Java.lang.reflect.Proxy 从调用返回另一个代理导致赋值时出现 ClassCastException

Question

所以我在玩 geotools，我想我应该代理他们的一个数据访问类，并跟踪它是如何在他们的代码中使用的。

我编写了一个动态代理，并在其中包装了一个 FeatureSource(接口(interface))，然后一切顺利。然后我还想看看 featureSource 返回的一些传递对象，因为 FeatureSource 所做的主要事情是返回一个 FeatureCollection(FeatureSource 类似于 sql 数据源，featurecollection 类似于 sql 语句)。

在我的 invocationhandler 中，我只是将调用传递给底层对象，打印出目标类/方法/args 和结果，但是对于返回 FeatureCollection(另一个接口(interface))的调用，我将该对象包装在我的代理(同一个类但是一个新实例，应该无关紧要吧？)并返回它。砰!类播异常:

java.lang.ClassCastException: $Proxy5 cannot be cast to org.geotools.feature.FeatureCollection  
    at $Proxy4.getFeatures(Unknown Source)  
    at MyClass.myTestMethod(MyClass.java:295)  

调用代码:

FeatureSource<SimpleFeatureType, SimpleFeature> featureSource = ... // create the FS
featureSource = (FeatureSource<SimpleFeatureType, SimpleFeature>) FeatureSourceProxy.newInstance(featureSource, features);
featureSource.getBounds();// ok
featureSource.getSupportedHints();// ok

DefaultQuery query1 = new DefaultQuery(DefaultQuery.ALL);
FeatureCollection<SimpleFeatureType, SimpleFeature> results = featureSource.getFeatures(query1); //<- explosion here

代理:

public class FeatureSourceProxy  implements java.lang.reflect.InvocationHandler {

private Object target;
private List<SimpleFeature> features;

public static Object newInstance(Object obj, List<SimpleFeature> features) {
return java.lang.reflect.Proxy.newProxyInstance(
    obj.getClass().getClassLoader(), 
    obj.getClass().getInterfaces(), 
    new FeatureSourceProxy(obj, features)
);
}

private FeatureSourceProxy(Object obj, List<SimpleFeature> features) {
this.target = obj;
this.features = features;
}

public Object invoke(Object proxy, Method m, Object[] args)throws Throwable{
Object result = null;
try {
    if("getFeatures".equals(m.getName())){ 
        result = interceptGetFeatures(m, args);
    }
    else{
        result = m.invoke(target, args);
    }
} 
catch (Exception e) {
    throw new RuntimeException("unexpected invocation exception: " +  e.getMessage(), e);
} 
return result;
}

private Object interceptGetFeatures(Method m, Object[] args) throws Exception{
    return newInstance(m.invoke(target, args), features);
}

是否可以从代理接口(interface) 动态返回接口(interface)代理，或者我做错了什么？干杯!

Answer 1

Class.getInterfaces() 只返回类直接实现的接口(interface)。您需要一个传递闭包来获取所有接口(interface)。

更新

例子:

private static Class<?>[] getInterfaces(Class<?> c) {
    List<Class<?>> result = new ArrayList<Class<?>>();
    if (c.isInterface()) {
        result.add(c);
    } else {
        do {
            addInterfaces(c, result);
            c = c.getSuperclass();
        } while (c != null);
    }
    for (int i = 0; i < result.size(); ++i) {
        addInterfaces(result.get(i), result);
    }
    return result.toArray(new Class<?>[result.size()]);
}

private static void addInterfaces(Class<?> c, List<Class<?>> list) {
    for (Class<?> intf: c.getInterfaces()) {
        if (!list.contains(intf)) {
            list.add(intf);
        }
    }
}

您可能还需要“解包”作为参数传递的代理。