I have a Camel ReST route that uses Jackson to convert a collection to JSON but it's throwing an error when the object in the collection includes a LocalDate (everything works fine without LocalDates).
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Java 8 date/time type java.time.LocalDate not supported by default: add Module "com.fasterxml.jackson.datatype:jackson-datatype-jsr310"
I have added a class to customise the Quarkus ObjectMapper:
#Singleton
class MyObjectMapperCustomizer : ObjectMapperCustomizer {
override fun customize(objectMapper: ObjectMapper) {
objectMapper.registerModule(JavaTimeModule())
}
}
but it looks like Camel is not using this ObjectMapper and I can see in VisualVM that there are 3 instances of the ObjectMapper class.
The Camel rest endpoint that's throwing the exception is:
.get().produces(MediaType.APPLICATION_JSON).route()
.bean(svc.getAllTradeList()).marshal().json(JsonLibrary.Jackson).endRest()
The svc.getAllTradeList just sets the exchange body to a list of Trade objects and the Trade object itself is pretty basic:
#RegisterForReflection
data class Trade(
val id: String,
val description: String,
val notional: Double,
val tradeDate: LocalDate
)
I can't see an obvious way to make Camel use the Quarkus ObjectMapper that I'm customising or to customise the one that Camel appears to be creating.
Any pointers would be much appreciated.
If there are multiple instances of the object mapper, then camel does not know which one to pick so to use it, you have to explicit configure what camel should use:
If the object mapper from quarkus is named, you can do something like:
.marshal()
.json()
.libray(JsonLibrary.Jackson)
.objectMapper("name-of-the-object-mapper")
if not, you can create an instance of the JacksonDataFormat and configure it:
JacksonDataFormat df = new JacksonDataFormat();
df.setObjectMapper(mapper) // use CDI to get a referece
And then use it directly:
.marshal(mapper)
Related
i am getting error - This class does not have constructor at object : TypeToken<List<Todo>>() + object is not abstract and does not implement object member
data class Todo(
val identifier: Long ,
val name: String ,
val description: String
)
class DefaultData {
private lateinit var myService: MyService
#PostConstruct
fun initializeDefault() {
val fileContent = this::class.java.classLoader.getResource("example.json").readText()
val todos: List<Todo> = Gson().fromJson(fileContent, object : TypeToken<List<Todo>>() {}.type)
myService.createTodoFromJsontodos
}
}
how can I fix this?
Objective is : To be able to create an endpoint that can get data from json file via service
Is there is a full fledged example
Also how to create interfaces in Ktor? As I want to use Dependency Inversion to enable retrieving data from different sources
Kotlin has built-in util similar to TypeToken, so I suggest using it instead:
Gson().fromJson(fileContent, typeOf<List<Todo>>().javaType)
You will need to add a dependency to kotlin-reflect. typeOf() function is marked as experimental, but I use it for some time already and never had any problems with it.
Also, you said in your comment that this is a starter project. If you don't have any existing code already then I suggest to use kotlinx-serialization instead of Gson. It is a de facto standard in Kotlin.
You can easily take advantage of kotlinx-serialization.
Steps:
Add the kotlin serialization plugin in your build.gradle file
kotlin("plugin.serialization") version "1.5.20"
plugins {
application
java
id("org.jetbrains.kotlin.jvm") version "1.5.21"
kotlin("plugin.serialization") version "1.5.20"
}
Add the dependecy for serialization library
dependencies {
...
implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.2.2")
}
Decode your json string to corresponding object using Json decode method
val JSON = Json {isLenient = true}
val mytodos = JSON.decodeFromString(message) as List<Todo>
In Kotlin, a common use for object is using it for singletons, like:
object MyObject {
...
}
However, when using micronaut framework, the official documentation recommends using something like this:
#Singleton
class V8Engine : Engine {
override var cylinders = 8
override fun start(): String {
return "Starting V8"
}
}
Why can't I use simply object instead of using annotation #Singleton with a class?
With a #Singleton, Micronaut can automatically manage dependencies between beans. If you go with the other class in https://docs.micronaut.io/latest/guide/ioc.html#beans, translated to Kotlin:
#Singleton
class Vehicle(private val engine: Engine) {
public fun start() = engine.start()
}
It can't be just an object because takes a parameter.
This parameter is discovered by Micronaut to be the singleton instance of V8Engine, which needs that to be a #Singleton and not an object.
Of course, in this case you could just directly use V8Engine in Vehicle; but it's easier to change e.g. if you want Engine not to be a singleton anymore.
Why can't I use simply object instead of using annotation #Singleton
with a class?
You can use object instead of using #Singleton with a class. Micronaut won't manage instances for you, but that is allowed.
If I try to deserialize below type stored as String:
List<Entry<String, String>> entryList;
where entryList contains:
[{"dummyKey1":"dummyValue1"}]
I get the following errors
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of java.util.Map$Entry, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information.
