I'm trying to create a Json object using Jackson but I can't use put because it's deprecated and will fail the pipelines checks in my company so I'm trying to use set:
fun HttpRequest.toJSONString(): String {
val mapper = ObjectMapper()
val root = mapper.createObjectNode()
val headers = mapper.createObjectNode()
this.headers().map().entries.forEach {h ->
headers.put(h.key, mapper.convertValue(h.value, JsonNode::class.java)) // its deprecated
}
root.set("headers", headers) // its failing
root.set("url_path", "https://facebook.com") // fails
return root.toString()
}
I got an error message: Not enough information to infer parameter T in operator fun <T : JsonNode!> set(p0: String!, p1: JsonNode!): T!
Please specify it explicitly.
How can I solve it?
I would advise you to try something more like that:
fun HttpRequest.toJSONString() =
ObjectMapper().writeValueAsString(
this.headers
.put("url_path", listOf("https://facebook.com"))
// put the rest here
)
It is usually inconvenient to deal directly with the Node objects and they are protected. I would strongly advise you to write your whole objects in kotlin and then use writeValueAsString from the ObjectMapper.
Use put when the value is a string (that version of the method is not deprecated). Use replace when the value is a JsonNode, or, if you want to chain the invocations together use set with a type parameter. Code to demonstrate:
val mapper = ObjectMapper()
val root = mapper.createObjectNode()
val headers = mapper.createObjectNode()
headers.put("key", "value") // Use put when the value is a primitive
root.replace("headers", headers) // Use replace for objects
root.set<JsonNode>("headers", headers) // Or use set with a type parameter
root.put("url_path", "https://facebook.com")
return root.toString()
Related
I am trying to use the public interface Function (as I learned it in Java) in Kotlin.
For this I created my method
fun foo(input: List<String>, modifier1: Function<List<String>>? = null){
}
as far I remember here I should be able to do modifier1.apply(input)
but seems like it is not possible (it is possible to do modifier1.apply{input} though)
Reading more about it I found this:
Kotlin: how to pass a function as parameter to another?
So I changed my method signature to this:
fun foo(input:String, modifier2: (List<String>) -> (List<String>){
}
Here I am able to do modifier2(input)
and I can call foo this way
service.foo(input, ::myModifierFunction)
where
fun myModifierFunction(input:List<String>):List<String>{
//do something
return input
}
So far this seems possible but it is not acceptable to have the function reference as nullable, is there any way I can do that? or use Function ?
You were using kotlin.Function instead of java.util.function.Function in your first example. Note that the latter takes 2 generic types: 1 for the incoming parameter and 1 for the resulting one.
The apply method you saw is the default Kotlin one: apply, not the one of Java's Function-interface.
If you really want to have the Java-function as nullable type the following should work:
fun foo(input: List<String>, modifier1: java.util.function.Function<List<String>, List<String>>? = null) {
modifier1?.apply(input) ?: TODO("what should be done if there wasn't passed any function?")
}
Kotlin variant for the same:
fun foo(input: List<String>, modifier1: ((List<String>) -> List<String>)? = null) {
modifier1?.invoke(input) ?: TODO("what should be done if there wasn't passed any function?")
}
Maybe also a default function, such as { it } instead of null might better suite your needs? (Java variant would be Function.identity()):
// java modifier1 : Function<List<String>, List<String>> = Function.identity()
// kotlin modifier1 : (List<String>) -> List<String> = { it }
You can make the reference nullable simply with ? — the only wrinkle is that the whole function type needs to be in parens first:
fun foo(input: String, modifier2: ((List<String>) -> List<String>)? = null) {
}
As required, modifier2 is optional; if specified, it may contain null, or it may contain a function taking and returning a list of strings.
As mentioned in another answer, kotlin.Function is not the same as java.util.function.Function — though in practice you shouldn't need to refer to either directly, as the -> notation is simpler.
If you want to pass in a function that takes List<String> as its parameter and returns nothing meaningful, the type for you is Function1<List<String>, Unit>. The method name for invoking a function is invoke(), which you could also do with just regular parentheses, if it wasn't nullable. All in all, your code could look something like this:
fun foo(input: List<String>, modifier1: Function1<List<String>, Unit>? = null) {
modifier1?.invoke(input)
}
The 1 in the typename of Function1 means that it's a one parameter function, there's also Function0, Function2, etc.
The Function type on its own is not something you can use to call that function, as it's an empty marker interface. All functions implement this regardless of how many parameters they have.
I'm posting json array of objects. I'm trying to parse it in code like this
val objs = call.receive<List<MyClass>>() // this work fine
val name objs[0].name // this throw exception LinkedTreeMap cannot be cast to MyClass
In above code second line throws exception com.google.gson.internal.LinkedTreeMap cannot be cast to MyClass
If i post simple object and parse it in ktor with call.receive<MyClass>() then it will work fine. So issue is only when parsing list of objects.
Using your code with Array instead of List worked for me using ktor v1.2.3:
val objs = call.receive<Array<MyClass>>()
val name = objs[0].name
Side Note:
I later changed my data class to this format to help with mapping from database rows to a data class (i.e. to use BeanPropertyRowMapper). I don't remember this having an effect on de/serialization, but if the first part still isn't working for you, you may try this...
data class MyClass(
var id: Int? = null,
var name: String? = null,
var description: String? = null,
)
Reference: Kotlin data class optional variable
You can do like this
val json = call.receive<String>()
val objs = Gson().fromJson(json, Array<MyClass>::class.java)
objs[0].name
Updated
You can also create extention function for that like this
suspend inline fun <reified T> ApplicationCall.safeReceive(): T {
val json = this.receiveOrNull<String>()
return Gson().fromJson(json, T::class.java)
}
then use it like this
val objs = call.safeReceive<Array<MyClass>>()
objs[0].name
Is it possible to create extension of final classes like String? Like in swift it is possible to add additional methods inside a extension of final class.
