Hi Tatu
I made a few changes to my POJO to avoid the circular reference issue. Now
I can write the objects to file and the output in the file is in the
format:
{ pojo }
{ pojo }
I am unable to deserialize using your technique and from the error message,
I think it is because the individual fields inside the POJO are lists
(ArrayList) and some items in the ArrayList also contain a Map (e.g.
travelDistanceMap item is a LinkedHashMap in the file attached).
The error I am seeing right now, is that when deserializing "homeList", it
says it cannot find the property "homeId" when it is clearly found in the
output and defined in the POJO. I am guessing it is because it is a list
and that is not how I am reading it back.
By the way, I am using your suggested technique of MappinIterator and
objectMapper.readValues() to read these. I am attaching 2 screenshots:
(1) IS the JSON output
(2) My deserializer code
After you take a peek at it, here are the questions:
(1) When I get the next token, should I actually check if the token ==
"homeList" and then call objectMapper.readValue(token, TypeReference)?
(2) Should I be using annotations in the class on the fields that are a
list? What about the case of travelDistanceMap where it is a Map field
inside a token?
(3) Writing this to a file with *.json and opening in an editor complains
about malformed JSON. I understand this is because I am writing out
individual JSON objects instead of a proper JSON list. Should I just rename
the file to *.txt?
Thanks in advance for your time,
MV
On Monday, December 31, 2018 at 4:22:13 PM UTC-5, MV wrote:
>
> Hi Tatu
>
> Thanks for your quick response. So I decided to try option #1 as you
> suggested i.e. continue writing single messages to a file in "append" mode
> (without using JsonGenerator) for now.
>
> I am still having trouble because it seems like my stream closes with some
> sort of NPE and circular reference. This only seems to occur when I use:
> objectMapper.writeValue(BufferedWriter (FileWriter), pojo)
>
> It is the same error when I use writeValueAsString().
>
> Instead, If I used these sequence of steps, it works.
>
> FileWrite fw = new FileWriter("myMessages.json", true);
> BufferedWriter bw = new BufferedWriter(fw);
>
> String jsonStr = objectMapper.writeValueAsString(pojo)
> bw.write(jsonStr).
>
> Of course opening "myMessages.json" file has a lot of red squiggles
> because the format is incorrect. It is just a list of messages.
> I do have these settings for ObjectMapper:
>
> *objectMapper.setSerializationInclusion(JsonInclude.Include.Non_Null)*
> *objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm a z"));*
>
> It does not look like these settings are taking effect.
>
> I am not able to find the NPE because when I look in the debugger through
> IDE (IntelliJ), nothing is null.
> The error is along the lines of NPE from circular reference. But the rest
> of the code uses the same class for future calculations and there is no NPE
> anywhere in the code.
>
> I would like to use objectMapper.writeValue(bufferedWriter, pojo) if
> possible but don't know how to resolve this circular NPE.
> I am going to try loading the values as you mentioned with "readValues()"
> and will keep you posted here.
>
> Thanks a lot for your timely responses. I really appreciate it.
>
> ~MV
>
>
> On Saturday, December 29, 2018 at 6:01:03 PM UTC-5, MV wrote:
>>
>> Hi there,
>>
>> I am using Akka Actor framework to receive messages as Java objects. When
>> I receive the message, I do the following:
>> (1) Use ObjectMapper.withPrettyWriter().writeValueAsString(<java pojo>)
>> (2) Open a file and use java.nio.Files API to write to the file. When I
>> write to the file, I use Arrays.asList(json_string_from step_1) with file
>> in *append* mode.
>>
>> I am having a few issues:
>> (1) I am unable to write the first json string as an array. When I write
>> it the first time, I *would like to see*:
>> [
>> {
>> "name" : "test"
>> "age" : 29
>> }, --> I don't get this "comma" with closing "]"
>> ] ---> don't get this.
>>
>> All I get is :
>> {
>> "name" : "test"
>> "age" : 29
>> }
>>
>> (2) While calling successive Files.write (...), the output in the file is
>> {
>> "name" : "test"
>> "age" : 29
>> }
>> {
>> "name" : "test2"
>> "age" : 30
>> }
>> This results in malformed JSON file and I cannot use
>> objectMapper.readValue as a list. Looks like I have to use Files API to
>> load the data.
>>
>> Qn) How do I write a single json as an array with ", ]" and then append
>> to this list as data starts flowing in through the messaging architecture?
>> I did see some solution on reading the file first, add new data to the
>> array and then write the whole list again to the file each time. I think
>> with messaging architecture this is not very efficient as we will see a lot
>> of messages.
>> Is there someway to open the file and write the first data and then keep
>> appending to the file?
>>
>> Thanks
>> MV
>>
>>
>>
--
You received this message because you are subscribed to the Google Groups
"jackson-user" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
For more options, visit https://groups.google.com/d/optout.
