fastjson常规操作

1.jar包
 <!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
 <dependency>
     <groupId>com.alibaba</groupId>
     <artifactId>fastjson</artifactId>
     <version>1.2.41</version>
 </dependency>

1.map转为string
 HashMap<String ,Object> map = new HashMap<>();
 map.put("name","张三");
 System.out.println(map);
 System.out.println(JSON.toJSONString(map));

2.String 转为 jsonJSONObject  jb=  (JSONObject) JSON.parse(str);


3.java对象转为json字符串

User user = new User(1, "fengqing", "123456"); 
String userJson = JSONObject.toJSONString(user); 
System.out.println(userJson);

4.Json字符串==>java对象

JSON jsonStr = (JSON) JSON.parse(userJson);
User u = JSONObject.parseObject(userJson, User.class);

5.java集合==>Json字符串
User user1 = new User(1, "fengqing", "123456");
User user2 = new User(1, "tom", "123456");
User user3 = new User(1, "king", "123456");

List<User> users = new ArrayList<User>();
users.add(user1);
users.add(user2);
users.add(user3);

String json = JSONArray.toJSONString(users);
System.out.println(json);

6.Json字符串==>java集合
List<User> userList = JSONObject.parseArray(json, User.class);
for (User u2 : userList) {
    System.out.println(u2.getId() + "--" + u2.getUsername() + "--" + u2.getPassword());
}

7.Map==>Json
Map<String, String> map = new HashMap<String, String>();
map.put("a", "aa");
map.put("b", "bb");
map.put("c", "cc");

String jsonString = JSONObject.toJSONString(map);
System.out.println(jsonString);

8.json==>map
Map<String, String> map2 = (Map<String, String>)JSONObject.parse(jsonString);
Set<Entry<String, String>> entrySet = map2.entrySet();
for (Entry<String, String> entry : entrySet) {
    System.out.println(entry.getKey() + "--" + entry.getValue());
}

//将map按照字典序排序 

StringBuilder sb = new StringBuilder();
List<String> keys = new ArrayList<String>(map.keySet());
Collections.sort(keys);//排序。
for(String k : keys){
    String v = params.get(k);
    if(StringUtils.isNotEmpty(v)){
        sb.append(v);
    }
}