I get above error while running a test case in junit, but if I remove the test case, then after deploying everything runs fine :
Above error comes while running junit test case because of absence of NoArgsConstructor in Entry. So, I created a DummyEntry with NoArgsConstructor that calls Entry with arguments as null.
DummyEntry<K, V> extends SimpleEntry<K, V>
After making this change, above error didn't come but I started getting below error after changes are deployed.
Caused by: com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException:
Unrecognized field "dummyKey1", not marked as ignorable (2 known properties: "value", "key"]).
What is the reason that one way doesn't works for junit, but in production it works while other does work in junit but not in production.
Also, I noticed one additional thing: In production, Map.Entry is serialized to
{'dummyKey1':'dummyValue1'}
whereas, test case in junit serializes the same string as
{'key':'dummyKey1', 'value':'dummyValue1'}
What is the reason about this weird behavior ? How can I make this thing work for both ?
I suspect you might be encountering an issue with different serialisation strategies for Map.Entry.
In v2.5.0 (IIRC) of jackson-databind Map.Entry was supported as a 'known type'. Prior to this version, the key and value attributes of Map.Entry would appear in a serialised Map.Entry. After this version, that's no longer the case.
Here are some example test cases showing what I mean:
#Test
public void mapSerialisationPreJackson2_5_0() throws IOException {
Map<String, String> aMap = Maps.newHashMap();
aMap.put("dummyKey1", "dummyValue1");
Set<Map.Entry<String, String>> incoming = aMap.entrySet();
ObjectMapper objectMapper = new ObjectMapper();
String serialised = objectMapper.writeValueAsString(incoming);
// prints: [{"key":"dummyKey1","value":"dummyValue1"}]
System.out.println(serialised);
Set<Map.Entry<String, String>> deserialised = objectMapper.readValue(serialised, Set.class);
// prints: [{key=dummyKey1, value=dummyValue1} (just like you posted in your question) whereas for versions > 2.5.0 the serialised form is ]
System.out.println(deserialised);
}
#Test
public void mapSerialisationPostJackson2_5_0() throws IOException {
Map<String, String> aMap = Maps.newHashMap();
aMap.put("dummyKey1", "dummyValue1");
Set<Map.Entry<String, String>> incoming = aMap.entrySet();
ObjectMapper objectMapper = new ObjectMapper();
String serialised = objectMapper.writeValueAsString(incoming);
// prints: [{"dummyKey1":"dummyValue1"}]
System.out.println(serialised);
Set<Map.Entry<String, String>> deserialised = objectMapper.readValue(serialised, Set.class);
// prints: [{dummyKey1=dummyValue1}]
System.out.println(deserialised);
}
Prior to v2.5.0 a Map.Entry would be serialised to {key=dummyKey1, value=dummyValue1} (just like you posted in your question) whereas for versions > 2.5.0 the serialised form is {dummyKey1=dummyValue1}.
I think you are using a version of jackson-databind in your test context which is < 2.5.0 and a version of jackson-databind in your production context which is > 2.5.0
In order to be able to deserialize [{"dummyKey1":"dummyValue1"}] into a List<Entry<String, String>> variable you can:
Use Jackson's parameter names module. Read more here. It basically allows non-annotated, non default constructors with parameters to be used for deserialization of a class. In this case the constructors of the various implementations of Map.Entry. A perfectly straightforward solution if you use Java 8 anyway.
If you can't use the parameter names module (e.g. Java 7), you can look into using mixins to annotate a constructor of a class without modifying it's source code. I had a go at that and it's tricky. For HashMap for instance the implementation of Map.Entry is Node which has package private visibility.
I am trying to deserialize a Json string into an object of type OperationResult<String> using Jackson with Kotlin.
I need to construct a type object like so:
val mapper : ObjectMapper = ObjectMapper();
val type : JavaType = mapper.getTypeFactory()
.constructParametricType(*/ class of OperationResult */,,
/* class of String */);
val result : OperationResult<String> = mapper.readValue(
responseString, type);
I've tried the following but they do not work.
val type : JavaType = mapper.getTypeFactory()
.constructParametricType(
javaClass<OperationResult>,
javaClass<String>); // Unresolved javaClass<T>
val type : JavaType = mapper.getTypeFactory()
.constructParametricType(
OperationResult::class,
String::class);
How do I get a java class from the type names?
You need to obtain instance of Class not KClass. To get it you simply use ::class.java instead of ::class.
val type : JavaType = mapper.typeFactory.constructParametricType(OperationResult::class.java, String::class.java)
Kotlin has a few things that become a concern when using Jackson, GSON or other libraries that instantiate Kotlin objects. One, is how do you get the Class, TypeToken, TypeReference or other specialized class that some libraries want to know about. The other is how can they construct classes that do not always have default constructors, or are immutable.
