Scala反序列化：找不到类 [英] Scala deserialization: class not found

问题描述

我试图理解在尝试序列化/反序列化一个非常简单的数据结构时出现的以下问题：

I'm trying to understand the following issue that occurs when trying to serialize/deserialize a very simple data structure:

case class SimpleClass(i: Int)

object SerializationDebug {

  def main(args: Array[String]) {
    val c = SimpleClass(0)
    val l1 = List(c)

    serializationSaveToFile("test", l1)
    val l2 = serializationLoadFromFile("test") // .asInstanceOf ...
  }

  def serializationSaveToFile(fn: String, o: Any) {
    val fos = new FileOutputStream(fn)
    val oos = new ObjectOutputStream(fos)
    oos.writeObject(o)
    oos.close()
  }

  def serializationLoadFromFile(fn: String): Any = {
    val fis = new FileInputStream(fn)
    val ois = new ObjectInputStream(fis)
    return ois.readObject()
  }  
}

尝试运行此代码时，我得到 java.lang.ClassNotFoundException：SimpleClass 在反序列化步骤中。我调查的当前结果是：

When trying to run this code I get java.lang.ClassNotFoundException: SimpleClass in the deserialization step. The current results of my investigations are:

• 当我交换 SimpleClass 时，该示例起作用通过一些内置类型，即，我可以反序列化 List [Int] 或 List [（Int，Double）] 没有问题。再次将内置类型与我的 SimpleClass 混合（即具有 List [Any] ）会引发异常。


• 我试图在其他范围内定义 SimpleClass （例如，嵌套在对象或本地范围内），但没有任何改变。另外，使用普通的（非大小写的）类扩展 Serializable 也会得到相同的结果。


• 更令人困惑的是，使用 Array [SimpleClass] 代替 List 确实有效！尝试其他容器可确认这种奇怪的不一致：在可变映射中将 SimpleClass 作为类型参数作为不可变映射有效，

• The example works when I exchange SimpleClass by some built-in type, i.e., I can deserialize List[Int] or List[(Int, Double)] without a problem. Mixing built-in types with my SimpleClass (i.e. having a List[Any]) again throws an exception.
• I tried to define SimpleClass in other scopes (for instance nested in the object or in the local scope even) but that did not change anything. Also, having a normal (non-case) class extending Serializable gives the same result.
• Even more puzzling is that using an Array[SimpleClass] instead of List does work! Trying other containers confirms this strange inconsistency: having SimpleClass as type parameter within an immutable map works, in case of a mutable map I get the exception.

重要的是：我的Scala版本为2.10.0； JDK是1.7.0。

In case it matters: My Scala version is 2.10.0; JDK is 1.7.0.

这是怎么回事？这应该失败还是某种错误？我手头的实际问题涉及到更为复杂的数据结构（大量嵌套；内置类和自己的类的混合）。任何以最小干扰的简单方式（即不必查找容器类及其类型参数的有效组合）来序列化/反序列化此数据结构的建议也都欢迎！

What is going on here? Is this supposed to fail or is it some kind of bug? My actual problem at hand involves a much more complex data structure (a lot of nesting; mixture of built-in and own classes). Any suggestions to serializing/deserializing this data structure in a minimal-intrusive simple way (i.e. without having to find working combinations of container classes and their type parameters) are also welcome!

推荐答案

此解决方案对我来说效果很好：

This solution works fine for me:

val ois = new ObjectInputStream(new FileInputStream(fileName)) {
  override def resolveClass(desc: java.io.ObjectStreamClass): Class[_] = {
    try { Class.forName(desc.getName, false, getClass.getClassLoader) }
    catch { case ex: ClassNotFoundException => super.resolveClass(desc) }
  }
}

当然，当写入对象，我们使用相同的方式：

of course, when writing object, we use the same way:

val ois = new ObjectOutputStream(new FileOutputStream(path))
ois.writeObject(myobject)

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