I was wondering if someone could suggest the recommended way to covert flat JSON into a complex java object.
Example JSON
{account_id: 1, user_id:3, user_name:john ... }
But my java class needs to be
class Account {
int account_id;
User user;
}
And here is the user object...
class User {
int user_id;
String user_name;
}
It looks like I could go from JSON to java using the Jackson constructor to create the object the way I need but I also need to covert the java object into a flat JSON.
Do I need to use a serializer/deserializer for each class or is there a way I can do it with simple annotations... By maybe telling it to ignore the user object but not what's inside it..
Let me know what your ideas are. Thanks
Related
I want to create an arraylist of type Adapter from a JSON. But since the JSON is not in arraylist format, I'm unable to use gson.fromJson() method.
Is there any way by which I can create a list of my custom object by parsing the following JSON?
JSON data:
"source":{"adapter-config.adapter[0].name":"testAdapter1",
"adapter-config.adapter[0].resolverName":"serviceResolver",
"adapter-config.adapter[0].parameters[0].key":"serviceId",
"adapter-config.adapter[0].parameters[0].value":"serviceIdPathInEvent",
"adapter-config.adapter[0].parameters[1].key":"appId",
"adapter-config.adapter[0].parameters[1].value":"appIdPathEvent",
"adapter-config.adapter[0].parameters[2].key":"env",
"adapter-config.adapter[0].parameters[2].value":"envPathInEvnet"}
My Adapter Object:
public class Adapter {
private String name;
private String resolverName;
private List<KeyValuePair<String, String>> attributeList;
}
Gson does not provide such functionality out of the box. However you can achieve this by manually reading the JSON data from a JsonReader, consuming the JSON property names with nextName() and then parsing them to determine which data they represent. You could either directly read from a JsonReader, or in case the shown JSON data is only an extract from a larger JSON document, you can implement a TypeAdapter for your List<Adapter>. That TypeAdapter could then either be registered with a GsonBuilder by providing new TypeToken<List<Adapter>>() {}.getType() as type, or you could annotate the field holding the List<Adapter> with #JsonAdapter.
For the actual parsing of List<Adapter>, I would recommend storing a current adapter (and its index in the list) in a local variable. Whenever you parse a JSON property name, you could then check if the index encoded in the name is equal to the index of the current adapter, then you are going to modify the existing instance, otherwise if the encoded index is equal to the index of the current adapter + 1 you create a new Adapter instance, add it to the list of adapters and reassign the current adapter variable and its index variable. Then you continue with parsing the remainder of the property name to find out which Adapter field values to set.
(In case you get stuck there, feel free to let me know in the comments and I can try to provide some concrete code; but it would probably be best if you tried it yourself first.)
I am developing a ASP.NET Core 3.1 website and I have data in a Dictionary<string, object> that I want to Serialize/Deserialize using Microsoft System.Text.Json (I am new to Json serialize/deserialize in fact). The data comes from a PostgreSQL DB query and one of the returned values is a comma-separated list of integers (converted to string) that results from the STRING_AGG function. The image below shows one of the entries of the Dictionary:
I serialize it using the following code. Please note that I have tried both Microsoft System.Text.Json and Newtonsoft.
jsonResult = Newtonsoft.Json.JsonConvert.SerializeObject(result);
//jsonResult = JsonSerializer.Serialize(result);
The data in the Dictionary should be deserialized according to the following class structure:
I use the following code:
//IEnumerable<SeccGralContenidoViewModel> seccGralContenido = JsonSerializer.Deserialize<IEnumerable<SeccGralContenidoViewModel>>(_seccGralContenidoRepository.Read());
IEnumerable<SeccGralContenidoViewModel> seccGralContenido = Newtonsoft.Json.JsonConvert.DeserializeObject <IEnumerable<SeccGralContenidoViewModel>>(_seccGralContenidoRepository.Read());
However, an exception is thrown when deserializing no matter if I use Newtonsoft or System.Text.Json:
I am originally using System.Text.Json namespace but I also tried using Newtonsoft. After analyzing a bit deeper, I see that the problem could be the way in which data is saved to the Dictionary but I have not found a workaround.
If you don't want to write a custom converter then the simplest solution is to introduce another property:
public string CategoriasContenidolds {get; set;}
private static char delimiter = ',';
[JsonIgnore]
public string[] CategoriasContenidolds_Collection
{
get => CategoriasContenidolds.Split(delimiter).Select(item => item.Trim()).ToArray();
set => CategoriasContenidolds = string.Join(delimiter, value);
}
The serializer will use the CategoriasContenidolds property during serialization and deserialization
You should use CategoriasContenidolds_Collection (or name whatever you want) in your business logic
By explicitly marking this property with JsonIgnore the serializer will ignore that
I could solve my issue by directly getting JSON formatted results from queries. PostgreSQL does an excellent job. This way I also avoid performing a 2-step process: first, getting the query result; second, serializing to JSON.
In this question How can I serialize a RealmObject to JSON in Realm for Java? The realm representative said that one can serialize realm object through GSON. Can you please explain it how?
I tried this.
RealmResults<Dog> myDogs=realm.where(Dog.class).findAll();
new Gson().toJson(myDogs);
But StackOverflowError occurred.
