jackson objectMapper json字符串、对象bean、map、数组list互相转换常用的方法

- 对象转json字符串

User user=new User();
String userJson=mapper.writeValueAsString(user);

- Map转json字符串

Map map=new HashMap();  
String json=mapper.writeValueAsString(map);

- 数组list转json字符串

Student[] stuArr = {student1, student2};  
String jsonfromArr =  mapper.writeValueAsString(stuArr);

- json字符串转对象

String expected = "{\"name\":\"Test\"}";
User user = mapper.readValue(expected, User.class);

- json字符串转Map

String expected = "{\"name\":\"Test\"}";
Map userMap = mapper.readValue(expected, Map.class);

- json字符串转对象数组List

String expected="[{\"a\":12},{\"b\":23},{\"name\":\"Ryan\"}]";
CollectionType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class, User.class);
List<User> userList = mapper.readValue(expected, listType);

- json字符串转Map数组List>

String expected="[{\"a\":12},{\"b\":23},{\"name\":\"Ryan\"}]";
CollectionType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class, Map.class);
List<Map<String,Object>> userMapList = mapper.readValue(expected, listType);

- jackson默认将对象转换为LinkedHashMap

String expected = "[{\"name\":\"Ryan\"},{\"name\":\"Test\"},{\"name\":\"Leslie\"}]";
ArrayList arrayList = mapper.readValue(expected, ArrayList.class);

- json字符串与list或map互转的方法

ObjectMapper objectMapper = new ObjectMapper();
 //遇到date按照这种格式转换
 SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
 objectMapper.setDateFormat(fmt);
 
  String preference = "{name:'张三'}";
        //json字符串转map
  Map<String, String> preferenceMap = new HashMap<String, String>();
  preferenceMap = objectMapper.readValue(preference, preferenceMap.getClass());
  
  //map转json字符串
  String result=objectMapper.writeValueAsString(preferenceMap);

- bean转换为map

List<Map<String,String>> returnList=new ArrayList<Map<String,String>>();
List<Menu> menuList=menuDAOImpl.findByParentId(parentId);
ObjectMapper mapper = new ObjectMapper();
returnList=mapper.convertValue(menuList,new TypeReference<List<Map<String, String>>>(){});