See where you call, if it is Application, you should put the JAR file in the ClassPath environment variable:
If a web application can be placed under Web-INF / LIB or under Web-INF / CLASSES.
This will look at the Work range of ClassLoader.
JVM yourself when it is started, it's Boot ClassLoader loading
Rt.jar, Sunrsasign.jar, Charsets.jar, Jce.jar, JSse.jar, Plugin.jar
Then EXT ClassLoader loads JAR files under jre / lib / ext.
And ordinary Application ClassLoader loads all classes under ClassPath (library)
These are fixed load in the JVM.
For each Web Application, it has an instance of a special Web Application ClassLoader, a Web Application corresponding to a Web Application ClassLoader, which only loads the WEB-INF / LIB under this web app or a class of Web-INF / CLASSES. Classes in different web applications are not visiting.
