import com.fasterxml.jackson.databind.ObjectMapper;
public class JsonUtil { 

private static final ObjectMapper MAPPER = new ObjectMapper();
/** * 把对象转字符串 * @param data * @return */
public static String objectToJson(Object data){ 

try { 

return MAPPER.writeValueAsString(data);
}catch (Exception e){ 

e.printStackTrace();
}
return null;
}
/** * json字符串转对象 * @param jsonData * @param beanType * @param <T> * @return */
public static <T> T jsonToPojo(String jsonData, Class<T> beanType){ 

try { 

T t = MAPPER.readValue(jsonData,beanType);
return t;
}catch (Exception e){ 

e.printStackTrace();
}
return null;
}
}

ObjectMapper objectMapper = new ObjectMapper();
People peo = new People();
String jsonStr = objectMapper.writeValueAsString(peo);

ObjectMapper objectMapper = new ObjectMapper();
People peo = objectMapper.readValue(jsonStr, People.class);

ObjectMapper objectMapper = new ObjectMapper();
JavaType javaType = objectMapper.getTypeFactory().constructParametricType(List.class, People.class);
List<People> list = objectMapper.readValue(jsonStr, javaType);

Gson gson = new Gson();
String userJson = gson.toJson(userObject);

Type type = new TypeToken<List<User>>() { 
}.getType();
List<User> userLists = new Gson().fromJson(json, type);

String json = new Gson().toJson(list);