To make GSON serialization work with Realm you will need to write a custom JsonSerializer for each object that can be serialized and register it as a TypeAdapter.
You can see an example in this gist: https://gist.github.com/cmelchior/ddac8efd018123a1e53a
You get StackOverflow becouse of Gson based on reflection but managed object (RealmObjectProxy) have no real fields and fields of parent is nulls also some of proxy fields produses recursion in field type recognition of Gson it happens in $GsonTypes class.
To serialize RealmObject you can use one of this options:
Write your own adapter for every RealmObject childs which will takes data using getters.
Call realm.copyFromRealm(realmObject) before serialisation. It will looks like new Gson().toJson(realm.copyFromRealm(realmObject))
Use library based on 2nd option RealmSupportForGson
Hope it helps
The easier way is create a List<Dog> with RLMResult<Dog>, and then serialise this List with Gson.
After two days of bug resolve, I found this simple solution:
YourRealmObject realmObj = realm.where(YourRealmObject.class).findFirst();
if(realmObj != null) {
realmObj = realm.copyFromRealm(realmObj); //detach from Realm, copy values to fields
String json = gson.toJson(realmObj);
}
I'm trying to figure out how to adjust the way spring/jackson convert a JSON string (stored in a file) into various POJOs. For example, if I have this JSON:
{
"rates":{
"EURUSD":5.4321,
"USDHKD":1.2345
}
}
I actually want to get an instance of my 'Rates' class. Inside that I want a List containing each individual rate.
In my spring config file I created this entry:
#Bean
public ObjectMapper jsonObjectMapper() {
return new MappingJackson2HttpMessageConverter().getObjectMapper();
}
And in my service class I did this:
#Autowired
ObjectMapper jsonObjectMapper;
public Rates currentRates() {
Resource resource = this.ctx.getResource("classpath:stub/data/rates/Rates-01.json");
return this.jsonObjectMapper.readValue(resource.getURL(), Rates.class);
}
The problem is that I am trying to figure out how to take the Map containing the currencies as a single key, break those currencies in two and then create a RateEntry object containing the two currencies and the rate, before populating a list in the Rates class.
I've been looking at Spring's Conversion Service with the idea to define a converter that maps the Map to a list. i.e. this signature: Converter<Map<String, BigDecimal>, List<Rate>>. However this is based on the assumption that the JSON is first converted to standard types before the conversion service is called. An assumption I now think is incorrect.
So I'm now trying to figure out if I need to register some sort of custom ObjectMapper to handle reading directly from the JSON String data. But that sounds like over kill as I only want to adjust part of the object graph, and let the default converters handle the rest.
Any pointers appreciated. Thanks.
Ok, Jackson tries to stay away from structural transformations (since it's a quick-sand pit with unlimited number of general permutations). But it might be possible to use some existing features to do what you want.
First: to use Object key to indicate type, you will probably want to enable polymorphic type handling with "as object wrapper" inclusion.
So add something like:
#JsonTypeInfo(as=Include.WRAPPER_OBJECT)
for your Rates class declaration.
As to converting values into list; this might work by defining "any-setter" (see http://www.cowtowncoder.com/blog/archives/2011/07/entry_458.html), something like:
#JsonAnySetter
public void set(String key, Double value) // or "Object value")
{
list.add(new Rate(key, value));
}
I hope this helps.
I'm trying to change the (de)serialization of a list in one of my classes.
the objects in the list shall be serialised as int (their jpa id) and deserialised accordingly. serialization is simple.
for the deserialization i have a class that can translate the id into the object if id and class are known.
How do i get the necessary class from jackson? all default jackson serialisers have a constructor like this: protected StdDeserialiser(Class<?> vc) so the information is present somewhere.
is there a way to access it during deserialisation?
or before the deserialiser is constructed by jackson?
or inside the HandlerInstantiator?
I only want to overwrite the default deseriliser for certain references so i can't just write a provider or a custom module.
I made it work from inside the deserializer with the help of the ContextDeserializer interface as this supplies the deserializer with the target property.
public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) throws JsonMappingException {
Class<?> vc = null;
if (property.getType().isCollectionLikeType()) {
vc = property.getType().getContentType().getRawClass();
} else {
vc = property.getType().getRawClass();
}
return new ResourcePathDeserializer(vc, converter);
}
This solution is not perfect as I only get the raw class of the return type or the generic (which might be a parent class or an interface) but that is enough for my requirements.
It would be better if I could access the "real" class that was resolved by Jackson, but for me this works.
First of all, there is nothing fancy about writing a Module: it is just a way for plugging things in, like custom (de)serializers. So no need to avoid that. And you will most like need to write a module to do what you want.
In general it is not a good idea to try to create "universal" serializers or deserializers, and it will probably run into problem. But it depends on what exactly you are trying to do.
Type information will either be:
Implicit from context: you are writing a (de)serializer for type T, and register it for it, so that's your type
Passed by Jackson when (de)serializer is being constructed, via Module interface: modules are asked if they happen to have a (de)serializer for type T. SimpleModule will only use basic Class-to-impl mapping (that's where "simple" comes from); but full custom Module has access to incoming type.
But I don't know if above will work for your use case. Type information must be available from static type (declared content type for the list).