无法从 tomcat 中自定义类加载器加载的类中获取注释 [英] Can't get annotations from classes loaded by custom classloader in tomcat

问题描述

给定类 org.popper.example.pages.Login

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

导出到c:\pos\example.jar和下面的servlet

exported to c:\pos\example.jar and the following 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 方式运行代码显示预期结果

Running the code as main shows the expected result

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

在tomcat中以servlet的形式运行代码没有找到注解

Running the code as servlet in tomcat doesn't find the annotations

[]

谁能告诉我为什么?

推荐答案

和往常一样:注意类加载器层次结构！

It's the same as always: Regard the classloader-hierarchy!

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

成功了.但令人惊讶的是，没有找到注释而是 ClassNotFoundException 或 NoClassDefError，这就是我在加载类时找不到注释时的预期......

did the trick. But it's surprising that annotations aren't found instead a ClassNotFoundException or NoClassDefError, thats what I expected when annotations are not found when loading a class...

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