Develop Reference

JAXB, XSD stylesheets, and element name conflict resolution

This is more of an academic question, but I started working on configuring JAXB schema validation because I was researching what would happen using more than one schema with an element name conflict. Is it possible to configure JAXB and have schema files which support an XML document which looks something like this?
<my:inventory
xmlns:my="http://www.my.com"
xmlns:ab="http://www.ab.com"
xmlns:xy="http://www.xy.com">
<my:products>
<ab:product>
<id>123</id>
<desc>some ap product</desc>
<price>12.22</price>
</ab:product>
<xy:product>
<key>123</key>
<title>some xy product</title>
<cost>63.45</cost>
</xy:product>
</my:products>
</my:inventory>
The basic idea is to have product information from both AB company and XY company. The two companies have the same data but store them in different tags. I would like to have MY company schema to define an inventory of products from the two other companies.
I started to create the XSD files and the JAXB annotated classes for this. It quickly spiraled into an unending stream of configuration and parsing exceptions, so I thought I'd ask.

Yes it is possible to have JAXB support XML documents with more than one namespace. You end up with something like the following:
#XmlAccessorType(XmlAccessType.FIELD)
public class Products {
#XmlElement(name="product", namespace="http://www.ab.com")
private Product product1;
#XmlElement(name="product", namespace="http://www.xy.com")
private Product product2;
}
For More Information
I have written more about JAXB and namespaces on my blog:
http://blog.bdoughan.com/2010/08/jaxb-namespaces.html

How to map an XML to Java objects by XPaths?

Given the XML example:
<fooRoot>
<bar>
<lol>LOLOLOLOL</lol>
</bar>
<noob>
<boon>
<thisIsIt></thisIsIt>
</boon>
</noob>
</fooRoot>
Which should be mapped to:
class MyFoo {
String lol;
String thisIsIt;
Object somethingUnrelated;
}
Constraints:
XML should not be transformed, it is provided as a parsed org.w3c.dom.Document object.
Class does not and will not map 1:1 to the XML.
I'm only interested to map specific paths of the XML to specific fields of the object.
My dream solution would look like:
#XmlMapped
class MyFoo {
#XmlElement("/fooRoot/bar/lol")
String lol;
#XmlElement("/noob/boon/thisIsIt")
String thisIsIt;
#XmlIgnore
Object somethingUnrelated;
}
Does anything likewise exists? What I've found either required a strict 1:1 mapping (e.g. JMX, JAXB) or manual iteration over all fields (e.g. SAX, Commons Digester.)
JiBX binding definitions come the nearest to what I'm lokking for. However, this tool is ment to marshall/unmarshall complete hierarchy of Java objects. I only would like to extract parts of an XML document into an existing Java bean at runtime.

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB 2 (JSR-222) expert group.
You can do this with MOXy:
#XmlRootElement(name="fooRoot")
class MyFoo {
#XmlPath("bar/lol/text()")
String lol;
#XmlElement("noob/boon/thisIsIt/text()")
String thisIsIt;
#XmlTransient
Object somethingUnrelated;
}
For More Information
http://blog.bdoughan.com/2010/07/xpath-based-mapping.html
http://blog.bdoughan.com/2010/09/xpath-based-mapping-geocode-example.html
http://blog.bdoughan.com/2011/03/map-to-element-based-on-attribute-value.html
http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html

Try XStream. It's super easy. Hope it helps! I don't have time now for a full example :)

One option could be write a custom annotation which will take the XPath expression as input and do the bindings.

How to detect required XML attributes?

I have an XML content without defined attributes, like this:
<rootElement>
<subElement1/>
</rootElement>
I want to populate this XML content with required attributes defined in XML Schema (XSD) for this XML.
For example, according to XSD subElement1 has required attribute 'id'.
What is the best way (for Java processing) to detect that and add such attributes to XML?
We need to add required attributes and set appropriate values for them.
As a result for example above we need to have the following XML:
<rootElement>
<subElement1 id="some-value"/>
</rootElement>

In the XML schema definition, i.e. XSD file, attributes are optional by default. To make an attribute required, you have to define:
<xs:attribute name="surname" type="xs:string" use="required"/>
You will find a very good introduction on XML and XML Schema Definitions, i.e. XSD, on W3 Schools.
In Java the equivalent of defining a XML schema is using JAXB, i.e. Java API for XML Binding that is included into Java SE. There you would define, e.g.
#XmlRootElement
public class Person { public #XmlAttribute(required=true) String surname; }
Hope this could clarify your question.

I would suggest you to use JAXB for that. Search the Internet for tutorials.
Steps to proceed further with JAXB,
Generate Java files using JAXB by providing the schema
Unmarshal your XML to generated Java classes (beans). Don't do validation or set validation handler here.
Populate those classes with appropriate values. required elements can be found using annotation look up. JAXB annotation for element would look like something, #XmlElement(name = "ElementName", required = true). And an attribute annotation would be something similar to this, #XmlAttribute(required = true)
Marshal your bean back to XML. You can validate your bean using ValidationHandler, while marshalling. Below is the sample code snippet,
marshller = JAXBContext.newInstance(pkgOrClassName).createUnmarshaller();
marshller.setSchema(getSchema(xsd)); // skip this line for unmarshaller
marshller.setEventHandler(new ValidationHandler()); // skip this line for unmarshaller

Use a DOM parser.Has methods to traverse XML trees, access, insert, and delete nodes

I have had the same idea of Cris but I think that with this validator you don't have information about the point in which you have had the error.
I think that you have to create or extend your own validator.

XSD design issues in Java

Currently our software is interacting with a remote web service via XML/SOAP. We're using XSDs to conveniently create the requests to be sent to the remote system. That's fine, and it's working well. XSD is pretty awesome.
However, it does lead to very lengthy code blocks for creating the Document objects. I'm wondering if anyone has suggestions for good design practices to handle these large code blocks for creation of the request and handling of the response Documents.
The point of the XSD Document object is to decouple the XML creation from the client. However, I'm thinking a facade class might be a good idea for each service. I think this would be great for creation, since the facade class could be given the ingredients to build the request document, and send the request, without coupling the client to the XSD classes. I think a problem arises in the response Documents. If there is a multi-level response, you'll end up creating POJO classes just to wrap the XSD classes, which seems like over-kill.

Note: I'm the EclipseLink JAXB (MOXy) tech lead.
EclipseLink JAXB (MOXy)
MOXy is a JAXB (JSR-222) implementation that has an XPath based mapping extension. This means you can map a more compact object model to your XML. In the example below a simple Address object is mapped to Google's Geocoding V2 format:
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import org.eclipse.persistence.oxm.annotations.XmlPath;
#XmlRootElement(name="kml")
#XmlType(propOrder={"country", "state", "city", "street", "postalCode"})
public class Address {
#XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:SubAdministrativeArea/ns:Locality/ns:Thoroughfare/ns:ThoroughfareName/text()")
private String street;
#XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:SubAdministrativeArea/ns:Locality/ns:LocalityName/text()")
private String city;
#XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:AdministrativeAreaName/text()")
private String state;
#XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:CountryNameCode/text()")
private String country;
#XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:SubAdministrativeArea/ns:Locality/ns:PostalCode/ns:PostalCodeNumber/text()")
private String postalCode;
}
The above class corresponds to the following XML:
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://earth.google.com/kml/2.0" xmlns:ns="urn:oasis:names:tc:ciq:xsdschema:xAL:2.0">
<Response>
<Placemark>
<ns:AddressDetails>
<ns:Country>
<ns:CountryNameCode>US</ns:CountryNameCode>
<ns:AdministrativeArea>
<ns:AdministrativeAreaName>CA</ns:AdministrativeAreaName>
<ns:SubAdministrativeArea>
<ns:Locality>
<ns:LocalityName>Mountain View</ns:LocalityName>
<ns:Thoroughfare>
<ns:ThoroughfareName>1600 Amphitheatre Pkwy</ns:ThoroughfareName>
</ns:Thoroughfare>
<ns:PostalCode>
<ns:PostalCodeNumber>94043</ns:PostalCodeNumber>
</ns:PostalCode>
</ns:Locality>
</ns:SubAdministrativeArea>
</ns:AdministrativeArea>
</ns:Country>
</ns:AddressDetails>
</Placemark>
</Response>
</kml>
For More Information
XPath Based Mapping - Geocode Example
Map to Element based on an Attribute Value with EclipseLink JAXB (MOXy)
XPath Based Mapping

