I'm really stuck with cast Rabbit response to POJO. How to do it properly? On sprin.io just no practical example.
So I'm trying to do it with this
#Bean
public DefaultClassMapper typeMapper() {
DefaultClassMapper typeMapper = new DefaultClassMapper();
Map<String, Class> idClassMapping = new HashMap<String, Class>();
idClassMapping.put("range", Loan.class);
typeMapper.setIdClassMapping(idClassMapping);
//typeMapper.setDefaultType(Loan.class);
return typeMapper;
}
#Bean
public MessageConverter messageConverter(DefaultClassMapper defaultClassMapper){
JsonMessageConverter jsonMessageConverter = new JsonMessageConverter();
jsonMessageConverter.setClassMapper(defaultClassMapper);
return jsonMessageConverter;
}
"range" actually fake value from example. Also this really doesn't work type problemn on .setIdClassMapping() . Also I can't use default mapper because serve send header without type hinting field. And I have no control on this remote server. Data format always JSON.
Caused by: org.springframework.amqp.support.converter.MessageConversionException: failed to convert Message content. Could not resolve __TypeId__ in header
Any suggestions working example for marshalling/demarshalling Java objects. I have completely different class for send back value from my code. I'm using java 8.
Just write your own ClassMapper - don't use the default one if your decision criteria to choose the class type is not compatible with its internals.
Or, you can subclass the DefaultClassMapper and override getClassIdFieldName() to tell it which message property to use.
How to change from "setLineTokenizer(new DelimitedLineTokenizer()...)" to "JsonLineMapper" in the first code below? Basicaly, it is working with csv but I want to change it to read a simple json file. I found some threads here asking about complex json but this is not my case. Firstly I thought that I should use a very diferent approach from csv way, but after I read SBiAch05sample.pdf (see the link and snippet at the bottom), I understood that FlatFileItemReader can be used to read json format.
In almost similiar question, I can guess that I am not in the wrong direction. Please, I am trying to find the simplest but elegant and recommended way for fixing this snippet code. So, the wrapper below, unless I am really obligated to work this way, seems to go further. Additionally, the wrapper seems to me more Java 6 style than my tentative which takes advantage of anonimous method from Java 7 (as far as I can judge from studies). Please, any advise is higly appreciated.
//My Code
#Bean
#StepScope
public FlatFileItemReader<Message> reader() {
log.info("ItemReader >>");
FlatFileItemReader<Message> reader = new FlatFileItemReader<Message>();
reader.setResource(new ClassPathResource("test_json.js"));
reader.setLineMapper(new DefaultLineMapper<Message>() {
{
setLineTokenizer(new DelimitedLineTokenizer() {
{
setNames(new String[] { "field1", "field2"...
//Sample using a wrapper
http://www.manning.com/templier/SBiAch05sample.pdf
import org.springframework.batch.item.file.LineMapper;
import org.springframework.batch.item.file.mapping.JsonLineMapper;
import com.manning.sbia.ch05.Product;
public class WrappedJsonLineMapper implements LineMapper<Product> {
private JsonLineMapper delegate;
public Product mapLine(String line, int lineNumber) throws Exception {
Map<String,Object> productAsMap
= delegate.mapLine(line, lineNumber);
Product product = new Product();
product.setId((String)productAsMap.get("id"));
product.setName((String)productAsMap.get("name"));
product.setDescription((String)productAsMap.get("description"));
product.setPrice(new Float((Double)productAsMap.get("price")));
return product;
}
public void setDelegate(JsonLineMapper delegate) {
this.delegate = delegate;
}
}
Really you have two options for parsing JSON within a Spring Batch job:
Don't create a LineMapper, create a LineTokenizer. Spring Batch's DefaultLineMapper breaks up the parsing of a record into two phases, parsing the record and mapping the result to an object. The fact that the incoming data is JSON vs a CSV only impacts the parsing piece (which is handled by the LineTokenizer). That being said, you'd have to write your own LineTokenizer to parse the JSON into a FieldSet.
Use the provided JsonLineMapper. Spring Batch provides a LineMapper implementation that uses Jackson to deserialize JSON objects into java objects.
In either case, you can't map a LineMapper to a LineTokenizer as they accomplish two different things.
Similar to Jersey: Json array with 1 element is serialized as object BUT on the client side. E.g. I recieve a JSON object where a field is an array regulary, but in case there is only one element, it is a single object.
