调用过程： java\util\HashMap#readObject(java.io.ObjectInputStream s) java\util\HashMap#hash(Object key)
获取key（这里是URL）的hashCode java\net\URL#hashCode
java\net\URLStreamHandler#hashCode(URL u)
调用栈：
<init>:102, Inet4Address (java.net) lookupAllHostAddr:-1, Inet6AddressImpl (java.net) lookupAllHostAddr:928, InetAddress$2 (java.net) getAddressesFromNameService:1323, InetAddress (java.net) getAllByName0:1276, InetAddress (java.net) getAllByName:1192, InetAddress (java.net) getAllByName:1126, InetAddress (java.net) getByName:1076, InetAddress (java.net) getHostAddress:442, URLStreamHandler (java.net) hashCode:359, URLStreamHandler (java.net) hashCode:885, URL (java.net) hash:339, HashMap (java.util) readObject:1410, HashMap (java.util) invoke0:-1, NativeMethodAccessorImpl (sun.reflect) invoke:62, NativeMethodAccessorImpl (sun.reflect) invoke:43, DelegatingMethodAccessorImpl (sun.reflect) invoke:498, Method (java.lang.reflect) invokeReadObject:1158, ObjectStreamClass (java.io) readSerialData:2176, ObjectInputStream (java.io) readOrdinaryObject:2067, ObjectInputStream (java.io) readObject0:1571, ObjectInputStream (java.io) readObject:431, ObjectInputStream (java.io) main:36, URLDNSPoC (marshalsec)