For Jackson, a module was built specifically to cover these cases. It is mentioned in #miensol's answer. He shows an example similar to:
import com.fasterxml.jackson.module.kotlin.* // added for clarity
val operationalResult: OperationalResult<Long> = mapper.readValue(""{"result":"5"}""")
This is actually calling an inline extension function added to ObjectMapper by the Kotlin module, and it uses the inferred type of the result grabbing the reified generics (available to inline functions) to do whatever is needed to tell Jackson about the data type. It creates a Jackson TypeReference behind the scenes for you and passes it along to Jackson. This is the source of the function:
inline fun <reified T: Any> ObjectMapper.readValue(content: String): T = readValue(content, object: TypeReference<T>() {})
You can easily code the same, but the module has a larger number of these helpers to do this work for you. In addition it handles being able to call non-default constructors and static factory methods for you as well. And in Jackson 2.8.+ it also can deal more intelligently with nullability and default method parameters (allowing the values to be missing in the JSON and therefore using the default value). Without the module, you will soon find new errors.
As for your use of mapper.typeFactory.constructParametricType you should use TypeReference instead, it is much easier and follows the same pattern as above.
val myTypeRef = object: TypeReference<SomeOtherClass>() {}
This code creates an anonymous instance of a class (via an object expression) that has a super type of TypeRefrence with your generic class specified. Java reflection can then query this information.
Be careful using Class directly because it erases generic type information, so using SomeOtherClass::class or SomeOtherClass::class.java all lose the generics and should be avoided for things that require knowledge of them.
So even if you can get away with some things without using the Jackson-Kotlin module, you'll soon run into a lot of pain later. Instead of having to mangle your Kotlin this module removes these types of errors and lets you do things more in the "Kotlin way."
The following works as expected:
val type = mapper.typeFactory.constructParametricType(OperationalResult::class.java, String::class.java)
val operationalResult = mapper.readValue<OperationalResult<String>>("""{"result":"stack"}""", type)
println(operationalResult.result) // -> stack
A simpler alternative to deserialize generic types using com.fasterxml.jackson.core.type.TypeReference:
val operationalResult = mapper.readValue<OperationalResult<Double>>("""{"result":"5.5"}""",
object : TypeReference<OperationalResult<Double>>() {})
println(operationalResult.result) // -> 5.5
And with the aid of jackson-kotlin-module you can even write:
val operationalResult = mapper.readValue<OperationalResult<Long>>("""{"result":"5"}""")
println(operationalResult.result)
Is there a way to use Parceler with Kotlin data classes and constructor for serialization without using #ParcelProperty annotation for each field?
If I try and use library like this:
#Parcel
data class Valve #ParcelConstructor constructor(val size: Int)
I get Error:Parceler: No corresponding property found for constructor parameter arg0. But if I add #ParcelProperty("size") it works just fine.
Why is that?
Update:
There are other another way to use this library.
I could just remove #ParcelConstructor annotation, but then I will get error
Error:Parceler: No #ParcelConstructor annotated constructor and no default empty bean constructor found.
I think (haven't tested it) I also could make all constructor parameters optional and add #JvmOverloads but that has a side effect that I have to check all properties of the class if they are null or not.
Update 2:
This is what worked for me:
#Parcel
data class Valve(val size: Int? = null)
In short generated Java class must have default empty constructor. One way to achieve that is to do as above - all variables should have default values.
According to the docs, Parceler by default works with public fields. But a usual Kotlin data class (as in your example) is rather a "traditional getter/setter bean", since every Kotlin property is represented by a private field and a getter/[setter].
TL; DR: I think this will work:
#Parcel(Serialization.BEAN)
data class Valve(val size: Int = 10)
Note the default value, it allows Kotlin to automatically generate an additional empty constructor, which is required by the Java Been specification.
Another way would be to mark the constructor that we already have:
#Parcel(Serialization.BEAN)
data class Driver #ParcelConstructor constructor(val name: String)
The specific document: https://github.com/johncarl81/parceler#gettersetter-serialization
I know this question already has an answer, but for future viewers who are also struggling to get Parceler to work with kotlin data objects, I wrote a new annotation processor to generate the Parcelable boilerplate for Kotlin data classes. It's designed to massively reduce the boilerplate code in making your data classes Parcelable:
https://github.com/grandstaish/paperparcel
Usage:
Annotate your data class with #PaperParcel, implement PaperParcelable, and add a JVM static instance of the generated CREATOR e.g.:
#PaperParcel
data class Example(
val test: Int,
...
) : PaperParcelable {
companion object {
#JvmField val CREATOR = PaperParcelExample.CREATOR
}
}
Now your data class is Parcelable and can be passed directly to a Bundle or Intent
Edit: Update with latest API
Just add the default constructor:
#Parcel
data class Valve(val size: Int) {
constructor() : this(0)
}
if you use Kotlin 1.1.4 or above it's easier to use #Parcelize annotation
For doing this first add this to build.gradle
android {
//other codes
//for using latest experimental build of Android Extensions
androidExtensions {
experimental = true
}
}
Then change your class like this
#Parcelize
data class Valve(val size: Int? = null) : Parcelable