(Java) if operator optimization

Question

You need to optimize this code:

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import javax.ws.rs.CookieParam;
import javax.ws.rs.FormParam;
import javax.ws.rs.HeaderParam;
import javax.ws.rs.MatrixParam;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.QueryParam;
...

private String valueParam(Annotation a) {

    String value = "";

    if (a.annotationType() == QueryParam.class) {
        value = ((QueryParam) a).value();
    } else if (a.annotationType() == PathParam.class) {
        value = ((PathParam) a).value();
    } else if (a.annotationType() == CookieParam.class) {
        value = ((CookieParam) a).value();
    } else if (a.annotationType() == HeaderParam.class) {
            value = ((HeaderParam) a).value();
    } else if (a.annotationType() == MatrixParam.class) {
            value = ((MatrixParam) a).value();
    } else if (a.annotationType() == FormParam.class) {
            value = ((FormParam) a).value();
    }

    return value;
 }

SonarQube complains about the complexity of this method.

It is not so easy to change, because we need to check the type of annotation before getting its value!

Note. The trap is in the Annotation interface, which does not have a value () method.

PS: This code is based on this example (code example 4)

Answer 1

If reflection is an option, you can always do something like

public class Test {

    @PathParam("path")
    public Response doSomething() {
        return null;
    }

    public static void main(String[] args) throws Exception {
        Method method = Test.class.getMethod("doSomething");
        Annotation annotation = method.getAnnotations()[0];
        System.out.println(getValue(annotation));
    }

    private static String getValue(Annotation annotation) throws Exception {
        Class<?> type = annotation.annotationType();
        if (!ANNOTATIONS.contains(type)) {
            throw new IllegalArgumentException("...");
        }
        String value = (String) type.getMethod("value").invoke(annotation);
        return value;
    }

    private static final Set<Class<?>> ANNOTATIONS;

    static {
        Set<Class<?>> annotations = new HashSet<>();
        annotations.add(HeaderParam.class);
        annotations.add(QueryParam.class);
        annotations.add(PathParam.class);
        annotations.add(MatrixParam.class);
        annotations.add(CookieParam.class);
        annotations.add(FormParam.class);
        ANNOTATIONS = Collections.unmodifiableSet(annotations);
    }
}