Java Reading XML with XStream

Question

I'm trying to deserialize this XML file using XStream and I'm getting this error

Exception in thread "main" com.thoughtworks.xstream.converters.ConversionException: Authors : Authors
---- Debugging information ----
message             : Authors
cause-exception     : com.thoughtworks.xstream.mapper.CannotResolveClassException
cause-message       : Authors
class               : java.util.ArrayList
required-type       : java.util.ArrayList
converter-type      : com.thoughtworks.xstream.converters.collections.CollectionConverter
path                : /ListOfDBook/DBook/Authors
class[1]            : com.test.books.ListOfDBook
converter-type[1]   : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
version             : null
-------------------------------
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:79)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshallField(AbstractReflectionConverter.java:355)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doUnmarshal(AbstractReflectionConverter.java:306)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshal(AbstractReflectionConverter.java:234)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
    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:1058)
    at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1042)
    at com.thoughtworks.xstream.XStream.fromXML(XStream.java:922)
    at com.test.booktest.BookImport.getBooks(BookImport.java:34)
    at com.test.booktest.Client.main(Client.java:6)
Caused by: com.thoughtworks.xstream.mapper.CannotResolveClassException: Authors
    at com.thoughtworks.xstream.mapper.DefaultMapper.realClass(DefaultMapper.java:56)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.DynamicProxyMapper.realClass(DynamicProxyMapper.java:55)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.PackageAliasingMapper.realClass(PackageAliasingMapper.java:88)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.ClassAliasingMapper.realClass(ClassAliasingMapper.java:79)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.ArrayMapper.realClass(ArrayMapper.java:74)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
    at com.thoughtworks.xstream.mapper.CachingMapper.realClass(CachingMapper.java:45)
    at com.thoughtworks.xstream.core.util.HierarchicalStreams.readClassType(HierarchicalStreams.java:29)
    at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.readItem(AbstractCollectionConverter.java:70)
    at com.thoughtworks.xstream.converters.collections.CollectionConverter.addCurrentElementToCollection(CollectionConverter.java:79)
    at com.thoughtworks.xstream.converters.collections.CollectionConverter.populateCollection(CollectionConverter.java:72)
    at com.thoughtworks.xstream.converters.collections.CollectionConverter.populateCollection(CollectionConverter.java:66)
    at com.thoughtworks.xstream.converters.collections.CollectionConverter.unmarshal(CollectionConverter.java:61)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
    ... 16 more

With this XML

<ListOfDBook xmlns="Test.Books" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
    <DBook>
        <Authors>
            <DAuthor>
                <Name>Google</Name>
                <Url>http://google.com</Url>
            </DAuthor>
        </Authors>
    </DBook>
</ListOfDBook>

With these classes

//ListOfDBook.java
public class ListOfDBook {
    public ArrayList<DBook> DBook; 
}

//DBook.java
public class DBook {
    public ArrayList<DAuthor> Authors;
}

//DAuthor.java
public class DAuthor {
    String Name;
    String Url;
}

//BookImport.java
import com.test.books.*;
XStream xstream = new XStream(new DomDriver());
xstream.alias("ListOfDBook", ListOfDBook.class);
InputStream in = new FileInputStream("Books.xml");
ListOfDBook = (ListOfDBook)xstream.fromXML(in);

I recreated the classes from reading the XML file and changing the XML file is not an option. Am I doing something completely wrong?

I don't think your last line is right, there is no variable name. — jn1kk, Aug 17 '13 at 18:29

jn1kk · Accepted Answer · 2014-04-16T21:50:18.657

6

You are missing Authors?

//ListOfDBook.java
public class ListOfDBook {
    public ArrayList<DBook> DBook; 
}

//DBook.java
public class DBook {
    public ArrayList<Author> Authors;
}

//Author.java
public class Author {
    public ArrayList<DAuthor> DAuthors;
}

//DAuthor.java
public class DAuthor {
    String Name;
    String Url;
}

EDIT 2:

You need to use addImplicitCollection.

import java.util.*;
import com.thoughtworks.xstream.*;
import com.thoughtworks.xstream.io.*;
import com.thoughtworks.xstream.io.xml.*;
import java.io.*;

public class Test {

    public static void main(String[] args) throws Exception {

        XStream xstream = new XStream(new DomDriver());
        xstream.alias("ListOfDBook", ListOfDBook.class);
        xstream.alias("DBook", DBook.class);
        xstream.alias("Authors", Authors.class);
        xstream.alias("DAuthor", DAuthor.class);
        xstream.addImplicitCollection(Authors.class, "dauthors");
        xstream.addImplicitCollection(DBook.class, "authors");
        xstream.addImplicitCollection(ListOfDBook.class, "dbooks");
        InputStream in = new FileInputStream("Books.xml");
        ListOfDBook var = (ListOfDBook)xstream.fromXML(in);

    }

}

//ListOfDBook.java
class ListOfDBook {
    public List<DBook> dbooks = new LinkedList<DBook>(); 
}

//DBook.java
class DBook {
    public List<Authors> authors = new LinkedList<Authors>();
}

//Authors.java
class Authors {
    public List<DAuthor> dauthors = new LinkedList<DAuthor>();
}

//DAuthor.java
class DAuthor {
    public String Name;
    public String Url;
}

edited Apr 16 '14 at 21:50

answered Aug 17 '13 at 18:01

jn1kk

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You are correct I was missing Author. It then moves onto the Name element and have the same error. `com.thoughtworks.xstream.converters.ConversionException: Name : Name` I feel like I don't completely understand how I should be setting out the classes. – user2686811 Aug 17 '13 at 18:12
Try aliasing the custom classes, check this link: http://xstream.codehaus.org/tutorial.html Also, try lowercase variable names. – jn1kk Aug 17 '13 at 18:30
Creating the Class 'Name' fixes that and the same happens for the next element, 'Url'. I can't be making a new class for every different element when the element should be part of the parent element right? – user2686811 Aug 17 '13 at 18:33
No You do not need a custom class for the Strings. Try using lowercase variable names first. – jn1kk Aug 17 '13 at 18:35
Same error with lowercase. Tried adding this to DAuthor class `public DAuthor(String Name, String URL) { this.name = Name; this.url = URL; }` also did nothing. – user2686811 Aug 17 '13 at 18:42
If I set `xstream.alias("Name", DAuthor.class);` it works. Is this correct? Do I need to set an alias for each variable? EDIT: I don't think that's right though, even if I set the alias to point to `ArrayOfDBook` it accepts it even though there is no Name variable in that class. – user2686811 Aug 17 '13 at 19:02
Thanks! That seems to have fixed it. I guess I need to do that for all the Lists of custom objects. Thanks a lot for your time – user2686811 Aug 17 '13 at 19:25

Java Reading XML with XStream

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