{"fileInfo":[{"fileName":"weather.arff","id":"10"},"fileName":"supermarket.arff","id":"11"}]}
versus
{"fileInfo":{"fileName":"weather.arff","id":"10"}}
I'm parsing/unmarshalling the JSON using Jersey/Genson. Of course, if the JSON doesnt match the target class I recieve an error (such as expected [ but read '{' )
I've read a lot about this bug and how to avoid when creating JSON objects on the SERVER side, but I found nothing about how to handle this issus when dealing on the CLIENT side.
As always, I prefere the most codeless possibility if there are several solutions...
BTW: Moxy works but it does not marshal native Object-type objects which is another requirement...
Update
Starting with Genson 1.3 release you can achieve it by enabling permissiveParsing:
Genson genson = new GensonBuilder().usePermissiveParsing(true).create();
Answer
Uh, do you know what library produces this on server side? I am curious to see who is responsible for all those badly structured jsons out there...
It is not yet supported in Genson. Originally because IMO people should not produce such dynamic json. Anyway, I opened an issue - this can be easily done, you can expect it to be present in the release coming next week.
Otherwise here is a way to achieve it without breaking the existing mechanisms.
You need to register a Factory that will use Gensons collections factory to create an instance of its standard collection converter. Then you will wrap this converter in another one that will handle the object to array logic. Here is the code (not codeless..., but if you wait a bit you won't have to code :)).
import com.owlike.genson.convert.DefaultConverters.CollectionConverterFactory;
import com.owlike.genson.convert.DefaultConverters.CollectionConverterFactory;
class SingleObjectAsCollectionFactory implements Factory<Converter<Collection>> {
// get the default factory
Factory<Converter<Collection<?>>> defaultFactory = CollectionConverterFactory.instance;
#Override
public Converter<Collection> create(Type type, Genson genson) {
// obtain an instance of the correct default converter for this type
final CollectionConverter defaultConverter = (CollectionConverter) defaultFactory.create(type, genson);
// wrap it in your own converter
return new Converter<Collection>() {
#Override
public void serialize(Collection object, ObjectWriter writer, Context ctx) throws Exception {
defaultConverter.serialize(object, writer, ctx);
}
#Override
public Collection deserialize(ObjectReader reader, Context ctx) throws Exception {
if (reader.getValueType() == ValueType.OBJECT) {
Object object = defaultConverter.getElementConverter().deserialize(reader, ctx);
Collection result = defaultConverter.create();
result.add(object);
return result;
} else return defaultConverter.deserialize( reader, ctx );
}
};
}
}
And then register it
Genson genson = new GensonBuilder()
.withConverterFactory(new SingleObjectAsCollectionFactory())
.create();
When it comes to JSON encoding in Dart, per Seth Ladd's accouncement the finally approved now official way to go is dart:convert + JSON.Encode.
Let's say we have a bunch of model classes (PODOs) such as:
class Customer
{
int Id;
String Name;
}
Now, I'd love to be able to just JSON-encode my domain objects like this:
var customer = new Customer()
..Id = 17
..Name = "John";
var json = JSON.encode(customer);
Unfortunately, this won't work...
Uncaught Error: Converting object to an encodable object failed.
Stack Trace:
#0 _JsonStringifier.stringifyValue (dart:convert/json.dart:416)
#1 _JsonStringifier.stringify (dart:convert/json.dart:336)
#2 JsonEncoder.convert (dart:convert/json.dart:177)
....
... unless we explicitly tell dart:convert how to encode:
class Customer
{
int Id;
String Name;
Map toJson() {
Map map = new Map();
map["Id"] = Id;
map["Name"] = Name;
return map;
}
}
Do I really have to add a toJson method to every single one of my model classes, or is there a better way?
EDIT: this is the simple serialization I'm looking for:
{
"Id": 17,
"Name": "John"
}
Compare to ToJson in ServiceStack.Text, for instance.
Dart's serialization library (see Matt B's answer below) seems like a step in the right direction. However, this ...
var serialization = new Serialization()
..addRuleFor(Customer);
var json = JSON.encode(serialization.write(customer, format: new SimpleJsonFormat()));
... produces just an array with the values (no keys):
[17,"John"]
Using the default SimpleMapFormat on the other hand generates this complex representation.
Still haven't found what I'm looking for...
EDIT 2: Adding some context: I'm building a RESTful web service in Dart, and I'm looking for a JSON serialization which can easily be consumed by any client, not just another Dart client. For instance, querying the Stack Exchange API for this very question will create this JSON response. This is the serialization format I'm looking for. - Or, look at typical JSON responses returned by the Twitter REST API or the Facebook Graph API.
EDIT 3: I wrote a small blog post about this. See also the discussion on Hacker News.
