I have a problem with my custom JSON deserializer.
I use Jackson to map JSON to Java and back. In some cases I need to write my own mapping.
I have an object (filter), which contains a set of another object(metaInfoClass). I try to deserialize the filter with Jackson, but I implemented an own deserializer for the inner object.
The JSON looks like this:
{
"freetext":false,
"cityName":null,
"regionName":null,
"countryName":null,
"maxResults":50,
"minDate":null,
"maxDate":null,
"metaInfoClasses":
[
{
"id":31,
"name":"Energy",
"D_TYPE":"Relevance"
}
],
"sources":[],
"ids":[]
}
My deserializer just works fine, it finds all the fields etc.
The problem is, that somehow (no idea why) the deserializer gets invoked on the rest of the JSON string, so the sources token is getting processed, and so on.
This is very weird, since I don't want to deserialize the big object, but only the inner metaInfoClass.
Even more weird: the CollectionDeserializer class keeps calling my deserializer with the json string even after it is ended. So nothing really happens, but the method gets called.
Any idea?
Thanks a lot!
I was able to find a solution.
I modified the implementation (in the deserialize method) to use to following code:
JsonNode tree = parser.readValueAsTree();
Iterator<Entry<String, JsonNode>> fieldNameIt = tree.getFields();
while (fieldNameIt.hasNext()) {
Entry<String, JsonNode> entry = fieldNameIt.next();
String key = entry.getKey();
String value = entry.getValue().getTextValue();
// ... custom code here
}
So with this approach, it was parsing only the right piece of the code and it's working right now.
Related
I'm trying to create a custom deserializer for generic lists. Lets say I get a json representation of class B:
public class B{
List<A> listObject;
}
where A is some other class which I see only at runtime. I'd like to create a deserializer that will be able to infer the type of listObject as list with inner type A and deserialize it as such instead of using the default hashmap deserializer.
I tried using contextual deserializer, similar to what was suggested here
and then adding it as a custom deserializer for List
addDeserializer(List.class, new CustomListDeserializer())
But I'm not sure how am I supposed to read the json and create the list in deserialize function (in the Wrapper example above it's pretty simple, you read the value and set it as a value field, but if my 'wrapper' is List, how do I read the values and add them?)
I tried using readValue with CollectionType constructed with constructCollectionType(List.class, valueType) but then I go into an infinite loop, since readValue uses the deserializer from which it was called.
Any ideas?
Thanks for the suggestion. I solved it by parsing the json as an array of inner generic type and then converting to list, as follows:
Class<?> classOfArray = Array.newInstance(valueType.getRawClass(), 0).getClass();
Object[] parsedArray = (Object[]) parser.getCodec().readValue(parser, classOfArray);
return Arrays.asList(parsedArray);
Firstly, please forgive any rookie mistakes here - I'm not a regular poster I'm afraid.
Now on to the nitty gritty...
I am trying to use ServiceStack.Text to serialize objects to CSV. If I keep it simple, everything works as expected when serializing objects of a known type.
However I want to serialize many objects and I don't know the type at runtime so I am writing a reusable component where all data is treated as a System.Object. We already do this same routine for Json serialization without problems. But CsvSerializer appears to handle objects differently during serialization.
Sample code
public void TestIEnumerableObjectSerialization()
{
var data = GenerateSampleData();
JsConfig<DateTime>.SerializeFn =
time => new DateTime(time.Ticks, DateTimeKind.Utc).ToString("yyyy-MM-dd HH:mm:ss");
var csv = CsvSerializer.SerializeToCsv(data);
Console.WriteLine(csv);
Assert.Equal("DateTime\r\n"
+ "2017-06-14 00:00:00\r\n"
+ "2017-01-31 01:23:45\r\n",
csv);
}
object[] GenerateSampleData()
{
return new object[] {
new POCO
{
DateTime = new DateTime(2017,6,14)
},
new POCO
{
DateTime = new DateTime(2017,1,31, 01, 23, 45)
}
};
}
public class POCO
{
public DateTime DateTime { get; set; }
}
The result of this code is that the custom serialization function is not invoked, and the DateTime is written out using the standard ToString() method.
The cause?
The CsvWriter.Write method is inspecting the type of the records and if the type is Object it is treated as a Dictionary<string, object> and CsvDictionaryWriter generates the output.
