running with invalid JAXP api or implementation axis2 using ant

I'm trying to generate axis2-1.7.9 stub files from wsdl file by calling axis2 classname="org.apache.axis2.tool.ant.AntCodegenTask"

but I keep getting the following error:

    java.lang.RuntimeException: java.lang.IllegalStateException: 
    You are running with invalid JAXP api or implementation.
    JAXP api/implementation of version 1.3.1 (included in JDK6) or higher is required.
    In case you are using ant, make sure ant 1.7.0 or higher is used - older versions of ant contain JAXP api/impl version 1.2 (in xml-apis.jar). 
    If you want to keep using older ant versions, you have to configure it to use higher the JAXP api/impl versions.

at the classpath, I'm using xalan-2.7.2.jar, xml-apis-1.4.01.jar and xercesImpl-2.12.1.jar

my ant version is:
Apache Ant(TM) version 1.9.1 compiled on May 15 2013

and my java version is: java version "1.8.0_91"
Java(TM) SE Runtime Environment (build 1.8.0_91-b15)

I don't understand what is the problem?
what I'm missing here?
from where JAXP with version 1.3.1 comes from?

I also updated the ant jars with xml-apis-1.4.01.jar and xercesImpl-2.12.1.jar

and still no luck.... what am I doing wrong?

after I updated the java the problem solved. apparently, java itself used it.