AppClassLoader
AppClassLoader应用类加载器，又称系统类加载器，负责在JVM启动时加载来自命令java中的classpath或者java.class.path系统属性或者CLASSPATH操作系统属性所指定的JAR类包和类路径
Bootstrap ClassLoder、ExtClassLoader、AppClassLoader这么多ClassLoader，它们是从哪里加载class的，这个问题jdk源码中sun.misc.Launcher已经给出回答：Bootstrap ClassLoder加载的是System.getProperty("sun.boot.class.path");、ExtClassLoader加载的是System.getProperty("java.ext.dirs")、AppClassLoader加载的是System.getProperty("java.class.path")，
https://juejin.im/post/5c7a41b0e51d4550690476b3
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