In turn, CsvDictionaryWriter uses the ToCsvField() extension method to write each property a record.
The problem is that ToCsvField() converts the value of each property to a string using ToString() meaning no custom serialization is performed.
JsonSerializer uses TypeSerializer.SerializeToString(text) to serialize the properties of an Object using any configured custom serialization functions; but this doesn't happen with CsvSerializer.
A possible solution?
Without complicating CsvSerializer, the ToCsvField() extension method could be updated to use TypeSerializer to handle the serialization to a string. Here is what I've been testing with so far:
public static object ToCsvField(this object text)
{
var textSerialized = TypeSerializer.SerializeToString(text).StripQuotes();
return textSerialized == null || !CsvWriter.HasAnyEscapeChars(textSerialized)
? textSerialized
: string.Concat
(
CsvConfig.ItemDelimiterString,
textSerialized.Replace(CsvConfig.ItemDelimiterString, CsvConfig.EscapedItemDelimiterString),
CsvConfig.ItemDelimiterString
);
}
So far I haven't come across an issue with this change, although someone may prefer not to allocate a new intermediate variable before the return statement.
Hopefully that is enough information, so on to my questions...
Has anyone else experienced this issue?
Am I doing something wrong and should I be serializing Objects a different way?
If this is a suitable fix/implementation of TypeSerializer, what are the chances of this being addressed in an update to ServiceStack.Text? I would raise an issue on GitHub but the ServiceStack.Text repo doesn't let me raise issues.
Thanks in advance.
I have been working on an RCP Client to handle weather data.
What i do is 2 things, first i scraped the JSON i will be using and put it into a dart file. See: https://dartpad.dartlang.org/a9c1fe8ce34c608eaa28
My server.dart page, will import the weather data, and then carry out the following:
import "dart:io";
import "weather_data.dart";
import "dart:convert";
import "package:rpc/rpc.dart";
find ApiServer _apiServer = new ApiServer(prettyPrint:true);
main() async {
Weather w = new Weather(WeatherJson);
TestServer ts = new TestServer(w);
_apiServer.addApi(ts);
HttpServer server = await HttperServer.bind(InternetAddress.ANY_IP_V4, 12345);
server.listen(_apiServer.httpRequestHandler);
}
class Weather{
Map weather;
Weather(this.weather){
Map get daily => weather["daily"];
}
}
#ApiClass(name:"test_server", version: 'v1', description: 'This is a test server api to ping for some quick sample data.')
class TestServer {
Weather myWeather;
TestServer(this.myWeather){
}
#ApiMethod(method:'GET', path: 'daily')
Map<String, Object> getDaily(){
return myWeather.daily;
}
}
So, the server starts correctly, and i will go to localhost:12345/test_server/v1/daily and it will return this:
{
"summary": {},
"icon": {},
"data": {}
}
which is not correct. If you look up the JSON data, summary and icon are both strings and data is an array. They are also empty, and should contain the data i wanted to return.
Why does this occur? Is it because i am returning a Map<String, Object>? I was trying to set it up to be: Map<String, dynamic> but the dart compiler didnt like it.
How do i get this data to return the correct dataset?
The Dart website for RPC is located at: https://github.com/dart-lang/rpc
and you can see that under methods, the return value of a method can be either an instance of a class or a future. That makes sense as per usual, so I set it to be a Map<String,Object> though trying to be vague about it by saying: Map was not sufficient.
Edit:
When doing this mostly in dart pad without RPC, it seems to work correctly, by a sample of: https://dartpad.dartlang.org/3f6dc5779617ed427b75
This leads me to believe something is wrong with the Parsing tool as it seems the return type in dartpad allows to return Map, Map<String, Object>, and Map<String, dynamic>.
Having had a quick look at the RPC package README here https://pub.dartlang.org/packages/rpc, it seems that methods marked as Api methods (with #ApiMethod) should return an instance of a class with simple fields such as:
class ResourceMessage {
int id;
String name;
int capacity;
}
The RPC package will take that instance and serialize it into JSON based on the field names.
From the README:
The MyResponse class must be a non-abstract class with an unnamed
constructor taking no required parameters. The RPC backend will
automatically serialize all public fields of the the MyResponse
instance into JSON ...
You are returning a nested Map representation of the JSON you want the RPC operation to emit and would guess that the RPC package does not handle it as you are expecting it to.
