最近开发微信和支付宝的服务端支付，涉及到字典的排序和 url 参数转换成字典的操作，整理了一个工具类：

import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.HashMap;

import java.util.Iterator;

import java.util.LinkedHashMap;

import java.util.List;

import java.util.Map;

import java.util.Map.Entry;

import java.util.TreeMap;

public class MapUtil {

/**

* Map 按 key 进行排序

*

* @param map

* @return

*/

public static Map < String,

String > sortMapByKey(Map < String, String > map) {

if (map == null || map.isEmpty()) {

return null;

}

Map < String,

String > sortMap = new TreeMap < String,

String > (new MapKeyComparator());

sortMap.putAll(map);

return sortMap;

}

/**

* Map 按 value 进行排序

*

* @param map

* @return

*/

public static Map < String,

String > sortMapByValue(Map < String, String > oriMap) {

if (oriMap == null || oriMap.isEmpty()) {

return null;

}

Map < String,

String > sortedMap = new LinkedHashMap < String,

String > ();

List < Map.Entry < String,

String >> entryList = new ArrayList < Map.Entry < String,

String >> (oriMap.entrySet());

Collections.sort(entryList, new MapValueComparator());

Iterator < Map.Entry < String,

String >> iter = entryList.iterator();

Map.Entry < String,

String > tmpEntry = null;

while (iter.hasNext()) {

tmpEntry = iter.next();

sortedMap.put(tmpEntry.getKey(), tmpEntry.getValue());

}

return sortedMap;

}

/**

* 将 Url Params String 转为 Map

*

* @param param

* aa=11&bb=22&cc=33

* @return map

*/

public static Map < String,

Object > urlParams2Map(String param) {

Map < String,

Object > map = new HashMap < String,

Object > ();

if ("".equals(param) || null == param) {

return map;

}

String[] params = param.split("&");

for (int i = 0; i < params.length; i++) {

String[] p = params[i].split("=");

if (p.length == 2) {

map.put(p[0], p[1]);

}

}

return map;

}

/**

* 将 map 转为 Url Params String

*

* @param map

* @return aa=11&bb=22&cc=33

*/

public static String map2UrlParams(Map < String, String > map, boolean isSort) {

if (map == null) {

return "";

}

StringBuffer sb = new StringBuffer();

List < String > keys = new ArrayList < String > (map.keySet());

if (isSort) {

Collections.sort(keys);

}

for (int i = 0; i < keys.size(); i++) {

String key = keys.get(i);

String value = map.get(key).toString();

sb.append(key + "=" + value);

sb.append("&");

}

String s = sb.toString();

if (s.endsWith("&")) {

s = s.substring(0, s.lastIndexOf("&"));

}

return s;

}

}

class MapKeyComparator implements Comparator < String > {

@Override

public int compare(String str1, String str2) {

return str1.compareTo(str2);

}

}

class MapValueComparator implements Comparator < Map.Entry < String, String >> {

@Override

public int compare(Entry < String, String > me1, Entry < String, String > me2) {

return me1.getValue().compareTo(me2.getValue());

}

}

另外按 map 的 key ascii 码升序排列，还有一个更简单的办法，如下面的语句：

SortedMap smap = new TreeMap(map);

注意 map 是现成无序的字典，依赖 SortedMap和 TreeMap 转换就可以搞定了，很简单。