从数据库中取出的值，循环放入map中，再把map放中list中，问怎样取出map中的key值

回答3：

//方法一、
HashMap map = new HashMap();
Set valueSet = map.entrySet();//hashMap中的value遍历
Iterator iterator = valueSet.iterator();
List list = new ArrayList();//值list
while(iterator.hasNext()){
Object object = iterator.next();
list.add(object);
}
//方法二、
HashMap map = new HashMap();
Set keySet = map.keySet();//hashMap中的key遍历
Iterator keyIterator = keySet.iterator();
List keyList = new ArrayList();//key list
List valueList = new ArrayList();//值 list
while(keyIterator.hasNext()){
Object object = keyIterator.next();
keyList.add(object);
valueList.add(map.get(object));
}