If you are using a JDK that has a bundled JAXP implementation (i.e. parser in this case e.g. jdk 1.6, 1.5) you do not need to do anything.
However ff you want to use a different implementation than the bundled one then you have to choose one of the mechanisms set out in your link before the JVM falls back to the platform default, bundled implementation.
put the third party implementation in the class path. create JAVA_HOME/jre/lib/jaxp.properties if it does not exist already. in the file add the following line... javax.xml.parsers.DocumentBuilderFactory=fully.qualified.classname.of.the.thirdparty.DocumentBuilderFactoryClass
But usually if the implementation is distributed in a jar the service mechanism in the jar is already set up. If you extract the jar and check the file META-INF/services/javax.xml.parsers.DocumentBuilderFactory you can verify this. In which case you only have to add the jar to the classpath.