When you start weblogic service reported the following error
org.xml.sax.SAXException: SAX2 driver class org.apache.xerces.parser.SAXParser does not implement XMLReader
java.lang.ClassCastException: org.apache.xerces.parsers.SAXParser cannot be cast to org.xml.sax.XMLReader...，
Serverlet cause behind the service failed to load <Servlet: "InitServlet" failed to preload on startup in Web application: "/ abc".
java.lang.ExceptionInInitializerError at ....>
Find the Internet a lot, there are said to jdk version of the problem, there are also problems jar package, replacing what jar package, less cited jar package, etc., no longer is a problem in xml format.
I appeared here, because the deployment file inside the META-INF / MANIFAST.MF document which specifies a Class-Path, but the path to the actual deployment environment should not be the same, resulting in an error, and delete all the inside of the Class-Path, restart weblogic it.