List of JsonString to list of User Objects conversion

Question

Not the duplicate of How to use Jackson to deserialise an array of objects.

Here in the list ,items are string within double quotes.

I am trying to convert a list of messages which are jsonString to List of UserDefined objects. I have input like this.

[
    "{\"id\":\"5\",\"type\":\"abc\",\"innerObject\":{\"id\":\"8\"}}"
]

What is the method to convert this list to List of MyClass.

class MyClass{
String id;
String type;
Inner inner;
//getters and setters
}
class Inner{
String id;
//getters and setters
}

I have tried

objectMapper.readValue(jsonFormattedString, new TypeReference<List<MyClass>>(){});

Also this

Type listType = new TypeToken<ArrayList<MyClass>>() {}.getType();
myList = new Gson().fromJson(jsonFormattedString, listType);

But not working.

Expected output is

[{"id":"5","type":"abc","innerObject":"8"}]

You have innerObject inside the jsonString, but the property in the MyClass is called inner and not innerObject. Can it be that the problem why it's not working? — Roxana Roman, Oct 08 '19 at 19:13
But the error is even before that as the input list contains String with double quotes. — user3763375, Oct 08 '19 at 19:18
You should be able to iterate the string array and use `GSON`'s `fromJson` method to convert to your type. https://static.javadoc.io/com.google.code.gson/gson/2.8.5/com/google/gson/Gson.html#fromJson-java.lang.String-java.lang.Class- — The Head Rush, Oct 09 '19 at 18:26

Joey · Answer 1 · 2019-10-08T19:09:20.720

0

For the readValue method of ObjectMapper, the second argument should be the class and not a class instance. For example, if this were a single item you would call readValue as shown below:

objectMapper.readValue(jsonFormattedString, TransEvent.class);

For a generic list, this can be accomplished either of the following ways:

// list
objectMapper.readValue(jsonFormattedString, new TypeReference<List<TransEvent>>(){});

// list
objectMapper.readValue(jsonFormattedString, objectMapper.getTypeFactory().constructCollectionType(List.class, TransEvent.class));

// array
TransEvent[] transEvents = objectMapper.readValue(jsonFormattedString, TransEvent[].class);

edited Oct 08 '19 at 19:09

answered Oct 08 '19 at 18:57

Joey

670
8
14

yes. If the object was single item. But it is list and with String items. – user3763375 Oct 08 '19 at 18:59
@user3763375 I forgot about type erasure for generics, I've updated my response – Joey Oct 08 '19 at 19:04
@user3763375 You can actually also use the basic array type as well, I added the example using `TransEvent[].class` just now – Joey Oct 08 '19 at 19:09
com.fasterxml.jackson.core.JsonParseException: Unexpected close marker ']': expected '}' (for root starting at [Source: ] when I tried objectMapper.readValue(jsonFormattedString, objectMapper.getTypeFactory().constructCollectionType(List.class, TransEvent.class)); – user3763375 Oct 08 '19 at 19:16
I think the problem is input list contains string with double quotes. – user3763375 Oct 08 '19 at 19:16

List of JsonString to list of User Objects conversion

1 Answers1