使用代理时，类加载器看不到接口?

问题描述

当我尝试使用动态代理时，我看到以下异常

I am seeing following exception when I try to use dynamic proxy

 com.intellij.rt.execution.application.AppMain DynamicProxy.DynamicProxy
Exception in thread "main" java.lang.IllegalArgumentException: interface Interfaces.IPerson is not visible from class loader
    at java.lang.reflect.Proxy.getProxyClass(Proxy.java:353)
    at java.lang.reflect.Proxy.newProxyInstance(Proxy.java:581)
    at DynamicProxy.Creator.getProxy(Creator.java:18)
    at DynamicProxy.DynamicProxy.main(DynamicProxy.java:54)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

知道我需要做什么来解决它

Any idea what I need to do to resolve it

推荐答案

如果这是 Web 应用程序，那么在创建动态代理时应该使用 Web 应用程序类加载器.因此，例如，而不是:

If this is web application, then you should use the web application classloader when creating dynamic proxy. So, for example instead of:

Proxy.newProxyInstance(
  ClassLoader.getSystemClassLoader(),
  new Class < ? >[] {MyInterface.class},
  new InvocationHandler() {
    // (...)
});

试试:

Proxy.newProxyInstance(
  this.getClass().getClassLoader(), // here is the trick
  new Class < ? >[] {MyInterface.class},
  new InvocationHandler() {
    // (...)
});

例如，tomcat 类加载器的层次结构(其他 Web 容器也类似)如下:

For instance, hierarchy of tomcat class loaders (other web containers have similar) is following:

      Bootstrap
          |
       System
          |
       Common
       /
  Webapp1   Webapp2 ...

它是 webapp 类加载器，它包含 Web 应用程序/WEB-INF/classes 目录中的类和资源，以及 Web 应用程序/WEB-INF/lib 目录下 JAR 文件中的类和资源.

And it is the webapp classloader which contains classes and resources in the /WEB-INF/classes directory of your web application, plus classes and resources in JAR files under the /WEB-INF/lib directory of your web application.

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