无法从tomcat中的自定义类加载器加载的类中获取注释

Question

给定班级 org.popper.example.pages.Login

@Page(name="Login")
public interface Login {
}

导出到c:\pos\example.jar以下servlet

public class PopperServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public static void main(String[] args) throws MalformedURLException, ClassNotFoundException {
        URLClassLoader ucl = new URLClassLoader(new URL[] {new File("c:/pos/example.jar").toURI().toURL()});
        System.out.println(Arrays.asList(ucl.loadClass("org.popper.example.pages.Login").getAnnotations()));
    }

    public PopperServlet() throws MalformedURLException, ClassNotFoundException {
        URLClassLoader ucl = new URLClassLoader(new URL[] {new File("c:/pos/example.jar").toURI().toURL()});
        System.out.println(Arrays.asList(ucl.loadClass("org.popper.example.pages.Login").getAnnotations()));
   }
}

以main身份运行代码可显示预期结果

[@org.popper.fw.annotations.Page(name=Login)]

在Tomcat中将代码作为servlet运行无法找到注释

[]

谁能告诉我为什么？

Answer 1

和以前一样：关注类加载器层次结构！

new URLClassLoader(new URL[] {new File("c:/pos/example.jar").toURI().toURL()}, PopperServlet.class.getClassloader());

做到了。但是令人惊讶的是，没有找到注解而是a ClassNotFoundException或NoClassDefError，这就是我在加载类时未找到注解的期望值...