JAXB Jackson - How to handle maps? - rest

Question

I have an web application in which I generate POJOs from my domain objects. One of my domain objects contain a map and JAXB generates the following schema:
<xs:element name="persons">
<xs:complexType>
<xs:sequence>
<xs:element name="entry" minOccurs="0" maxOccurs="unbounded">
<xs:complexType>
<xs:sequence>
<xs:element name="key" minOccurs="0" type="xs:string"/>
<xs:element name="value" minOccurs="0" type="person"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
This is generated from HashMap<String, Person> persons:
#XmlAccessorType(XmlAccessType.FIELD)
#XmlType(name = "personConfiguration", propOrder = {
"persons",
})
#XmlRootElement(name = "personConfiguration")
public class PersonConfiguration
{
#XmlElement(required = true)
protected PersonConfiguration.Persons persons;
/**
* Gets the value of the persons property.
*
* #return
* possible object is
* {#link PersonConfiguration.Persons }
*
*/
public PersonConfiguration.Persons getPersons() {
return persons;
}
/**
* Sets the value of the persons property.
*
* #param value
* allowed object is
* {#link PersonConfiguration.Persons }
*
*/
public void setPersons(PersonConfiguration.Persons value) {
this.persons = value;
}
#XmlAccessorType(XmlAccessType.FIELD)
#XmlType(name = "", propOrder = {
"entry"
})
public static class Persons
{
protected List<PersonConfiguration.Persons.Entry> entry;
/**
* Gets the value of the entry property.
*
* <p>
* This accessor method returns a reference to the live list,
* not a snapshot. Therefore any modification you make to the
* returned list will be present inside the JAXB object.
* This is why there is not a <CODE>set</CODE> method for the entry property.
*
* <p>
* For example, to add a new item, do as follows:
* <pre>
* getEntry().add(newItem);
* </pre>
*
*
* <p>
* Objects of the following type(s) are allowed in the list
* {#link PersonConfiguration.Persons.Entry }
*
*
*/
public List<PersonConfiguration.Persons.Entry> getEntry() {
if (entry == null) {
entry = new ArrayList<PersonConfiguration.Persons.Entry>();
}
return this.entry;
}
#XmlAccessorType(XmlAccessType.FIELD)
#XmlType(name = "", propOrder = {
"key",
"value"
})
public static class Entry
{
protected String key;
protected Person value;
/**
* Gets the value of the key property.
*
* #return
* possible object is
* {#link String }
*
*/
public String getKey() {
return key;
}
/**
* Sets the value of the key property.
*
* #param value
* allowed object is
* {#link String }
*
*/
public void setKey(String value) {
this.key = value;
}
/**
* Gets the value of the value property.
*
* #return
* possible object is
* {#link Person }
*
*/
public Person getValue() {
return value;
}
/**
* Sets the value of the value property.
*
* #param value
* allowed object is
* {#link Person }
*
*/
public void setValue(Person value) {
this.value = value;
}
}
}
}
As one can see JAXB added this extra level of indirection entry -> key, value. Other pieces of the puzzle are Spring MVC, REST call using JSON objects.
Now XML based REST Calls work fine with object schema above but when send the same call with JSON message with the same schema I get a JSONMappingException.
Any ideas of why this might be happening?

Answer 1

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.
When using different XML and JSON-binding providers it is difficult to keep the XML and JSON representations consistent. Below is and example of how this can be simplified using MOXy as both your XML and JSON provider with all mapping information provided as JAXB annotations.
Root
Below is a sample domain object in which the persons field would generate the XML schema fragment from your question.
package forum13784163;
import java.util.Map;
import javax.xml.bind.annotation.*;
#XmlRootElement
#XmlAccessorType(XmlAccessType.FIELD)
public class Root {
Map<String, Person> persons;
}
Person
Below is a sample of what your Person class might look like. Note how I have mapped the id field to an XML attribute.
package forum13784163;
import javax.xml.bind.annotation.*;
#XmlAccessorType(XmlAccessType.FIELD)
public class Person {
#XmlAttribute
int id;
String name;
int age;
}
jaxb.properties
To use MOXy as your JAXB provider you need to include a file called jaxb.properties in the same package as your domain model with the following entry (see: http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html).
javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory
input.json
Below is what the JSON representation would look like if MOXy is used as your JSON binding provider.
{
"persons" : {
"entry" : [ {
"key" : "Jane",
"value" : {
"id" : 123,
"name" : "Jane",
"age" : 30
}
} ]
}
}
Demo
In the demo code below the JSON is unmarshalled into objects and then those same objects are marshalled to XML. This is done from one JAXBContext that contains one set of metadata.
package forum13784163;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.UnmarshallerProperties;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(Root.class);
Unmarshaller unmarshaller = jc.createUnmarshaller();
unmarshaller.setProperty(UnmarshallerProperties.MEDIA_TYPE, "application/json");
unmarshaller.setProperty(UnmarshallerProperties.JSON_INCLUDE_ROOT, false);
StreamSource json = new StreamSource("src/forum13784163/input.json");
Root root = unmarshaller.unmarshal(json, Root.class).getValue();
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(root, System.out);
}
}
Output
Below is the resulting XML.
<?xml version="1.0" encoding="UTF-8"?>
<root>
<persons>
<entry>
<key>Jane</key>
<value id="123">
<name>Jane</name>
<age>30</age>
</value>
</entry>
</persons>
</root>
For More Information
http://blog.bdoughan.com/2012/05/moxy-as-your-jax-rs-json-provider.html