3

我有一个接口的名称，我想调用一个由其具体实现的类定义的方法。所以我求助于Java Reflection。

界面：

package tsb.learning.reflection;

public interface IAnyThing {

    void doSomething();
}

它的实现类：

package tsb.learning.reflection;

public class AnyThing implements IAnyThing {

    public void doSomething() {
        System.out.println("JYM");
    }
}

的实施InvocationHandler：

package tsb.learning.reflection;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class AnyInvocationHandler implements InvocationHandler {

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        return method.invoke(proxy, args);
    }
}

和控制器：

package tsb.learning.reflection;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

public class Controller {

    /**
     * @param args
     * @throws ClassNotFoundException
     */
    public static void main(String[] args) throws ClassNotFoundException {
        String interfaceName = "tsb.learning.reflection.IAnyThing";
        ClassLoader classLoader = Class.forName(interfaceName).getClassLoader();
        Class<?>[] interfaces = new Class<?>[] { Class.forName(interfaceName) };
        InvocationHandler handler = new AnyInvocationHandler();
        IAnyThing anyThing = (IAnyThing) Proxy.newProxyInstance(classLoader, interfaces, handler);
        anyThing.doSomething();
    }
}

但它不起作用，我收到以下异常：

Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at tsb.learning.reflection.AnyInvocationHandler.invoke(AnyInvocationHandler.java:10)
    at $Proxy0.doSomething(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at tsb.learning.reflection.AnyInvocationHandler.invoke(AnyInvocationHandler.java:10)
    at $Proxy0.doSomething(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at tsb.learning.reflection.AnyInvocationHandler.invoke(AnyInvocationHandler.java:10)
    at $Proxy0.doSomething(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at tsb.learning.reflection.AnyInvocationHandler.invoke(AnyInvocationHandler.java:10)

例外是在控制台中循环打印，我需要停止程序。

任何信息都会对我很有帮助。

4

3 回答 3

4

引起：java.lang.reflect.InvocationTargetException

这意味着您调用的方法引发了异常。您需要查看出现在它之后的异常并导致此异常。它与您如何调用该方法无关。

我怀疑你得到了 StackOverflowError

// calls the same method on the same proxy which will recurse until you get an error.
return method.invoke(proxy, args);

而是尝试在真实对象上调用方法来做某事。

public class AnyInvocationHandler implements InvocationHandler {
    final IAnyThing iat;

    public AnyInvocationHandler(IAnyThing iat) {
        this.iat = iat;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        // call the same method on a real object.
        return method.invoke(iat, args);
    }
}

顺便说一句你可以写

Class interfaceClass = tsb.learning.reflection.IAnyThing.class;
ClassLoader classLoader = interfaceClass.getClassLoader();
Class<?>[] interfaces = new Class<?>[] { interfaceClass };
于 2012-11-28T17:41:23.080 回答
1

在您的内部AnyInvocationHandler，您可以将调用委托给您的实例AnyThing：

public class AnyInvocationHandler implements InvocationHandler {

    private AnyThing delegate = new AnyThing();

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        // to something useful here
        [...]
        // finally, invoke the method on implementation class.
        return method.invoke(delegate, args);
    }
}
于 2012-11-28T17:47:21.843 回答
1

中唯一的方法IAnyThing是doSomething()，所以我猜InvocationHandler你知道方法是什么。把你的实现放在那里。此外，doSomething()您还应该处理继承自的三个方法java.lang.Object：

public static class AnyInvocationHandler implements InvocationHandler {

    private static final Method doSomething;

    static {
        try {
            doSomething = IAnyThing.class.getMethod("doSomething");
        } catch (NoSuchMethodException e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (method.getDeclaringClass() == Object.class)
            return handleObjectMethod(proxy, method, args);

        if (doSomething.equals(method)) {
            doSomethingImpl();
            return null;
        }

        throw new AbstractMethodError(method.toString());
    }

    private Object handleObjectMethod(Object proxy, Method method, Object[] args) {
        switch (method.getName()) {
            case "equals":
                return proxy == args[0];
            case "hashCode":
                return System.identityHashCode(proxy);
            case "toString":
                return proxy.getClass().getName() + "@" + Integer.toHexString(System.identityHashCode(proxy));
            default:
                throw new AssertionError();
        }
    }

    private void doSomethingImpl() {
        // implement....
    }

}
于 2012-11-28T18:07:16.913 回答