Question

我正在尝试在Android上使用Bouncycastle读取ASN1对象。我希望它是一个DERSequence，它在Bouncycastle中是ASN1Sequence的子类，它是ASN1Object的子类。

import org.bouncycastle.asn1.ASN1InputStream;
import org.bouncycastle.asn1.ASN1Object;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.DERSequence;
...

ASN1InputStream ais = ...;
Object o = ais.readObject();
// Eclipse's debugger now says o is a DERSequence, as expected.

DERSequence o2 = (DERSequence)o;
ASN1Sequence o3 = o2;
ASN1Object o4 = o3;
// And o4 is now exactly what I want.

ASN1Object o5 = (ASN1Object)o;
// But this throws:
///    java.lang.ClassCastException: org.bouncycastle.asn1.DERSequence

根据答案的反馈，我构建了另一个较短的例子：

Object o = new DERSequence();
ASN1Object o1 = new DERSequence(); // This behaves fine.
ASN1Object o2 = (ASN1Object)o; // Throws ClassCastException.

导致此演员失败的原因是什么？

Answer 1

Android在此处有一个修改过的类层次结构，请参阅http://www.netmite.com/android/mydroid/1.5/dalvik/libcore/security/src/main/java/org/bouncycastle/asn1/ASN1Sequence.java中的注释您是否完全确定您使用的版本是DERSequence是ASN1Object的子类型？

例如，它在http://www.eecs.berkeley.edu/~jonah/bc/org/bouncycastle/asn1/DERSequence.html

但不是http://www.androidjavadoc.com/m3-rc37a/org/bouncycastle/asn1/DERSequence.html

Answer 2

你能尝试执行这个：

package classtest;

import org.bouncycastle.asn1.ASN1Object;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.DERSequence;

public class A {

    public static void main(String[] args) {
        testCast(new DERSequence());
    }

    private static void testCast(Object o) {
        DERSequence o2 = (DERSequence) o;
        ASN1Sequence o3 = o2;
        ASN1Object o4 = o3;

        ASN1Object o5 = (ASN1Object) o;
    }

}

（对我来说，这不会引发任何异常）

如果这不起作用，你应该检查vickirk的答案

如果A扩展B扩展C，为什么我可以转换为A但是得到一个ClassCastException转换为C？

2 个答案: