Mapping Objects to Multiple XML Schemas - Weather Example
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Join For FreeI have written previous posts on EclipseLink JAXB (MOXy)'s @XmlPath and external binding file
extensions. In this post I will demonstrate how powerful these
extensions are by mapping a single object model to two different XML
schemas. To make the example more "real", the XML data will come from
two different services that provide weather information: Google and
Yahoo.
Java Model
Weather Report
package blog.weather;
import java.util.List;
public class WeatherReport {
private String location;
private int currentTemperature;
private String currentCondition;
private List<Forecast> forecast;
}
Forecast
package blog.weather;
public class Forecast {
private String dayOfTheWeek;
private int low;
private int high;
private String condition;
}Google Weather API
First we will leverage Google's Weather API. The following URL will be used to access the weather data for Ottawa, Canada:
The following is the result of performing the above query at time I was writing this article. I have highlighted the portions of the XML document that we will map to:
Java Model - Mapped to Google's XML Schema via Annotations
We will map the result of the Google weather API via a combination of standard JAXB and MOXy extension annotations.
Weather Report
package blog.weather;
import java.util.List;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import org.eclipse.persistence.oxm.annotations.XmlPath;
@XmlRootElement(name="xml_api_reply")
@XmlType(propOrder={"location", "currentCondition", "currentTemperature", "forecast"})
@XmlAccessorType(XmlAccessType.FIELD)
public class WeatherReport {
@XmlPath("weather/forecast_information/city/@data")
private String location;
@XmlPath("weather/current_conditions/temp_f/@data")
private int currentTemperature;
@XmlPath("weather/current_conditions/condition/@data")
private String currentCondition;
@XmlPath("weather/forecast_conditions")
private List<Forecast> forecast;
}Forecast
package blog.weather;
import org.eclipse.persistence.oxm.annotations.XmlPath;
public class Forecast {
@XmlPath("day_of_week/@data")
private String dayOfTheWeek;
@XmlPath("low/@data")
private int low;
@XmlPath("high/@data")
private int high;
@XmlPath("condition/@data")
private String condition;
}Specify MOXy as the JAXB Provider (jaxb.properties)
To configure MOXy as your JAXB provider simply add a file named jaxb.properties in the same package as your domain model with the following entry:
javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory
For more information see: Specifying EclipseLink MOXy as Your JAXB Provider.
Demo
The following demo code will read the XML data for Google's weather service, and marshal the objects back to XML:
package blog.weather;
import java.net.URL;
import javax.xml.bind.*;
public class GoogleDemo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(WeatherReport.class);
Unmarshaller unmarshaller = jc.createUnmarshaller();
URL url = new URL("http://www.google.com/ig/api?weather=Ottawa");
WeatherReport weatherReport = (WeatherReport) unmarshaller.unmarshal(url);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(weatherReport, System.out);
}
}
Output
Yahoo Weather API
The following URL will be used to access the weather data for Ottawa using the Yahoo Weather API (3369 is the WOEID for Ottawa):
The following is the result of performing the above query at time I was writing this article:
Java Model - Mapped to Yahoo's XML Schema via XML Metadata
<?xml version="1.0"?>
<xml-bindings
xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
package-name="blog.weather"
xml-mapping-metadata-complete="true">
<xml-schema element-form-default="QUALIFIED">
<xml-ns prefix="yweather" namespace-uri="http://xml.weather.yahoo.com/ns/rss/1.0"/>
</xml-schema>
<java-types>
<java-type name="WeatherReport" xml-accessor-type="FIELD">
<xml-root-element name="rss"/>
<xml-type prop-order="location currentTemperature currentCondition forecast"/>
<java-attributes>
<xml-attribute java-attribute="location" xml-path="channel/yweather:location/@city"/>
<xml-attribute java-attribute="currentTemperature" name="channel/item/yweather:condition/@temp"/>
<xml-attribute java-attribute="currentCondition" name="channel/item/yweather:condition/@text"/>
<xml-element java-attribute="forecast" name="channel/item/yweather:forecast"/>
</java-attributes>
</java-type>
<java-type name="Forecast" xml-accessor-type="FIELD">
<java-attributes>
<xml-attribute java-attribute="dayOfTheWeek" name="day"/>
<xml-attribute java-attribute="low"/>
<xml-attribute java-attribute="high"/>
<xml-attribute java-attribute="condition" name="text"/>
</java-attributes>
</java-type>
</java-types>
</xml-bindings>Demo
The following demo code will read the XML data for Yahoo's weather service, and marshal the objects back to XML. Due to a MOXy bug regarding unmapped CDATA sections (https://bugs.eclipse.org/357145, this bug has been fixed in EclipseLink 2.3.1), a filtered XMLStreamReader was used to remove it from the XML input:
package blog.weather;
import java.util.HashMap;
import java.util.Map;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.StreamFilter;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamReader;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.JAXBContextFactory;
public class YahooDemo {
public static void main(String[] args) throws Exception {
Map<String, Object> properties = new HashMap<String, Object>(1);
properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, "blog/weather/yahoo-binding.xml");
JAXBContext jc = JAXBContext.newInstance(new Class[] {WeatherReport.class}, properties);
XMLInputFactory xif = XMLInputFactory.newFactory();
StreamSource xml = new StreamSource("http://weather.yahooapis.com/forecastrss?w=3369");
XMLStreamReader xsr = xif.createXMLStreamReader(xml);
xsr = xif.createFilteredReader(xsr, new CDATAFilter());
Unmarshaller unmarshaller = jc.createUnmarshaller();
WeatherReport weatherReport = (WeatherReport) unmarshaller.unmarshal(xsr);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(weatherReport, System.out);
}
private static class CDATAFilter implements StreamFilter {
public boolean accept(XMLStreamReader xsr) {
return XMLStreamReader.CDATA != xsr.getEventType();
}
}
}
Output
Below is the result of running the demo code. The output represents the portion of the XML document that we had mapped to:
<?xml version="1.0" encoding="UTF-8"?>
<rss xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0">
<channel>
<yweather:location city="Ottawa"/>
<item>
<yweather:forecast day="Thu" low="57" high="74" text="Partly Cloudy"/>
<yweather:forecast day="Fri" low="53" high="79" text="Partly Cloudy"/>
</item>
</channel>
</rss>
From http://blog.bdoughan.com/2011/09/mapping-objects-to-multiple-xml-schemas.html
XML
Object (computer science)
Schema
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