Java：HttpURLConnection 获取不到 JSESSIONID

String cookieValue = urlConn.getHeaderField("Set-Cookie");
Map header = urlConn.getHeaderFields();
System.out.println("header "+header);
System.out.println("JSESSIONID "+urlConn.getHeaderField("Set-Cookie"));

header 里有JSESSIONID，但是第二个打印里没哟JSESSIONID 调试结果和源码注解指出，getHeaderField ： If called on a connection that sets the same header multiple times * with possibly different values, only the last value is returned. getHeaderFields 的返回值类型 Map<String,List> ，下面贴出这个map

说明 如果Map<String,List> 的 list的size大于1，那么getHeaderField拿到 list.get(0) 所以获取方法为：

Map header = urlConn.getHeaderFields();
JSESSIONID = ((List<String>)header.get("Set-Cookie")).get(1);