xstream.fromXML returns a Class

Question

Using XStream 1.2.2

The XML document:

<?xml version="1.0" encoding="ISO-8859-1"?>
<Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" protocol="OCI" xmlns="C">  
<sessionId xmlns="">192.168.1.19,299365097130,1517884537</sessionId>  
  <command xsi:type="AuthenticationRequest" xmlns="">    
    <userId>me@somewhere.com</userId>  
  </command>
</Document>

I'm trying to parse into to a Document;

public class Document {
    private String sessionId;
    public Command command;
    public Command getCommand() {
        return this.command;
    }
    public void setCommand(Command command) {
        this.command = command;
    }
    public String getSessionId() {
        return sessionId;
    }
    public void setSessionId(String sessionId) {
        this.sessionId = sessionId;
    }
}

Parsing code is:

    XStream xstream = new XStream();
    xstream.alias("Document", Document.class);
    xstream.alias("sessionId", String.class);
    xstream.alias("command", Command.class);
    xstream.alias("userId", String.class);

    Document doc = (Document) xstream.fromXML(theInput, Document.class);

but this throws:

java.lang.ClassCastException: java.lang.Class cannot be cast to com.mycompany.ocip.server.model.Document

because the returned object from fromXml is of type: Class<com.mycompany.ocip.server.model.Document>

Shouldn't I expect it to return a com.mycompany.ocip.server.model.Document instance?

Answer 1

That needs to be:

Document doc = (Document) xstream.fromXML(theInput);

If you pass in a second parameter, XStream will try to populate that with the values from the XML. Since in your code, you're passing in a class object, XStream will try to populate the class object and return it.

The JavaDoc has the details.