JAXB and Package Level XmlAdapters

The XmlAdapter mechanism in JAXB (JSR-222) allows an unmappable class to be converted to a mappable one.  An XmlAdapter can be registered with the @XmlJavaTypeAdapter at the field, property, type, or package level.  This post will focus on the scope of the XmlAdapter when registered at the package level.


Package 1 - xmladapter.bar

package-info

When an XmlAdapter is registered at the package level it must include the type parameter.  The type parameter specifies the Java class that this XmlAdapter will be applied to.  For this package (xmladapter.bar) we will specify an XmlAdapter (StringAdapter) that will be applied to all fields/properties of type String within this package.

@XmlJavaTypeAdapters({
    @XmlJavaTypeAdapter(value=StringAdapter.class, type=String.class)
})
package xmladapter.bar;

import javax.xml.bind.annotation.adapters.*; 

StringAdapter

Our XmlAdapter will simply convert all instances of String to upper case when marshalling:

package xmladapter.bar;

import javax.xml.bind.annotation.adapters.XmlAdapter;

public class StringAdapter extends XmlAdapter<String, String> {

    @Override
    public String unmarshal(String v) throws Exception {
        return v;
    }

    @Override
    public String marshal(String v) throws Exception {
        if(null == v) {
            return v;
        }
        return v.toUpperCase();
    }

}

Bar

Bar represents a POJO in this package with a property (name) of type String:

package xmladapter.bar;

public class Bar {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

Package 2 - xmladapter.foo

Foo

Foo represents a domain object with a property of type String that exists in a different package (xmladapter.foo). The XmlAdapter we registered for the xmladapter.bar package will not apply to String fields/properties on this class:

package xmladapter.foo;

import javax.xml.bind.annotation.*;
import xmladapter.bar.Bar;

@XmlRootElement
@XmlType(propOrder={"name", "bar"})
public class Foo {

    private String name;
    private Bar bar;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Bar getBar() {
        return bar;
    }

    public void setBar(Bar bar) {
        this.bar = bar;
    }

}

Demo

The following code will create instances of both Foo and Bar and marshal them to XML.  Note how the values set on the name properties for both Foo and Bar are lower case:

package xmladapter;

import javax.xml.bind.*;
import xmladapter.bar.Bar;
import xmladapter.foo.Foo;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Foo.class, Bar.class);
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

        Foo foo = new Foo();
        foo.setName("foo");

        Bar bar = new Bar();
        bar.setName("bar");
        foo.setBar(bar);
 
        marshaller.marshal(foo, System.out);
    }

}

Output

Notice how the value of the name element within bar has been converted to upper case (line 5), but he name element within foo has not (line 3):

<?xml version="1.0" encoding="UTF-8"?>
<foo>
    <name>foo</name>
    <bar>
        <name>BAR</name>
    </bar>
</foo>

Further Reading

If you enjoyed this post then you may also be interested in:

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