Return custom code and message from AWS Lambda with Java

Question

I have this test code:

package process;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestBody;
import process.dto.Request;

@SpringBootApplication
public class FunctionConfiguration {

    /*
     * You need this main method (empty) or explicit <start-class>example.FunctionConfiguration</start-class>
     * in the POM to ensure boot plug-in makes the correct entry
     */
    public static void main(String[] args) {
        // empty unless using Custom runtime at which point it should include
        // SpringApplication.run(FunctionConfiguration.class, args);
    }

    public String process(@RequestBody Request request)
    {
        // Do some processing. Return HTTP 200 if OK or return custom error code 500 with error message

        return "Hello, World " + request.getEmail();
    }
}

I don't use AWS API Gateway. I make a direct API requests. How I can return a custom http code and message? Standard Response entity is not working.