Jackson how to transform JsonNode to ArrayNode without casting

Question

I am changing my JSON library from org json to Jackson and I want to migrate the following code   JSONObject datasets   readJSON new URL DATASETS    JSONArray datasetArray    datasets getJSONArray  datasets      Now in Jackson I have the following   ObjectMapper m   new ObjectMapper    JsonNode datasets   m readTree new URL DATASETS          ArrayNode datasetArray    ArrayNode datasets get  datasets      However I don t like the cast there  is there the possibility for a ClassCastException  Is there a method equivalent to getJSONArray in org json so that I have proper error handling in case it isn t an array

User · Answer

In Java 8 you can do it like this   import java util    import java util stream     List lt JsonNode gt  datasets   StreamSupport      stream datasets get  datasets   spliterator    false       collect Collectors toList

User · Answer

I would assume at the end of the day you want to consume the data in the ArrayNode by iterating it  For that    Iterator lt JsonNode gt  iterator   datasets withArray  datasets   elements    while  iterator hasNext             System out print iterator next   toString              or if you re into streams and lambda functions   import com google common collect Streams  Streams stream datasets withArray  datasets   elements         forEach  item - gt  System out print item toString

User · Answer

Yes  the Jackson manual parser design is quite different from other libraries  In particular  you will notice that JsonNode has most of the functions that you would typically associate with array nodes from other API s  As such  you do not need to cast to an ArrayNode to use  Here s an example   JSON          objects      One    Two    Three       Code   final String json       objects        One      Two      Three        final JsonNode arrNode   new ObjectMapper   readTree json  get  objects    if  arrNode isArray          for  final JsonNode objNode   arrNode            System out println objNode             Output       One     Two     Three    Note the use of isArray to verify that the node is actually an array before iterating  The check is not necessary if you are absolutely confident in your datas structure  but its available should you need it  and this is no different from most other JSON libraries

User · Answer

Is there a method equivalent to getJSONArray in org json so that I have proper error handling in case it isn t an array    It depends on your input  i e  the stuff you fetch from the URL   If the value of the  datasets  attribute is an associative array rather than a plain array  you will get a ClassCastException   But then again  the correctness of your old version also depends on the input   In the situation where your new version throws a ClassCastException  the old version will throw JSONException   Reference  http   www json org javadoc org json JSONObject html getJSONArray java lang String

[java] Jackson how to transform JsonNode to ArrayNode without casting?

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