xStream 1.4.17 error with apache.common.collections.BidiMap.DualHashBidiMap

[Vipul Gupta]

Is there any way I can properly serialize and deserialize unserializable-parent object in xStream-1.4.17.

For e.g - While using DualHashBidiMap of apache commons.collections in the following
code -
```
> DualHashBidiMap db = new DualHashBidiMap();

> db.put(1,2);

> XStream xStream=new XStream(new DomDriver());

> String xml = xStream.toXML(db);

> DualHashBidiMap db2 = (DualHashBidiMap)xStream.fromXML(xml);
```

I am getting following xml -

```
<org.apache.commons.collections.bidimap.DualHashBidiMap serialization="custom">

<unserializable-parents/>

<org.apache.commons.collections.bidimap.DualHashBidiMap>

<default/>

<map>

<entry>

<int>1</int>

<int>2</int>

</entry>

</map>

</org.apache.commons.collections.bidimap.DualHashBidiMap>
```

But while deserializing the same XML string, I am getting `java.lang.NullPointerException`.

One workAround that I found is to register a converter for DualHashBidiMap class as follows -
```
>xStream.register(new MapConverter(xStream.getMapper(),DualHashBidiMap.class);
```

So my question is, Is there any way I can make this work for any such class without registering a converter for it.
I apologize in advance for any naiveness. As I am not too familiar with xStream.

Best,

Vipul

[Jörg Schaible]

Hi,

On Friday, 25. June 2021, 08:02:57 CEST Vipul Gupta wrote:
> Is there any way I can properly serialize and deserialize
> unserializable-parent object in xStream-1.4.17.
>
> For e.g - While using DualHashBidiMap of apache commons.collections in the
> following
> code -
> ```

> *> DualHashBidiMap db = new DualHashBidiMap();*
> *> db.put(1,2);*
> *> XStream xStream=new XStream(new DomDriver());*
> *> String xml = xStream.toXML(db);*
>
> *> DualHashBidiMap db2 = (DualHashBidiMap)xStream.fromXML(xml);*```

>
> I am getting following xml -
> ```

> *<org.apache.commons.collections.bidimap.DualHashBidiMap
> serialization="custom">*
> *<unserializable-parents/>*
> *<org.apache.commons.collections.bidimap.DualHashBidiMap>*
> *<default/>*
> *<map>*
> *<entry>*
> *<int>1</int>*
> *<int>2</int>*
> *</entry>*
> *</map>*
> *</org.apache.commons.collections.bidimap.DualHashBidiMap>*
> ```

>
> But while deserializing the same XML string, I am getting
> `java.lang.NullPointerException`.

Normally it works OOTB. Did you also try Java serialization - does that work?
Please provide a stack trace.

> One workAround that I found is to register a converter for DualHashBidiMap
> class as follows -
> ```
>
> >xStream.register(new
>
> MapConverter(xStream.getMapper(),DualHashBidiMap.class);
> ```

This means, that it is handled as an arbitrary Map implementation without any
support for special implementation details.

> So my question is, Is there any way I can make this work for any such class
> without registering a converter for it.

As said, it should work OOTB, but somewhere is an error.

> I apologize in advance for any naiveness. As I am not too familiar with
> xStream.

Your welcome,
Jörg

[Vipul Gupta]

Java serialization works just fine. 

Please provide a stack trace.

Here is the complete stack trace - 
---

Security framework of XStream not explicitly initialized, using predefined black list on your own risk.
com.thoughtworks.xstream.converters.ConversionException: Failed calling method
---- Debugging information ----
message : Failed calling method
cause-exception : java.lang.NullPointerException
cause-message : null
method : org.apache.commons.collections.bidimap.DualHashBidiMap.readObject()
class : org.apache.commons.collections.bidimap.DualHashBidiMap
required-type : org.apache.commons.collections.bidimap.DualHashBidiMap
converter-type : com.thoughtworks.xstream.converters.reflection.SerializableConverter
path : /org.apache.commons.collections.bidimap.DualHashBidiMap/org.apache.commons.collections.bidimap.DualHashBidiMap
version : 1.4.17
at com.thoughtworks.xstream.core.util.SerializationMembers.callReadObject(SerializationMembers.java:136)
at com.thoughtworks.xstream.converters.reflection.SerializableConverter.doUnmarshal(SerializableConverter.java:443)
at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshal(AbstractReflectionConverter.java:277)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:72)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1431)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1411)
at com.thoughtworks.xstream.XStream.fromXML(XStream.java:1296)
at com.thoughtworks.xstream.XStream.fromXML(XStream.java:1287)
at com.cisco.main.SerializerMain.normalserialization(SerializerMain.java:131)
at com.cisco.main.SerializerMain.main(SerializerMain.java:65)
Caused by: java.lang.NullPointerException
at org.apache.commons.collections.bidimap.DualHashBidiMap.readObject(DualHashBidiMap.java:101)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at com.thoughtworks.xstream.core.util.SerializationMembers.callReadObject(SerializationMembers.java:132)

... 14 more 

----

> One workAround that I found is to register a converter for DualHashBidiMap
> class as follows -
> ```
>
> >xStream.register(new
>
> MapConverter(xStream.getMapper(),DualHashBidiMap.class);
> ```

This means, that it is handled as an arbitrary Map implementation without any
support for special implementation details.

> So my question is, Is there any way I can make this work for any such class
> without registering a converter for it.

As said, it should work OOTB, but somewhere is an error.

> I apologize in advance for any naiveness. As I am not too familiar with
> xStream.

Your welcome,
Jörg

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[Jörg Schaible]

Hi,

actually, I verified that this is a special case where XStream fails. You will have to open an issue at Github:

https://github.com/x-stream/xstream/issues

Hwoever, with the current version you won't get this object processed without further setup.

Regards,

Jörg