Property “Value” is already defined. Use to resolve this conflict.

I am working on an internal project in my spare time at IBM that requires some marshalling of XML using Java. The obvious candidate is JAXB which in the main works very well. However when it fails, information on the web can be frustrating, telling you to fix it using <jaxb:property> but not actually giving you any useful information. I admit this is for a specific error that I needed to fix, but I do not think it is uncommon.

Therefore I have written a short xsd example that when run through xjc.sh (or xjc.bat on windows) exhibits the same error I was getting. The contents of the Dummy.xml file are as follows (sorry for formatting, wordpress not me!):

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:complexType name="complexTypeOne">
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="value" type="simpleTypeOne"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>

<xsd:complexType name="complexTypeTwo">
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="value" type="simpleTypeTwo"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>

<xsd:simpleType name="simpleTypeTwo">
<xsd:restriction base="xsd:string">
<xsd:pattern value="[0123456789]+"/>
</xsd:restriction>
</xsd:simpleType>

<xsd:simpleType name="simpleTypeOne">
<xsd:restriction base="xsd:token">
<xsd:enumeration value="exist"/>
<xsd:enumeration value="noexist"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:schema>

The Dummy.xml file consists of two complexTypes with an attribute of the same name, not a huge problem as the Java XML parsers run quite happily when validating XML, but when it comes to using JAXB code generation it falls over. In this case the same name is value and when run with xjc.sh produces the following error:

Property "Value" is already defined. Use <jaxb:property> to resolve this conflict.

The way to fix this issue is indeed to use a <jaxb:property> tag, and the way I found to fix this was using an external bindings file. This file will detail alternate names to use for the clashing names and will allow JAXB to parse without throwing errors. The bindings.xsd can be found here:

<jxb:bindings version="2.0"
xmlns:jxb="http://java.sun.com/xml/ns/jaxb"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<jxb:bindings schemaLocation="Dummy.xml" node="/xsd:schema">
<jxb:bindings node="//xsd:complexType[@name='complexTypeOne']">
<jxb:bindings node=".//xsd:attribute[@name='value']">
<jxb:property name="ValueToFixError1"/>
</jxb:bindings>
</jxb:bindings>
<jxb:bindings node="//xsd:complexType[@name='complexTypeTwo']">
<jxb:bindings node=".//xsd:attribute[@name='value']">
<jxb:property name="ValueToFixError2"/>
</jxb:bindings>
</jxb:bindings>
</jxb:bindings>
</jxb:bindings>

The bindings.xsd defines the xml file to perform the modifications to (schemaLocation="Dummy.xml") and then specifies using XPATH notation the relevant values to change. Fairly self explanatory if you can see the files for yourself, less so if you are just told to use tags! To specify the bindings.xsd on the command line simply do: xjc.sh -b bindings.xsd Dummy.xml which should now compile your code!

Breakdown of currentcost xml output

With all the blogject/tweetject activity going on with James Taylor, Chris Hodgins, Nick O’Leary and of course Andy-SC, and with Nick’s excellent guide to getting the data and creating custom graphs, I thought it would be good to blog about the actual xml data, and in doing so create a reference article for new people joining the currentcost foray! I do not know what all the data stands for, and this article will get updated as and when I am told/I work it out!

Updated: XML notations have been updated in line with comments to blog post. Thank you to everyone for helping with this!

<msg>
  <date>
    <dsb>00030</dsb> // This is the 'days since birth'
    <hr>00</hr><min>20</min><sec>11</sec> // The Time
  </date>
  <src>
    <name>CC02</name> // The name of the device
    <id>00077</id>  // Communication channel for device
    <type>1</type> // Hardware version of the device.
    <sver>1.06</sver> // Software version
  </src>
  <ch1>
    <watts>00168</watts> // Value from the 1st channel clamp
  </ch1>
  <ch2>
    <watts>00000</watts> // Value from the 2nd channel clamp
  </ch2>
  <ch3>
    <watts>00000</watts> // Value from the 3rd channel clamp
  </ch3>
  <tmpr>25.6</tmpr> // Current Temperature as recorded by unit
  <hist>
    <hrs> // Total Kwh used in 2 hour blocks
      <h02>000.3</h02>
      ....
      <h26>003.1</h26>
    </hrs>
    <days> // Total Kwh used per day(s)

      <d01>0014</d01>
      ....
      <d31>0000</d31>
    </days>
    <mths> // Total Kwh used per month(s)

      <m01>0000</m01>
      ....
      <m12>0000</m12>
    </mths>
    <yrs> // Total Kwh used per year(s)

      <y1>0000000</y1>
      ....
      <y4>0000000</y4>
    </yrs>
  </hist>
</msg>

Questions that I would like answered.

• Is the data stored in persistent memory? Answered by AndySC. Yes it is flash memory
• What does DSB stand for? Answered by Nick in comments below and xml above