I am trying to convert GSON to jackson I have a method that returns a gson JsonObject. However it only creates a JsonArray, and returns that so I assume there is a simple casting there. So what would be the Jackson Equivalent? Now the method only adds one string at a time. So I need something like this:
JsonNode node = new JsonNode();
node.add("String 1");
node.add("String 2');
but would come out like this:
["String 1","String 2"]
I could create a List and map it from there, but I want to do this raw.
This seems too simple as google has given me many suggestions that are far beyond what this simple exercise requires.
And if anyone has a nice blog to tutorial on how to convert Gson to Jackson that would be great.
it is a bit tricky - you create an array node through JsonNode factory method:
ArrayNode arrNode = (ArrayNode)new JsonNode().withArray("my_array"); // arg is arrray propertry name
arrNode.add("String 1");
arrNode.add("String 2');
If you just want to create ArrayNode, ObjectMapper has method createArrayNode(), along with createObjectNode(). You can then add entries to it, as well as add node itself into other arrays, or as property in ObjectNode.
Actual construction of nodes by mapper is done using configurable JsonNodeFactory; default implementation of which simple constructs one of standard implementation types like ObjectNode and ArrayNode.
Related
I saw a tutorial where an extra class is created just to be able to serialize a list of objects, instead of a single object:
I'm using json_serializable to generate some serialization code for my class Preference, but now I want to save a list of preferences using shared_preferences and I get an error obviously.
var sSavedPrefs = json.encode(PreferenceRepo.getSavedPrefs());
prefs.setString(saved_prefs_key, sSavedPrefs );
I used
#JsonSerializable()
class Preference{...}
to make it serializable, but I don't want to create an extra class like
#JsonSerializable()
class Preferences{...}
just to make it work - is there a better way?
I found a way:
Using the setStringList method I could create a List where I added each serialized object one by one without needing an extra list class. I also noticed that json.encode might not have been the right method to use, I saw jsonEncode in another tutorial and used it instead:
List<String> savedPrefsJson = [];
for (Preference savedPref in PreferenceRepo.savedPrefs) {
String savedPrefJson = jsonEncode(savedPref);
savedPrefsJson.add(savedPrefJson);
}
prefs.setStringList(saved_prefs_key, savedPrefsJson);
I learned from one example, so I am not sure if this is the optimal way or not, but anyways, I use the following code. I create one Retrofit instance and use it for all requests.
Since there are many methods, there are many types of data. It seems that I can create adapters (json -> my data class) automatically simply by adding annotations. But I needed more control (inheritance: the data classes have shared fields, dependency: some fields may not exist depending on other field's values), so I created a custom adaptor for each of the classes. So, currently my code is like this:
if (instance == null)
{
val gson = GsonBuilder()
.registerTypeAdapter(myClass1::class.java, myClassDeserialiser1())
.... (tens of this) ....
.registerTypeAdapter(myClass30::class.java, myClassDeserialiser30())
.create()
instance = Retrofit.Builder().
.addConverterFactory(GsonConverterFactory.create(gson))
.build()
.create(MyAPIs::class.java);
}
return instance
The problem above is that I am creating instances of all parsers at the same time in advance. This may be inefficient. I wish I could create them when they are first needed. Is that possible?
You can add a #JsonAdapter annotation to your class definition in lieu of calling registerTypeAdapter. I can't comment on its efficiency, but it keeps the adapter info tied to the object instead of the creation of your Gson object, which sounds like what you want.
I use Jackson 2.5.0.
I would like to write a method which takes arbitrary JSON-string and sorts every property by key alphabetically with Jackson. Including nested ones.
I learned there is a SORT_PROPERTIES_ALPHABETICALLY feature of Jackson's ObjectMapper which I wanted to use in order to achieve my goal. So my initial code based on this idea is:
class FooBar {
String foo
String bar
}
def sortFields(String source) {
def om = new ObjectMapper().configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true)
def obj = om.readValue(source, Map.class)
return om.writeValueAsString(obj)
}
println sortFields('{"foo":"f","bar":"b"}')
Notice that I can't know ahead what structure input JSON has so Jackson unmarshalls it as a Map by default (LinkedHashMap to be more precise).
I expected it to output a string with keys sorted alphabetically:
{"bar":"b","foo":"f"}
Unfortunately with the snippet above SORT_PROPERTIES_ALPHABETICALLY does not work when object to serialize is a Map. If I replace Map.class with FooBar.class my JSON properties will be sorted as expected. But as I said, I can't know ahead a type of input JSON and have a class in my code for any type possible. What other options do I have with Jackson?
This works for the top level map:
objectMapper.configure(
SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true
);
Sadly it doesn't sort keys in any potential nested map you may have.
I'm new to Kotlin, so apologies if I'm not articulating concepts correctly. I have an instance of an Entity
[TestEntity(applicationId=1, timestamp=2018-01-24T18:40:30, issueState=MA, product=test, status=sold, paymentMode=VISA, premium=null)]
I am writing a service that is going to take these keys and use them to create the headers of a report. The keys may change depending on the type of report the user is trying to generate, which will have an impact on the Entity that will be instantiated.
I want to be able to iterate over this Entity so that I can create an array to use for the headers. Any thoughts on how I do this?
I think the cleanest solution is storing values in a map and delegating properties to it.
Don't think you can otherwise iterate over class fields without some verbose getter chain or ugly reflection shenanigans.
For example here you can access map fields as if they were class fields, but can also easily iterate over map.
data class TestEntity(val map : Map<String, Any>){
val appId : Int by map
val timeStamp : Long by map
(... more fields)
}
I would like to leverage the Jackson infrastructure to transform an untyped Map/List structure into a POJO hierarchy.
What I need is pretty close to
jsonNode = objectMapper.valueToTree(MapHierarchy) followed by
pojoTree = objectMapper.treeToValue(jsonNode)
...except that I need to modify the field names on the fly: the names found in the source Map/List hierarchy are declared as custom annotations on the POJO class.
Here is a complete example:
public class Cat
{
#MapField("attr:col")
#JsonProperty("color")
private String _color;
}
... and the source Map:
{
"attr:col" -> "black"
}
... from which I would like to obtain a Cat instance.
I am sure there has got to be an elegant way to achieve this with the Jackson APIs, but I can't quite figure out how... any suggestions? Obviously I don't want to create a second parallel class hierarchy just to describe the deserialization of the Map through annotations.
An extra bonus would be to be able to transform the Map without going through stringified JSon which I believe is how valueToTree works.