文章目录
1. json字符串简介2. 转换工具3. json与obj相互转换2.1 obj转json字符串2.2 json字符串转obj2.3 转换为List类型2.4 转化为Map类型2.5 特殊格式字段转换字符串与变量名转换转换日期 4. json转换工具4.1 常用版本4.2 Optional 取代null的版本1. json字符串简介
JSON(JavaScript Object Notation)是一种轻量级数据交换格式,具有格式简单、易于读写、占用带宽少等有点,常被用于序列化和反序列化的中间格式。通俗的理解:json是一个有规则的字符串,它的表达(表现)形式是键值对,非常类似于Java语言中的Map,主要用于交互的一种数据格式
。
2. 转换工具
json转换常用的类库有Jackson、GoogleGson、Json-lib、Flexjson、Json-io、Genson、JSONiJ等7种,其中Jackson使用较为流行,本文基于Jackson介绍。
3. json与obj相互转换
Jackson默认使用BeanSerializer序列化POJO,要求对应的字段为public类型或者有对应的getter()方法。
2.1 obj转json字符串
ObjectMapper mapper = new ObjectMapper();mapper.configure(SerializationFeature.INDENT_OUTPUT, true); //输出格式化//设置输出时间格式SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss);mapper.setDateFormat(dateFormat);//Map按序输出mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);Object obj;String result = mapper.writeValueAsString(obj);
2.2 json字符串转obj
String str;ObjectMapper mapper = new ObjectMapper();Object result = mapper.readValue(str, Object.class);
2.3 转换为List类型
String str;ObjectMapper mapper = new ObjectMapper();List<Object> result = mapper.readValue(str, new TypeReference<List<Object>>() {});
2.4 转化为Map类型
String str;ObjectMapper mapper = new ObjectMapper();Map map = mapper.readValue(str, Map.class);
2.5 特殊格式字段转换
字符串与变量名转换
@JsonProperty(value = "short_name")public String shortName;
转换日期
@JsonFormat
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", locale = "zh", timezone = "GMT+8")public Date date;
Jackson在序列化时间时是按照国际标准时间GMT格式化的,而国内默认时区是CST时区,及北京时区东八区,两者相差8小时。
4. json转换工具
最后,提供给大家两个完整的json转换工具,功能强大,可以直接使用。
4.1 常用版本
public class JsonUtils {private static final ObjectMapper MAPPER = new ObjectMapper();private static final Logger logger = LoggerFactory.getLogger(JsonUtils.class);public static String toString(Object obj) {if (obj == null) {return null;}if (obj.getClass() == String.class) {return (String) obj;}try {return MAPPER.writeValueAsString(obj);} catch (JsonProcessingException e) {logger.error("json序列化出错:" + obj, e);return null;}}public static <T> T toBean(String json, Class<T> tClass) {try {return MAPPER.readValue(json, tClass);} catch (IOException e) {logger.error("json解析出错:" + json, e);return null;}}public static <E> List<E> toList(String json, Class<E> eClass) {try {return MAPPER.readValue(json, MAPPER.getTypeFactory().constructCollectionType(List.class, eClass));} catch (IOException e) {logger.error("json解析出错:" + json, e);return null;}}public static <K, V> Map<K, V> toMap(String json, Class<K> kClass, Class<V> vClass) {try {return MAPPER.readValue(json, MAPPER.getTypeFactory().constructMapType(Map.class, kClass, vClass));} catch (IOException e) {logger.error("json解析出错:" + json, e);return null;}}/*** 把json字符串反序列化,当反序列化的结果比较复杂时,通过这个方法转换*/public static <T> T nativeRead(String json, TypeReference<T> type) {try {return MAPPER.readValue(json, type);} catch (IOException e) {logger.error("json解析出错:" + json, e);return null;}}}
4.2 Optional 取代null的版本
利用Java8 Optional 取代null的json转换工具
/*** 可以避免空指针异常的json转换工具* Create by @author BG331145 杨威 on /1/20 0020 - 16:58*/public class JsonUtilOptional {public static final ObjectMapper mapper = new ObjectMapper();private static final Logger logger = LoggerFactory.getLogger(JsonUtils.class);public static Optional<String> toString(Object obj) {if (obj == null) {return Optional.empty();}if (obj.getClass() == String.class) {return Optional.of(obj.toString());}try {return Optional.ofNullable(mapper.writeValueAsString(obj));} catch (JsonProcessingException e) {logger.error("json序列化出错:" + obj, e);return Optional.empty();}}public static <T> Optional<T> toBean(String json, Class<T> tClass) {try {return Optional.ofNullable(mapper.readValue(json, tClass));} catch (IOException e) {logger.error("json解析出错:" + json, e);return Optional.empty();}}public static <E> Optional<List<E>> toList(String json, Class<E> eClass) {try {return Optional.ofNullable(mapper.readValue(json, mapper.getTypeFactory().constructCollectionType(List.class, eClass)));} catch (IOException e) {logger.error("json解析出错:" + json, e);return Optional.empty();}}public static <K, V> Optional<Map<K, V>> toMap(String json, Class<K> kClass, Class<V> vClass) {try {return Optional.ofNullable(mapper.readValue(json, mapper.getTypeFactory().constructMapType(Map.class, kClass, vClass)));} catch (IOException e) {logger.error("json解析出错:" + json, e);return Optional.empty();}}/*** 把json字符串反序列化,当反序列化的结果比较复杂时,通过这个方法转换*/public static <T> Optional<T> nativeRead(String json, TypeReference<T> type) {try {return Optional.ofNullable(mapper.readValue(json, type));} catch (IOException e) {logger.error("json解析出错:" + json, e);return Optional.empty();}}}