java - (Java)if 语句优化

Question

需要优化这段代码:

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 提示这种方法的复杂性。

更改起来不是那么容易，因为我们需要在获取其值之前检查注解类型!

注意:陷阱位于没有 value() 方法的 Annotation 接口(interface)上。

附言: 此代码基于此 example (代码示例 4)

Answer 1

如果反射是一个选项，你总是可以做类似的事情

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);
    }
}