When you come to Java XXXX, you will load the package in Java XXXX, which is java.class.path = "", while loading JDK through sun.boot.class.path = "" The JAR package under JRE / LIB / below, while also expanding all JAR packages under jdk under jdk through java.ext.dirs = jre / lib / ext - Java's web application, the web container or the server has a global classpath, for Tomcat is Common / lib, and each app has its own classpth, which is web-inf / class and web-inf / lib.
