Latest revision as of 11:36, 18 June 2012

XML Location

In the current JAXB RI, developed by Sun, there is a series of "proprietary" JAXB extensions which provide advanced functionality outside of the JAXB specification (these extension classes and properties reside in the com.sun.xml.bind package).

The @XmlLocation annotation is one of these extensions - it allows the user to specify a property on the JAXB object that will be updated (upon unmarshalling) with that object's XML location information (i.e. the line number, column number, and system ID that points to this object's location in the XML input).

Behaviour

If an object containing an @XmlLocation property is unmarshalled, a Locator object will be created and set on the property, containing the XML location info.

Not all unmarshal sources will be able to provide XML location information. For example, unmarshalling from a File would be able to give you line, column and system ID (filename); system ID is not available when unmarshalling from an InputStream; unmarshalling from a Node would give you no XML location information at all.

Unmarshal Source	Line #	Column #	System ID
java.io.File
java.io.InputStream
java.io.Reader
java.net.URL
javax.xml.stream.XMLEventReader
javax.xml.stream.XMLStreamReader
org.w3c.dom.Node
org.xml.sax.InputSource

Configuration

In order to use @XmlLocation, the user must first have a property on their Java object (either a field or get/set pair) of type org.xml.sax.Locator. The user can then specify that this property should be used to track XML location by using either EclipseLink Annotations or XML Bindings.

Properties marked with @XmlLocation should also be marked as @XmlTransient, as the location information is not relevant in a marshalled document.

EclipseLink will also recognize the Sun versions of this annotation (com.sun.xml.bind.annotation.XmlLocation and com.sun.xml.internal.bind.annotation.XmlLocation).

Annotations

package org.eclipse.persistence.oxm.annotations;
 
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
 
@Target({METHOD, FIELD}) 
@Retention(RUNTIME)
public @interface XmlLocation {}

XML Bindings

eclipselink_oxm_2_4.xsd:

...
    <xs:element name="xml-transient" substitutionGroup="java-attribute">
        <xs:complexType>
            <xs:complexContent>
                <xs:extension base="java-attribute">
                    <xs:attribute name="xml-location" type="xs:boolean" default="false" />
                </xs:extension>
            </xs:complexContent>
        </xs:complexType>
    </xs:element>
...
    <xs:element name="xml-element" substitutionGroup="java-attribute">
        <xs:complexType>
            <xs:complexContent>
                <xs:extension base="java-attribute">
                    ...
                    <xs:attribute name="xml-location" type="xs:boolean" default="false" />
                </xs:extension>
            </xs:complexContent>
        </xs:complexType>
    </xs:element>
...

Config Options

The @XmlLocation feature does not expose any configuration options, it is merely a tagging annotation that indicates the property to be used for tracking XML location information.

Examples

The following examples refer to this XML instance document:

<?xml version="1.0" encoding="UTF-8"?>
<customer>
   <id>1872874</id>
   <name>Bob Smith</name>
</customer>

Example 1

This example shows the most basic use case; the Locator field is annotated with @XmlLocation (or, in XML Bindings, the "xml-transient" element has its "xml-location" attribute set to "true").

Annotations:

import javax.xml.bind.annotation.*;
 
import org.eclipse.persistence.oxm.annotations.XmlLocation;
 
import org.xml.sax.Locator;
 
@XmlRootElement
public class Customer {
 
   public int id;
 
   public String name;
 
   @XmlLocation
   @XmlTransient
   public Locator locator;
 
    @Override
    public String toString() {
        String loc = " noLoc";
        if (locator != null) {
            loc = " L" + locator.getLineNumber() + 
                  " C" + locator.getColumnNumber() +
                  " " + locator.getSystemId();
        }
 
        return "Customer(" + name + ")" + loc;
    }
 
}

Equivalent XML Bindings:

...
    <java-types>
        <java-type name="Customer">
            <xml-root-element />
            <java-attributes>
                <xml-element java-attribute="id" />
                <xml-element java-attribute="name" />
                <xml-transient java-attribute="locator" xml-location="true" />
            </java-attributes>
        </java-type>
    </java-types>
...

When a Customer is unmarshalled, the Locator field is automatically set to contain the XML location information for that object.

File f = new File("D:/temp/instance.xml"));
Customer c = jaxbContext.createUnmarshaller().unmarshal(f);
 
System.out.println(c);
 
   // Output:
   // Customer(Bob Smith) L2 C1 file:/D:/temp/instance.xml

Example 2

Accessor methods can be annotated instead of the actual Java field:

import javax.xml.bind.annotation.*;
 
import org.eclipse.persistence.oxm.annotations.XmlLocation;
 
import org.xml.sax.Locator;
 
@XmlRootElement
public class Customer {
 
   private int id;
 
   private String name;
 
   private Locator locator;
 
   @XmlLocation
   @XmlTransient
   public Locator getLocator() {
      return this.locator;
   }
 
   public void setLocator(Locator l) {
      this.locator = l;
   }
 
   ...
 
}