parse google geocode with xstream

I'm using Java and XStream to parse a google geocode request over http. My idea is to have an Address class with all the geocode attr's (ie. lat/long, city, provice/state etc) but I'm having problems parsing the xml with xstream.
The google response is similar to this:
<?xml version="1.0" encoding="UTF-8" ?>
<kml xmlns="http://earth.google.com/kml/2.0"><Response>
<name>98 St. Patrick St, Toronto</name>
<Status>
<code>200</code>
<request>geocode</request>
</Status>
<Placemark id="p1">
<address>98 St Patrick St, Toronto, ON, Canada</address>
<AddressDetails Accuracy="8" xmlns="urn:oasis:names:tc:ciq:xsdschema:xAL:2.0"> <Country><CountryNameCode>CA</CountryNameCode><CountryName>Canada</CountryName><AdministrativeArea><AdministrativeAreaName>ON</AdministrativeAreaName><Locality><LocalityName>Toronto</LocalityName><Thoroughfare><ThoroughfareName>98 St Patrick St</ThoroughfareName></Thoroughfare><PostalCode><PostalCodeNumber>M5T</PostalCodeNumber></PostalCode></Locality></AdministrativeArea></Country></AddressDetails>
<ExtendedData>
<LatLonBox north="43.6560378" south="43.6497426" east="-79.3864912" west="-79.3927864" />
</ExtendedData>
<Point><coordinates>-79.3896388,43.6528902,0</coordinates></Point>
</Placemark>
</Response></kml>
That doesn't show up very well, but the meat of the code is in the AddressDetails tag.
Anyway, I'm new to Java and XStream so the API terminology is a bit confusing for me. I just need to be able to write some mapper that maps all these tags (ie. CountryName) to an attribute within my Address object, (ie. address.country = blah) The address object will be pretty simple, mainly just strings for country name etc and floats for lat/long.
The docs and example just show straight mapping where each xml tag maps directly to the attribute of the same name of the object. In my case however, the tags are named different than the object attr's. A quick point in the right direction is all I'm looking for really.

I've used XStream in several projects. Unfortunately, your problem isn't really what XStream is designed to solve. You might be able to use its converter mechanism to achieve your immediate goal, but you'll run into limitations. In a nutshell, XStream isn't designed to do conversion of Tree Structure A into Tree Structure B -- it's purpose is to convert from a Java domain model into some reasonable XML. XStream is a great tool when you don't care much about the details of the XML produced. If you care more about the XML than the Java objects, look at XMLBeans -- the Java is ugly, but it's incredibly schema-compliant.
For your project, I'd run the Google XML schema through XML beans, generate some Java that will give you a more literate way of hand-coding a converter. You could use a raw DOM tree, but you'd have code like myAddress.setStreet(root.getFirstChild().getAttribute("addr1"))). With XML beans, you say things like myAddress.setStreet(googleResult.getAddress().getStreetName();
I'd ignore JAXB as it's attempt to separate interface from implementation adds needless complexity. Castor might be a good tool to consider as well, but I haven't used it in years.
In a nutshell, there aren't a lot of good Object-to-Object or XML-to-Object converters that handle structure conversion well. Of those I've seen that attempt declarative solutions, all of them seemed much more complicated (and no more maintainable) than using XStream/XmlBeans along with hand-coded structure conversions.

Would it be possible to define a separate class specifically for dealing with XStream's mapping? You could then simply populate your AddressDetails object by querying values out of this other object.

I've ended up just using xpath and populating my own address object manually. Seems to work fine.

Have you tried with json format? It should be the same but you'll need to set a com.thoughtworks.xstream.io.json.JettisonMappedXmlDriver as the driver for XStream

You could use EclipseLink JAXB (MOXy) to do this:
package com.example;
import javax.xml.bind.annotation.XmlRootElement;
import org.eclipse.persistence.oxm.annotations.XmlPath;
#XmlRootElement(name="kml")
public class Address {
private String country;
#XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:CountryName/text()")
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
}
and
#javax.xml.bind.annotation.XmlSchema(
namespace = "http://earth.google.com/kml/2.0",
xmlns = {
#javax.xml.bind.annotation.XmlNs(
prefix = "ns", namespaceURI ="urn:oasis:names:tc:ciq:xsdschema:xAL:2.0")
},
elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED)
package com.example;
A full example is available here:
http://bdoughan.blogspot.com/2010/09/xpath-based-mapping-geocode-example.html