Java - 反序列化包含原始类型的哈希表时出错

Question

我已经连载了HashTable<String,Object>使用 ObjectOutputStream 的对象。序列化对象时，没有出现异常，但反序列化时，出现以下异常:

Exception in thread "main" java.io.InvalidClassException: java.lang.Long; local class
incompatible: stream classdesc serialVersionUID = 4290774032661291999, local class
serialVersionUID = 4290774380558885855

当我删除 HashTable 中的所有键时，我不再收到错误消息其值不是 String (我删除的所有键/值对都有一个原始类型作为它们的值)。

什么可能导致此错误？

更新 - 这是代码

public static String serialize(Quiz quiz) throws IOException{
    HashMap<String,Object> quizData = new HashMap<String,Object>();
    quizData.put("version", 0); //int
    quizData.put("name", quiz.getName()); //String
    quizData.put("desc", quiz.getDesc()); //String
    quizData.put("timelimitType", quiz.getTimelimitType()); //String
    quizData.put("timelimit", quiz.getTimelimit()); //long
    ArrayList<String> serializedQuestionsData = new ArrayList<String>();
    for (Question question : quiz.getQuestions())
        serializedQuestionsData.add(Question.serialize(question));
    quizData.put("questions", serializedQuestionsData.toArray(new String[0])); //String[]
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos;
    try { oos = new ObjectOutputStream(baos); } catch (IOException error){ throw error; }
    try { oos.writeObject(quizData); } catch (IOException error){ throw error; }
    return baos.toString();
}
@SuppressWarnings("unchecked")
public static Quiz deserialize(String serializedQuizData) throws IOException, ClassNotFoundException{
    ByteArrayInputStream bais = new ByteArrayInputStream(serializedQuizData.getBytes());
    ObjectInputStream ois;
    try { ois = new ObjectInputStream(bais); } catch (IOException error){ throw error; }
    HashMap<String,Object> quizData;
    // Exception occurs on the following line!!
    try { quizData = (HashMap<String,Object>) ois.readObject(); } catch (ClassNotFoundException error){ throw error; }
    Quiz quiz;
    if ((int) quizData.get("version") == 0){
        quiz = new Quiz((String) quizData.get("name"),
                (String) quizData.get("desc"),
                (String) quizData.get("timelimitType"),
                (long) quizData.get("timelimit"));
        for (String serializedQuestionData : (String[]) quizData.get("questions"))
            quiz.addQuestion(Question.deserialize(serializedQuestionData));
    } else {
        throw new UnsupportedOperationException("Unsupported version: \"" + quizData.get("version") + "\"");
    }
    return quiz;
}

Answer 1

问题在于您正在使用 toString() 将字节数组输出流转换为字符串。 toString() 方法只是使用平台默认编码将字节(根本不表示字符，而是纯粹的二进制数据)转换为字符串。因此，这是一个有损操作，因为您的平台默认编码没有为每个可能的字节提供有效字符。

您不应该使用 String 来保存二进制数据。字符串包含字符。如果您确实需要字符串，请使用十六进制或 Base64 编码器对字节数组进行编码。否则，只需使用字节数组来保存二进制数据:

public static byte[] serialize(Quiz quiz) throws IOException{
    ...
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ...
    return baos.toByteArray();
}

@SuppressWarnings("unchecked")
public static Quiz deserialize(byte[] serializedQuizData) throws IOException, ClassNotFoundException{
    ByteArrayInputStream bais = new ByteArrayInputStream(serializedQuizData);
    ...
    return quiz;
}