public class Payload {
    @NotNull(message = "amount is mandatory")
    private BigDecimal amount;

    @NotNull(message = "currency is mandatory")
    private String currency;
    
    // setter & getter & constructors ...

}

@JsonRpcService("/generate")
public interface IGenerator {
    String generate(@Valid @JsonRpcParam(value = "payload") Payload payload);
}

@AutoJsonRpcServiceImpl
@Component
public class GeneratorImpl implements IGenerator {
    @Override
    public String generate(@Valid @JsonRpcParam(value = "payload") Payload payload) {
         return payload.getAmount() +" "+ payload.getCurrency();
    }
}