java - 尝试使用反射调用私有(private)字段上的方法时出现 NullPointerException

Question

原始问题描述How to run method on private field using reflection?

类(class)是

public class SecureResource {

    private HttpServletRequest request;
        public SecureResource() {}

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

基于@Jon 的回答

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

我做了以下事情

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");

我得到的request为null

并且字段 f 不为空

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

请告诉我我在哪里犯了错误？

Answer 1

代码是正确的，但谁说request不应该为null？向我们展示您的资源类的默认构造函数。 (注意:如果您依赖于某些注入(inject)的发生，则它不会发生。注入(inject)框架仅在您不规避它们时才起作用。)