json工具类序列化和反序列化方法

类文件中，初始化：

private static final ObjectMapper MAPPER = new ObjectMapper();

String response = xxx;

response  {"id":"1","name":"zhangsan","password":"123",......}

将response的json字符串转为User对象（反序列化）

User user = MAPPER.readValue(response,User.class);

将User对象转为json字符串（序列化）

String value = MAPPER.writeValueAsString(user);