convert javaobjects to xml and xml to java objects dynamically

hi,
i have a class called Converter which needs to do 4 things.
1) It will receive a xml file .this xml file i need to convert to a object with the datas in the xml stored in the object.
for ex.
if i get a xml file like say
foo.xml[this xml file will change]
<mail>
<to>raj@yahoo.com</to>
<from>kishore@hotmail.com</from>
<subject>Hello Raj</subject>
<message>Have a nice time</message>
</mail>
now this xml files data between the markups must be initialized in a java object. and that object which is initialized must be returned by my class.
2) i will receive a object which has been initialized with data . now i need to read the data in the object and write them to a xml file.
3) i will receive a xml string representing some content in it to my class , this xml string needs to be read and its data need to be written to an object.[note: we can assume the content to be the data between the tags in the above xml file]
4) i will receive an object , to which my class Converter must read its content and return a xml string with the objects content.this xml string i need to return from my class.
My question is what xml parser should i use , jaxb or castor have given examples which are static in the sense that they advocate getter and setter methods which are based on the xml file. but the xml file i get could contain any structure, so i need a parser which would fix my problem dynamically. in future i need to parse a xml schema file also .so pl take that into consideration and recommend a xml parser which will convert xml file / schema to java objects and vice versa.this looks tough for me as i am new to databinding and xml.Any recommendations will be helpful.
Thanks in advance.
Kiranmanohar

How about just reading the XML into a DOM tree and implementing the conversion manually? I haven't had much experience with binding products such as JAXB or Castor so I cannot say whether they would be helpful in this kind of generic binding.

i am new to xml& java databinding , u had mentioned about reading the xml in a dom tree
could u give me few examples to get me started.
Thanks in advance
Kiranmanohar

Here's a good example of how to use the DocumentBuilder utility for parsing an XML file into an org.w3c.dom.Document object.

after parsing the xml file how to use the Document object to initialize my object.thanks for ur help Lasse.

You traverse through the DOM tree, pick element values where appropriate, and call setThisAndThat("...") on your domain object.
Here's a very simple example:

private ArrayList convertDocumentIntoDomainObjects(Document doc) {
        ArrayList domainObjects = new ArrayList();
        Element root = doc.getDocumentElement();
        NodeList agentElements = root.getChildNodes();
        for (int i=0; i < agentElements.getLength(); i++) {
            Node agentElement = agentElements.item(i);
            if (agentElement.getNodeType() != Node.ELEMENT_NODE) {
                // ignoring element due to wrong node type
                continue;
            }
            
            String name = agentElement.getNodeName();
            if (name != null && name.equals("agent")) {
                domainObjects.add(convertAgentElementIntoObject((Element)agentElement));
            }
        }
        
        return domainObjects;
    }
    /**
     * Converts a given <agent> element into an Agent object.
     */
    private Agent convertAgentElementIntoObject(Element agentElement) {
        Agent agent = new Agent();
        agent.setName(agentElement.getAttribute("name"));
        agent.setIataNumber(agentElement.getAttribute("iatanumber"));
        return agent;
    }

Thanks Lasse,
Ur coding is working. But the coding is not generic i presume. that is if i want to send any xml file and parse it to java objects how to go about it
Regards
Kiranmanohar

lasse,
i have a doubt . u said that DOM is to be used in the coding. my doubt is would it parse an xml schema as well as a xml file and also a xml string.
that is a string object holding xml tags in it.
Thanks
Regards
Kiranmanohar

that is if i want to send any xml file and parse it to java objects how to go about it

Either you need to implement your own Java-to-XML mapping or use an existing XML data binding API such as Sun's JAXB or Castor.

u said that DOM is to be used in the coding. my doubt is would it parse an xml schema as well as a xml file and also a xml string.
that is a string object holding xml tags in it.

Could you rephrase this 'cause I didn't quite get what you're asking?

By the way, the DOM tree generated by a DOM parser is as generic a Java object representation of your arbitrary XML document as possible...

JAXB generates objects for a specific schema , so they are not generic.

There's an open source package called skaringa that does objects -> xml -> objects that does what you want.
http://skaringa.sourceforge.net/
I built myself a handy little wrapper around it and I use it like

http://skaringa.sourceforge.net/

Thanks! I had somehow forgotten Skaringa completely.

thanks lasse
for the skaringa links, but for now i will continue with DOM.in the coding for dom u have used Agent . in which package does this Agent Class or Interface is used and how to add it. i m using jdk1.4 by the way.
Regards
Kiranmanohar