Hi John,
js wrote:
> hi,
>
> I'll eventually figure this out, but i have been struggling for at least 2
> days trying to unmarshall the simplest xml.. i must really be getting
> frustrated if i resorted to emailing the open source developers.. anyway:
>
> all i want to do is unmarshall a simple xml file involving nested
> collections
>
> <persons>
> <person><name>billy</name>
> <address>
> <address1>West St.</address1>
> </address>
> <address>
> <address1>East St.<address1>
> </address>
> </person>
> <person><name>bob</name>
> <address>
> <address1>North St.</address1>
> </address>
> <address>
> <address1>South St.<address1>
> </address>
> </person>
> </persons>
>
>
> i have tried all the examples at codehaus (which are all
> marshall-centric).
Well, no. Not really. See, XStream is about Java object to XML *and back*,
i.e. every example can also unmarshal.
> i have googled countless sites.
> no where have i found a simple, complete example that does this most basic
> of requirements.
Because it's not necessary? ... see below ;-)
> if collections are created, they are either null or empty.
> Lots of: No field "person" for implicit collection errors as well.
>
> ====== CODE =========
>
> public class Persons {
>
> private List<Person> persons = new ArrayList<Person>();
>
> public List<Person> getPersons() {
> return persons;
> }
> public void setPersons(List<Person> persons) {
> this.persons = persons;
> }
>
> }
> //this is a "command" class as one does not need a model class for
> "persons" thus the List instead of Set (i was just following examples i
> found online, but would rather it be a set as well).
You may also use directly an array (Person[]).
> //also, why examples have get() and add(), instead of POJO get(), set()?
Why do you think the objects have to be POJOs?
> ---------
>
> public class Person {
>
> private String name;
> private Set<Address> addresses = new HashSet<Address>();
>
> public String getName() {
> return name;
> }
> public void setName(String name) {
> this.name = name;
> }
>
>
> public Set<Address> getAddresses() {
> return addresses;
> }
> public void setAddresses(Set<Address> addresses) {
> this.addresses = addresses;
> }
> }
>
> //are complete constructors required?
Neither constructors nor setters are required.
> -------------
>
> public class Address {
>
> private String address1;
>
> public String getAddress1() {
> return address1;
> }
> public void setAddress1(String address1) {
> this.address1 = address1;
> }
>
> }
>
> --------------
>
> public void personsFromXML(MultipartFile xml) {
> XStream xstream = new XStream(new StaxDriver());
> Persons persons = new Persons();
> xstream.alias("persons", Persons.class);
>
> try {
> persons = (Persons)xstream.fromXML(xml.getInputStream());
>
> }
> catch(Exception e){
> e.printStackTrace();
> }
>
> --------------
>
> i have tried annotations in Persons.class as well as all variations of the
> below (+ others):
> //xstream.addImplicitCollection(Person.class, "person");
> //xstream.alias("persons", Persons.class);
> //xstream.alias("person", Person.class);
> //xstream.alias("address", Address.class);
> //xstream.addImplicitCollection(Person.class, "person");
> //xstream.addImplicitCollection(Person.class, "person",
> Persons.class);
> //xstream.addImplicitCollection(Persons.class, "person",
> Person.class);
http://xstream.codehaus.org/faq.html#XML_unmarshalling_fails
Therefore adjust the marshalling. If XStream generates the required XML
format, it can also read it. It is a very tedious and annoying task to try
it the other way round (you already found this out), because you never know
- especially as starter - why XStream throws an exception or silently skips
some elements.
> how does xstream know that collection A is within Persons.class, but
> collection B is in Person.class?
Java reflection.
> are the generic converters being used when xtream performs its
> auto-deserialization magic?
Since XStream has obviously no built-in converters for Person or Address, it
has to use the generic converters (based on reflection).
> are aliases and implicitCollections handled diff when marshall v.
> unmarshall?
No. That's the point. Adjust the XStream and write an object as XML and you
will see immediately what has been influenced.
Hope this helps,
Jörg
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