = "TestClass")
    public class TestClass{
    
    
     @JacksonXmlProperty(localName = "TestVariable")
      private String testVariable;
    
    }
    

I am expecting the below output where i have mentioned custom attribute in the start tag:

    <TestClass>
      <TestVariable unit="km">100</TestVariable>
    </TestClass>
    
    custom attribute : unit="km"