Java转换/类加载器问题 [英] Java casting / classloader issues

问题描述

这是问题的简化版本：

 SomeClass c = (SomeClass) obj.getSomeClassParent()

不总是，但有时会触发异常

not always but it happens sometimes to trigger exception

 org.somepackage.SomeClass can't be cast to org.somepackage.SomeClass 

这是怎么可能的？我想它有一些事实与JAI imageio是本机lib，但中继这怎么可能发生？我可能错过了什么，但什么？

How is this possible ? I suppose it has something to do with the fact that JAI imageio is native lib, but relay how can this happen ? I'm probably missing something but what ?

I'm using JAI imageio version 1.1 
dcm4che 2.0.21  DICOM lib

以下是原始代码

  ImageInputStream iis = ImageIO.createImageInputStream(src);
  Iterator<ImageReader> iter = ImageIO.getImageReadersByFormatName("DICOM");
  ImageReader reader = iter.next();
  DicomImageReadParam param = (DicomImageReadParam) reader.getDefaultReadParam();

原始异常

org.dcm4che2.imageio.plugins.dcm.DicomImageReadParam can't be cast to    
org.dcm4che2.imageio.plugins.dcm.DicomImageReadParam

推荐答案

我认为如果

1. a SomeClass 实例从ClassLoader X加载（因此它的类是CL X的 SomeClass 或者让我们调用它： code> CL（X）.SomeClass ）


2. ，但它是在不同的类加载器。例如。当前Threads类加载器是Y，因此 SomeClass 实际上是 CL（Y）.SomeClass

1. a SomeClass instance was loaded from ClassLoader X (so its class is SomeClass of CL X or let's call it: CL(X).SomeClass)
2. but it is being cast in a different class loader. E.g. the current Threads class loader is Y so SomeClass is actually CL(Y).SomeClass

所以你有：

• 实例类= CL（X）.SomeClass


• class cast target = li>


• instance class = CL(X).SomeClass
• class cast target = CL(Y).SomeClass

或者换句话说 - 不是同一个类 - 因此类转换异常。

Or in other words - not the same class - thus the class cast exception.

可能的副本： ClassCastException当投射到同一类 - 它也有一些好的建议。

Possible duplicate of: ClassCastException when casting to the same class - it has some good suggestions as well.

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