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EclipseLink/Release/2.4.0/JAXB RI Extensions/XML Location

Design Documentation: @XmlLocation

ER 355766

In the current JAXB RI, developed by Sun, there are a series of "proprietary" JAXB extensions that are available to provide advanced JAXB functionality outside of the JAXB spec (these extension classes 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).

This document will outline the design for an EclipseLink equivalent to this extension.


  • Deliver an @XmlLocation annotation in the EclipseLink library that will provide the same functionality as the Sun extension.
    • Line number
    • Column number
    • System ID, if applicable
  • Support drop-in-replacement functionality if the user is currently using the Sun versions of this annotation (com.sun.xml.bind.annotation.XmlLocation or com.sun.xml.internal.bind.annotation.XmlLocation)
  • Have zero impact on memory/performance if the user is not using @XmlLocation.


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 Ok green.gif Ok green.gif Ok green.gif Ok green.gif Ok green.gif Delete.gif Ok green.gif Ok green.gif Delete.gif Ok green.gif Ok green.gif Ok green.gif Ok green.gif Ok green.gif Delete.gif Ok green.gif Ok green.gif Delete.gif
org.w3c.dom.Node Delete.gif Delete.gif Delete.gif
org.xml.sax.InputSource Ok green.gif Ok green.gif Delete.gif


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 (om.sun.xml.bind.annotation.XmlLocation and com.sun.xml.internal.bind.annotation.XmlLocation).


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}) 
public @interface XmlLocation {}

XML Bindings


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

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.


The following examples refer to this XML instance document:

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

Example 1

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


import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlLocation;
import org.xml.sax.Locator;
public class Customer {
   public int id;
   public String name;
   public Locator locator;
    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-type name="Customer">
            <xml-root-element />
                <xml-element java-attribute="id" />
                <xml-element java-attribute="name" />
                <xml-transient java-attribute="locator" xml-location="true" />

When a Customer is unmarshalled, the Locator field is automatically set to contain the XML location information for that object. By default, if that object was then marshalled back to XML, the XML location information would be written out as well.

Unmarshalling and Marshalling:

File f = new File("D:/temp/instance.xml"));
Customer c = jaxbContext.createUnmarshaller().unmarshal(f);
   // Output:
   // Customer(Bob Smith) L15 C35 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;
public class Customer {
   private int id;
   private String name;
   private Locator locator;
   public Locator getLocator() {
      return this.locator;
   public void setLocator(Locator l) {
      this.locator = l;


When processing XML through our various parsing mechanisms (UnmarshalRecord, SAXDocumentBuilder, XMLStreamReaderReader, etc), a Locator object is supplied by the underlying parser libraries. This Locator is constantly updated throughout the unmarshalling process (with the location of the currently parsed node). When parsing a startElement(), if that element equates to a Descriptor that is location-aware, the Locator will be cloned at that point, and stored on the UnmarshalRecord, indicating the XML Location of that object in XML.

  • New annotation: org.eclipse.persistence.oxm.annotations.XmlLocation
  • New boolean "xml-location" flag on "xml-transient" and "xml-element" in XML Bindings
    • Must be added to new 2.4 schema - eclipselink_oxm_2_4.xsd
    • Corresponding updates to o.e.p.jaxb.xmlmodel classes

  • New field on XMLDescriptor: boolean isLocationAware

  • New field on UnmarshalRecord: Locator xmlLocation (each object instance has its own UnmarshalRecord, and this will be set only if Descriptor isLocationAware)

  • New field on Property: boolean isXmlLocation
    • Property is set up for isXmlLocation in AnnotationsProcessor and XMLProcessor

  • MappingsGenerator: in generateMapping(), create a specialized XMLCompositeObjectMapping for the Locator property
  • New class: NullInstantiationPolicy - we want to create a regular mapping for the Locator, but will never be instantiating it like a regular mapping - its value will be set manually during parsing. Plus, Locator does not have a default constructor. This InstantiationPolicy simply returns null for buildNewInstance().

  • New constants in XMLConstants: LOCATOR_CLASS and LOCATOR_CLASS_NAME

  • New JAXBException ("XmlLocation is only allowed on properties of type org.xml.sax.Locator, but [{0}] is of type [{1}].")

Document History

Date Author Version Description & Notes
110926 Rick Barkhouse 1.00 : First draft
110927 Rick Barkhouse 1.01 : Added design information
111012 Rick Barkhouse 1.02 : Added Schema Generation requirement to Behaviour

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