Re: this from your question:
This leads me to believe something is wrong with the Parsing tool as
it seems the return type in dartpad allows to return Map, Map, and Map.
There is no 'parsing' on JSON going on on your example. The data you have is a set of nested literal Dart Maps, Lists and Strings with the same structure as the JSON it was derived from. It just happens to look like JSON.
In your example you are just selecting and printing a sub-map of your data map (data['daily']), which prints out the String that results from calling toString() - which is recursive so you get the contents of all the nested maps and lists within it.
So it's not a 'deep copy' issue, but a difference in how toString() and the RPC code processes a set of nested maps.
BTW: the return type of your getDaily() method is immaterial. What is returned is just a Map whatever the declared return type of the method is. Remember types in Dart are optional and there for editors and compilers to spot potentially incorrect code. See https://www.dartlang.org/docs/dart-up-and-running/ch02.html#variables.
I am going to piggyback off of #Argenti Apparatus here as there was a lot of information gained from him.
Long story short, the required return type of the method:
#ApiMethod(method:'GET', path: 'daily')
Map<String,Object> getDaily(){ // <-- Map<String,Object>
return myWeather.daily;
}
is the error.
I went through and updated the method signature to be Map<String,String> and it parsed it entirely correct. It did not parse the object as a string, but actually parsed it as a full recursed object.
I went through and for the sake of code cleanliness also changed signatures of Weather properties to reflect what they actually were, Map<String,Object> as well.
All in all, When defining it to be an value type of Object, it was returning curly braces, but setting it as a String parsed it correctly.
I ran it through JSLint to confirm it is correct as well.
I gave a +1 to the helper, I had to dig deeper into the code to see WHY it wasnt doing a Map correctly.
This also I feel, is plausibly a bug in RPC Dart.
I have a grails object that I am converting using def json = object as JSON. After I have it converted I want to add one more property called pin to the JSON which looks like the following.
[location:[lat:23.03, lon:72.58]]
Only way to do this so far seems like following
Serialize the DomainClass to JSON using grails.converters.json
Convert the JSON to string
Create JSONBoject using the string from Step 2
Add the property
Convert it back to String
Any other way to do this using grails.converters.json? I have tried using Gson but I do not want to go that route because I am getting many Circular Reference Errors
Try this:
domainInstance.properties + [pin: pinInstance] as JSON
I recently needed to do a similar thing. Some caveats:
This is using Grails 2.4.5
I use MongoDB as a backend. As such, I created an object marshaller for MongoDB domain classes. It is printed below, and you can wrap a similar marshaller for your domain class(es):
Marshaller:
class MongodbObjectMarshaller implements ObjectMarshaller<JSON> {
#Override
boolean supports(Object o) { return o?.properties?.dbo }
#Override
void marshalObject(Object obj, JSON converter) throws
ConverterException {
Map propertiesToOutput = obj.properties.dbo
propertiesToOutput.remove("_id") //don't print org.bson.types.ObjectId
propertiesToOutput.remove("version") //don't print gorm verson column
converter.build {
_id obj.id.toString()
propertiesToOutput.each{ entry ->
"$entry.key" entry.value
}
}
}
}
What that marshaller does, it allow in JSON output any of the domain class's properties. obj.properties.dbo is special to MongoDB, but for a regular domain class, you can just grab the properties and exclude the ones you don't need.
Then in my controller, this works:
domainInstance.pin = [location:[lat:23.03, lon:72.58]]
def content = tacticalCard as JSON
because my marshaller now picks up the pin property and prints it.
I'm currently writing a Jersey REST interface. I'm have this code which I'm trying to create the following JSON response and a list of long is been generated a array of string (Using Jaxb and Jackson)
The code looks like :
#XmlElement(name = "visitorProfiles", required = false)
private List<Long> visitorProfiles;
The JSON reponse looks like
{
"visitorProfiles":["45"]
}
And I correct JSON response should be
{
"visitorProfiles":[45]
}
This is what I'm using for the JSON configuration
context = new JSONJAXBContext(JSONConfiguration.natural().rootUnwrapping(true).build(), JerseyResources.getJaxbClasses());
Tried to reproduce the case with no success, I can't see any reason for this to happen unless the natural context wasn't apply correctly for that class