Map 集合按字母排序方法

@Test
public void testMapSort() {
    Map<String, String> map = new HashMap<>();
    map.put("bdc", "bbb");
    map.put("caf", "ccc");
    map.put("aef", "aaa");
    map.put("def", "ddd");
    System.out.println("排序前:" + map);

    //進行排序
    List<Map.Entry<String, String>> entries = new ArrayList<Map.Entry<String, String>>(map.entrySet());
    Collections.sort(entries, new Comparator<Map.Entry<String, String>>() {
        @Override
        public int compare(Map.Entry<String, String> o1, Map.Entry<String, String> o2) {
            return o1.getKey().compareTo(o2.getKey());
        }
    });
    System.out.println("排序后:" + entries);

    //將key，value拼接
    StringBuffer sb = new StringBuffer();
    entries.forEach(x -> sb.append(x.getKey()).append(x.getValue()));
    System.out.println("拼接后結果:" + sb.toString());
}
控制台輸出結果：

排序前:{bdc=bbb, aef=aaa, def=ddd, caf=ccc}

排序后:[aef=aaa, bdc=bbb, caf=ccc, def=ddd] 

拼接后結果:aefaaabdcbbbcafcccdefddd