Java XStream Deep Copy 引发异常 ObjectAccessException [英] Java XStream Deep Copy raises Exception ObjectAccessException

问题描述

我有一个用于克隆的 XStream.这是我的简单代码，我没有太多专业知识.

I have a XStream for cloning. Here is my simple code, I have not much expertise with it.

com.thoughtworks.xstream.XStream XSTREAM = new com.thoughtworks.xstream.XStream();

稍后我将克隆实例存储在一个哈希表中(我知道存储在它上面不是一个好主意，但它是一个遗留系统).

Later I store the clone instances in a hashTable (I know is not very good idea storing on it but is a legacy system).

我将它存储为 Student 的一个类，然后我存储(克隆)Student 的另一个实例并提出.

I store it a class of Student, later I store (clone) other instance of Student and raises.

com.thoughtworks.xstream.converters.reflection.ObjectAccessException: Could not call com.model.Student_$$_javassist_83.writeReplace():null java.lang.NullPointerException

这是我用于存储克隆对象的代码.

Here is my code for storing the clone objects.

public void keep(String key, Object value) 
{
    Object obj = XSTREAM.fromXML(XSTREAM.toXML(value));
    storage.put(key,obj);
}

我认为这是出现问题的源代码.[XStream 来源.][片段]

I think here is the source code where the problem is arising. [XStream sources.][Snippet]

 public Object callWriteReplace(Object object) 
 {             
              Method writeReplaceMethod = getMethod(object.getClass(), "writeReplace", null, true);
              if (writeReplaceMethod != null) {
                  try {
                      Object[] EMPTY_ARGS = new Object[0];
                      return writeReplaceMethod.invoke(object, EMPTY_ARGS);
                  } catch (IllegalAccessException e) {
                      throw new ObjectAccessException("Could not call " + object.getClass().getName() + ".writeReplace()", e);
                  } catch (InvocationTargetException e) {
                      throw new ObjectAccessException("Could not call " + object.getClass().getName() + ".writeReplace()", e.getTargetException());
                  }
             } else {
                  return object;
              }              
      }

我希望有人能指导我，我对这个话题有点迷茫.

I hope somebody can guide me, I am a little lost on this topic.

这是痕迹.当我清理 clazz 示例 student.setListOfPhones(null) 的依赖项时，它似乎有效；异常是在图中的 2 或 3 级抛出.根据 XStream 的说法，为什么会这样:

Here is the trace. It seems when I clean the dependences of the clazz example student.setListOfPhones(null) it works; the exception is throw on the 2 or 3 level in the graph. Why is this according to XStream it says:

使其适用于具有高消息吞吐量的大型对象图或系统.

making it suitable for large object graphs or systems with high message throughput.

堆栈跟踪:

com.thoughtworks.xstream.converters.reflection.ObjectAccessException: Could not call com.model.Subjects_$$_javassist_224.writeReplace() : null
java.lang.NullPointerException
at javassist.util.proxy.RuntimeSupport$DefaultMethodHandler.invoke(RuntimeSupport.java:37)
at com.model.Subjects_$$_javassist_224.writeReplace(Subject_$$_javassist_224.java)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.thoughtworks.xstream.converters.reflection.SerializationMethodInvoker.callWriteReplace(SerializationMethodInvoker.java:88)
at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.marshal(AbstractReflectionConverter.java:60)
at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:69)
at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:58)
at com.thoughtworks.xstream.core.AbstractReferenceMarshaller$1.convertAnother(AbstractReferenceMarshaller.java:84)
at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.marshallField(AbstractReflectionConverter.java:229)
at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$2.writeField(AbstractReflectionConverter.java:208)
at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$2.<init>(AbstractReflectionConverter.java:171)
at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doMarshal(AbstractReflectionConverter.java:116)
at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.marshal(AbstractReflectionConverter.java:72)
at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:69)
at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:58)
at com.thoughtworks.xstream.core.AbstractReferenceMarshaller$1.convertAnother(AbstractReferenceMarshaller.java:84)

推荐答案

我已经解决了这个问题是另一种方法是在这个类 Student 上创建一个浅拷贝，当然当 XStream 得到这个类时，关系不够深对于 XStream 和 NullPointerException 是 Throw.. 感谢戴夫上帝保佑.

hi i have solved the problem was another method was creating a shallow copy on this class Student and of course when XStream got the class the relationship wasn't deep enough for XStream and NullPointerException was Throw.. thank Dave god Bless.

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