Perform checks against XML files, such as Oracle OSB files and Soap-UI test files
You might try to use XmlUnit for such purposes.
You would write your checks in form of JUnit tests in that scenario. Simple XPath based checks are easily performed with the help of XmlUnit assertion methods such as assertXpathExists, assertXpathsEqual etc.
More complex checks might be implemented using a custom NodeTester.
some Python code can help, for a simple working example of Checkstyle with OSB see:
http://www.javamonamour.org/2013/07/lintcheckstyle-for-osb.html
I have used Schematron in the past, it's just not flexible enough.