ObjectMapper 对象和json相互转换

            package
             com.mmall.util;

            import
             com.google.common.collect.Lists;

            import
             com.mmall.pojo.User;

            import
             lombok.extern.slf4j.Slf4j;

            import
             org.apache.commons.lang3.StringUtils;

            import
             org.codehaus.jackson.map.DeserializationConfig;

            import
             org.codehaus.jackson.map.ObjectMapper;

            import
             org.codehaus.jackson.map.SerializationConfig;

            import
             org.codehaus.jackson.map.annotate.JsonSerialize;

            import
             org.codehaus.jackson.type.JavaType;

            import
             org.codehaus.jackson.type.TypeReference;

            import
             java.io.IOException;

            import
             java.text.SimpleDateFormat;

            import
             java.util.Date;

            import
             java.util.List;

            /**
            
 * json转换工具类
 
            */
            
@Slf4j

            public
            class
             JsonUtil {

    
            private
            static ObjectMapper objectMapper = new ObjectMapper();
    static {
        //将对象的所有字段全部列入        objectMapper.setSerializationInclusion(JsonSerialize.Inclusion.ALWAYS);

        //取消默认转换timestamps形式,false使用日期格式转换，true不使用日期转换，结果是时间的数值157113793535
        objectMapper.configure(SerializationConfig.Feature.WRITE_DATE_KEYS_AS_TIMESTAMPS,false); //默认值true

        //忽略空Bean转json的错误
        objectMapper.configure(SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS,false);

        //所有的日期格式统一样式： yyyy-MM-dd HH:mm:ss
        objectMapper.setDateFormat(new SimpleDateFormat(DateTimeUtil.STANDARD_FORMAT));

        //忽略 在json字符串中存在，但是在对象中不存在对应属性的情况，防止错误。
        // 例如json数据中多出字段，而对象中没有此字段。如果设置true，抛出异常，因为字段不对应；false则忽略多出的字段，默认值为null，将其他字段反序列化成功
        objectMapper.configure(DeserializationConfig.Feature.FAIL_ON_NULL_FOR_PRIMITIVES,false);

    }

    //将单个对象转换成json格式的字符串（没有格式化后的json）publicstatic <T> String obj2String(T obj){
        if (obj == null){
            returnnull;
        }
        try {
            return obj instanceof String ? (String) obj:objectMapper.writeValueAsString(obj);
        } catch (IOException e) {
            log.warn("Parse object to String error", e);
            returnnull;
        }
    }

    //将单个对象转换成json格式的字符串（格式化后的json）publicstatic <T> String obj2StringPretty(T obj){
        if (obj == null){
            returnnull;
        }
        try {
            return obj instanceof String ? (String) obj:objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj);
        } catch (IOException e) {
            log.warn("Parse object to String error", e);
            returnnull;
        }
    }
    //将json形式的字符串数据转换成单个对象publicstatic <T> T string2Obj(String str, Class<T> clazz){
        if (StringUtils.isEmpty(str) || clazz == null){
            returnnull;
        }
        try {
            return clazz.equals(String.class) ? (T) str : objectMapper.readValue(str,clazz);
        } catch (IOException e) {
            log.warn("Parse object to Object error", e);
            returnnull;
        }
    }

    //将json形式的字符串数据转换成多个对象publicstatic <T> T string2Obj(String str, TypeReference<T> typeReference){
        if (StringUtils.isEmpty(str) || typeReference == null){
            returnnull;
        }
        try {
            return typeReference.getType().equals(String.class) ? (T) str : (T) objectMapper.readValue(str, typeReference);
        } catch (IOException e) {
            log.warn("Parse object to Object error", e);
            returnnull;
        }
    }

    //将json形式的字符串数据转换成多个对象publicstatic <T> T string2Obj(String str, Class<T> collectionClass, Class<?>... elementClasses){
        JavaType javaType = objectMapper.getTypeFactory().constructParametricType(collectionClass,elementClasses);
        try {
            return objectMapper.readValue(str, javaType);
        } catch (IOException e) {
            log.warn("Parse object to Object error", e);
            returnnull;
        }
    }

    //测试publicstaticvoid main(String[] args) {
//        User user1 = new User();
//        user1.setId(1);
//        user1.setUsername("wangjun1");
//        user1.setCreateTime(new Date());
//        String user1JsonPretty = JsonUtil.obj2StringPretty(user1);
//        log.info("user1JsonPretty:{}", user1JsonPretty);
//        User user2 = new User();
//        user2.setId(2);
//        user2.setUsername("wangjun2");
////        String user1Json = JsonUtil.obj2String(user1);
////        String user1JsonPretty = JsonUtil.obj2StringPretty(user1);
////        log.info("user1Json:{}", user1Json);
////        log.info("user1JsonPretty:{}", user1JsonPretty);
//////        User user = JsonUtil.string2Obj(user1Json, User.class);
//        System.out.println(user.getUsername());
////        List<User> userList = Lists.newArrayList();
//        userList.add(user1);
//        userList.add(user2);
////        String userListStr = JsonUtil.obj2StringPretty(userList);
////        log.info("==================");
//        log.info(userListStr);
////        List<User> userListObj1 = JsonUtil.string2Obj(userListStr, new TypeReference<List<User>>() {
//        });
//        System.out.println(userListObj1);
////        List<User> userListObj2 = JsonUtil.string2Obj(userListStr,List.class,User.class);
//        System.out.println(userListObj2);
//        System.out.println("end");    }
}