key忽略大小写 ，使用 CaseInsensitiveComparator
MySQL jdbc ResultSet  根据字段名获取值 ，就是这么处理的

 MySQL jdbc ResultSet    



String.CASE_INSENSITIVE_ORDER
public static final Comparator<String> CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator();
                                         

import java.util.Map;
import java.util.TreeMap;

public  class CaseInsensitiveTreeMap {
	
	public static void main(String[] args) throws Exception {		
		Map<String,String> map = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
		
		map.put("a", "a");
		map.put("A", "A");
		
		System.out.println(map.size());
		System.out.println(map.get("A"));
		System.out.println(map.get("a"));
	}
}

输出结果
1
A
A