IMO this is a major short-coming in Dart, surprising given its Web Application focus. I would've thought that having JSON support in the standard libraries would've meant that serializing classes to and from JSON would work like water, unfortunately the JSON support seems incomplete, where it appears the choices are to work with loosely typed maps or suffer through un-necessary boilerplate to configure your standard (PODO) classes to serialize as expected.
Without Reflection and Mirrors support
As popular Dart platforms like Flutter doesn't support Reflection/Mirrors your only option is to use a code-gen solution. The approach we've taken in ServiceStack's native support for Dart and Flutter lets you generate typed Dart models for all your ServiceStack Services from a remote URL, e.g:
$ npm install -g #servicestack/cli
$ dart-ref https://techstacks.io
Supported in .NET Core and any of .NET's popular hosting options.
The example above generates a Typed API for the .NET TechStacks project using the generated DTOs from techstacks.io/types/dart endpoint. This generates models following Dart's JsonCodec pattern where you can customize serialization for your Dart models by providing a fromJson named constructor and a toJson() instance method, here's an example of one of the generated DTOs:
class UserInfo implements IConvertible
{
String userName;
String avatarUrl;
int stacksCount;
UserInfo({this.userName,this.avatarUrl,this.stacksCount});
UserInfo.fromJson(Map<String, dynamic> json) { fromMap(json); }
fromMap(Map<String, dynamic> json) {
userName = json['userName'];
avatarUrl = json['avatarUrl'];
stacksCount = json['stacksCount'];
return this;
}
Map<String, dynamic> toJson() => {
'userName': userName,
'avatarUrl': avatarUrl,
'stacksCount': stacksCount
};
TypeContext context = _ctx;
}
With this model you can use Dart's built-in json:convert APIs to serialize and deserialize your model to JSON, e.g:
//Serialization
var dto = new UserInfo(userName:"foo",avatarUrl:profileUrl,stacksCount:10);
String jsonString = json.encode(dto);
//Deserialization
Map<String,dynamic> jsonObj = json.decode(jsonString);
var fromJson = new UserInfo.fromJson(jsonObj);
The benefit of this approach is that it works in all Dart platforms, including Flutter and AngularDart or Dart Web Apps with and without Dart 2’s Strong Mode.
The generated DTOs can also be used with servicestack's Dart package to enable an end to end typed solution which takes care JSON serialization into and out of your typed DTOs, e.g:
var client = new JsonServiceClient("https://www.techstacks.io");
var response = await client.get(new GetUserInfo(userName:"mythz"));
For more info see docs for ServiceStack's native Dart support.
Dart with Mirrors
If you're using Dart in a platform where Mirrors support is available I've found using a Mixin requires the least effort, e.g:
import 'dart:convert';
import 'dart:mirrors';
abstract class Serializable {
Map toJson() {
Map map = new Map();
InstanceMirror im = reflect(this);
ClassMirror cm = im.type;
var decls = cm.declarations.values.where((dm) => dm is VariableMirror);
decls.forEach((dm) {
var key = MirrorSystem.getName(dm.simpleName);
var val = im.getField(dm.simpleName).reflectee;
map[key] = val;
});
return map;
}
}
Which you can mixin with your PODO classes with:
class Customer extends Object with Serializable
{
int Id;
String Name;
}
Which you can now use with JSON.encode:
var c = new Customer()..Id = 1..Name = "Foo";
print(JSON.encode(c));
Result:
{"Id":1,"Name":"Foo"}
Note: see caveats with using Mirrors
I wrote the Exportable library to solve such things like converting to Map or JSON. Using it, the model declaration looks like:
import 'package:exportable/exportable.dart';
class Customer extends Object with Exportable {
#export int id;
#export String name;
}
And if you want to convert to JSON, you may:
String jsonString = customer.toJson();
Also, it's easy to initialize new object from a JSON string:
Customer customer = new Customer()..initFromJson(jsonString);
Or alternatively:
Customer customer = new Exportable(Customer, jsonString);
Please, see the README for more information.
An alternative is to use the Serialization package and add rules for your classes. The most basic form uses reflection to get the properties automatically.
Redstone mapper is the best serialization library I've used. JsonObject and Exportable have the downside that you have to extend some of their classes. With Redstone Mapper you can have structures like this
class News
{
#Field() String title;
#Field() String text;
#Field() List<FileDb> images;
#Field() String link;
}
It works with getters and setters, you can hide information by not annotating it with #Field(), you can rename field from/to json, have nested objects, it works on the server and client. It also integrates with the Redstone Server framework, where it has helpers to encode/decode to MongoDB.
The only other framework I've seen thats on the right direction is Dartson, but it still lack some features compared to Redstone Mapper.
