尝试使用Reflection在私有字段上调用方法时出现NullPointerException

Question

The original issue is described How to run method on private field using reflection?

The class is

public class SecureResource {

    private HttpServletRequest request;
        public SecureResource() {}

    @Inject
    public SecureResource(@Nonnull final HttpServletRequest request) {
        this.request = request;
    }
    // more things
}

Based on @Jon answer

(Where resource is a reference to the relevant instance of SecureResource.)

I did the following

Class cls = response.getResourceClass();
Object obj = cls.newInstance();
Field f = cls.getDeclaredField("request");
f.setAccessible(true);
HttpServletRequest request = (HttpServletRequest) f.get(obj);
String auth = request.getHeader("X-AUTH");

and I get request as null

and the Field f is not null

private javax.servlet.http.HttpServletRequest com.sunrunhome.blackbird.service.SecureResource.request

Please let me know where I am making mistakes here?

Answer 1

The code is correct as written, but who says that request isn't supposed to be null ? Show us the default constructor of your resource class. (Note: if you're relying on some injection to happen, it won't. Injection frameworks only work when you don't circumvent them.)