I have solved with:
class Customer extends JsonObject
{
int Id;
String Name;
Address Addr;
}
class Address extends JsonObject{
String city;
String State;
String Street;
}
But my goal is bind data from/to json from/to model classes; This solution work if you can modify model classes, in a contrast you must use solution "external" to convert model classes;
see also: Parsing JSON list with JsonObject library in Dart
Another package solving this problem is built_value:
https://github.com/google/built_value.dart
With built_value your model classes look like this:
abstract class Account implements Built<Account, AccountBuilder> {
static Serializer<Account> get serializer => _$accountSerializer;
int get id;
String get name;
BuiltMap<String, JsonObject> get keyValues;
factory Account([updates(AccountBuilder b)]) = _$Account;
Account._();
}
Note that built_value isn't just about serialization -- it also provides operator==, hashCode, toString, and a builder class.
I have achieve with this:
To make this work, pass explicitToJson: true in the #JsonSerializable() annotation over the class declaration. The User class now looks as follows:
import 'address.dart';
import 'package:json_annotation/json_annotation.dart';
part 'user.g.dart';
#JsonSerializable(explicitToJson: true)
class User {
String firstName;
Address address;
User(this.firstName, this.address);
factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
Map<String, dynamic> toJson() => _$UserToJson(this);
}
You can check here: https://flutter.dev/docs/development/data-and-backend/json#generating-code-for-nested-classes
I prefer using https://ashamp.github.io/jsonToDartModel/ online tool write by myself.
It has features below:
online use, without plugin
support multidimensional list
support complex json
support convert all props to String type
empty props warning
single file
dart keyword protected
instant convert
I think it's better than other tools.Welcome if you have any suggestion, issue or bug report.
Some of the answers are no longer applicable to Flutter 2; here is the process for automatically creating toJson and fromJson methods:
https://flutter.dev/docs/development/data-and-backend/json#creating-model-classes-the-json_serializable-way
PS: I wish this would be as simple as using Newtonsoft library in Asp.Net, this solution is closest to an automated solution
I'm trying, for the first time, to parse json in gwt and it's not working. Since I'm a newbie this might be some obvious stupid mistake. The array is not retrieved correctly.
This is the piece of code on which I'm debugging:
String json = "{\"lokacije\":[{\"sifraLokacije\":1,\"nazivLokacije\":\"Policijska stanica\",\"brojDokumenata\":70}],\"status\":1}";
LocationsResponse locationsResponse = createLocationsResponse("("+json+")");
// this is ok, status is 1
int status = locationsResponse.getStatus();
// length of this array is 0 and you can see from json that it has one element (the same if it has more)
int brojLokacija = locationsResponse.getLokacije().length();
...
private final native LocationsResponse createLocationsResponse(String json) /*-{
return eval(json);
}-*/;
LocationsResponse class:
public class LocationsResponse extends JavaScriptObject {
protected LocationsResponse() {}
public final native int getStatus() /*-{ return this.status; }-*/;
public final native JsArray<JSOLokacija> getLokacije() /*-{ this.lokacije; }-*/;
}
JSOLokacija class:
public class JSOLokacija extends JavaScriptObject {
protected JSOLokacija() {} ;
public final native int getSifraLokacije() /*-{ this.sifraLokacije; }-*/;
public final native String getNazivLokacije() /*-{ this.nazivLokacije; }-*/;
public final native int getBrojDokumenata() /*-{ this.brojDokumenata; }-*/;
}
Second edit: Wow, I'm just useless today. My first answer returned JSONValue, which is pretty annoying if you want to work with a JSO.
Edit: Aaand just noticed your comment that you fixed it... Still, using the provided tools will tend to help prevent you from getting into annoying situations like this.
Here is another tool you should be aware of, esp if you are after using JSON, and not just objects from JS: AutoBeans (http://code.google.com/p/google-web-toolkit/wiki/AutoBean) - with these, you don't need to write out the JSNI code, just define the properties you expect to have, and it will work out all the wrapper code.
First, mostly useless answer:
eval doesn't work like that - it is meant to run JS, not turn JSON into data, and a json expression (also a js expression) isn't a legal statement in Javascript. Adding the "(" and ")" around the content is why it is working at all, but this is somewhat risky - usually it is better to trust the browser to do it right if possible:
Use JSONParser.parseStrict (or parseLenient if you expect parsing errors, but are absolutely certain that no possible attacks could be coming from there - this will end up calling eval for you, but this way you dont have to maintain it) instead to make sure the content is safe, and to parse it to js correctly. To turn this into a JSO then, you call .isObject().getJavaScriptObject() on the result of the parse method, which you then have to .cast() to the right value.