For an example - I would like to create a method in String extension which will tell me String have valid length for password.
val password : String = mEdtPassword!!.getText().toString()
// how to define haveValidLength method in extension
val isValid : Boolean = password.haveValidLength()
Note - That example is just for a sake to understand usability of extension, not a real scenario.
yes, you can. Kotin extension method provides the ability to extend a class with new functionality without having to inherit from the class or use any type of design pattern such as Decorator.
Below is an extension method for a String:
// v--- the extension method receiver type
fun String.at(value: Int) = this[value]
And the extension method code generated as Java below:
public static char at(String receiver, int value){
return receiver.charAt(value);
}
So an extension method in Kotlin is using delegation rather than inheritance.
Then you can calling an extension method like as its member function as below:
println("bar".at(1))//println 'a'
You also can write an extension method for the existing extension function, for example:
fun String.substring(value: Int): String = TODO()
// v--- throws exception rather than return "ar"
"bar".substring(1)
But you can't write an extension method for the existing member function, for example:
operator fun String.get(value: Int): Char = TODO()
// v--- return 'a' rather than throws an Exception
val second = "bar"[1]
Trying to add more detail, this answer might be helpful for someone.
Yes we can add additional methods to final classes like String. For an example I would like to add one method in String which will tell me that my String have valid number of characters for password or not.
So what I have to do is, I have ti create a below function which can be written in same class or at different separate class file.
fun String.hasValidPassword() : Boolean {
// Even no need to send string from outside, use 'this' for reference of a String
return !TextUtils.isEmpty(this) && this.length > 6
}
And now from anywhere call
val isValid : Boolean = password.haveValidLength()
Suggestion
If your application just has a single password validation, then there is no problem.
However, I don't suggest you write such a extension method hasValidPassword if the application has more than one validation. since the extension method is satically, you can't change your hasValidPassword in runtime. So if you want to change the validation in runtime, you should using a function instead, for example:
class PasswordRepository(private val validate:(String)->Boolean){
fun save(value:String){
if(validate(value)){
//TODO persist the password
}
}
}
val permitAll = PasswordRepository {true}
val denyAll = PasswordRepository {false}
permitAll.save("it will be persisted")
denyAll.save("it will not be persisted")
In other words, the extension method above violates Single Responsibility Principle, it does validation & string operations.
You can do that with extension functions in Kotlin. With extensions, you are able to add extra functionality to a class that you do or do not have access to; for example a legacy code base. In the example given in the Kotlin docs here, swap was added to MutableList<Int> which doesn't have swap originally. A this keyword is used that refers to the object that the swap functionality will operate on. In the example below, this refers to testList
val testList = mutableListOf(1, 2, 3)
testList.swap(0, 2)
I have a Kotlin data class that I am constructing with many immutable properties, which are being fetched from separate SQL queries. If I want to construct the data class using the builder pattern, how do I do this without making those properties mutable?
For example, instead of constructing via
var data = MyData(val1, val2, val3)
I want to use
builder.someVal(val1)
// compute val2
builder.someOtherVal(val2)
// ...
var data = builder.build()
while still using Kotlin's data class feature and immutable properties.
I agree with the data copy block in Grzegorz answer, but it's essentially the same syntax as creating data classes with constructors. If you want to use that method and keep everything legible, you'll likely be computing everything beforehand and passing the values all together in the end.
To have something more like a builder, you may consider the following:
Let's say your data class is
data class Data(val text: String, val number: Int, val time: Long)
You can create a mutable builder version like so, with a build method to create the data class:
class Builder {
var text = "hello"
var number = 2
var time = System.currentTimeMillis()
internal fun build()
= Data(text, number, time)
}
Along with a builder method like so:
fun createData(action: Builder.() -> Unit): Data {
val builder = Builder()
builder.action()
return builder.build()
}
Action is a function from which you can modify the values directly, and createData will build it into a data class for you directly afterwards.
This way, you can create a data class with:
val data: Data = createData {
//execute stuff here
text = "new text"
//calculate number
number = -1
//calculate time
time = 222L
}
There are no setter methods per say, but you can directly assign the mutable variables with your new values and call other methods within the builder.
You can also make use of kotlin's get and set by specifying your own functions for each variable so it can do more than set the field.
There's also no need for returning the current builder class, as you always have access to its variables.
Addition note: If you care, createData can be shortened to this:
fun createData(action: Builder.() -> Unit): Data = with(Builder()) { action(); build() }.
"With a new builder, apply our action and build"
I don't think Kotlin has native builders. You can always compute all values and create the object at the end.
If you still want to use a builder you will have to implement it by yourself. Check this question
There is no need for creating custom builders in Kotlin - in order to achieve builder-like semantics, you can leverage copy method - it's perfect for situations where you want to get object's copy with a small alteration.
data class MyData(val val1: String? = null, val val2: String? = null, val val3: String? = null)
val temp = MyData()
.copy(val1 = "1")
.copy(val2 = "2")
.copy(val3 = "3")
Or:
val empty = MyData()
val with1 = empty.copy(val1 = "1")
val with2 = with1.copy(val2 = "2")
val with3 = with2.copy(val3 = "3")
Since you want everything to be immutable, copying must happen at every stage.
Also, it's fine to have mutable properties in the builder as long as the result produced by it is immutable.
It's possible to mechanize the creation of the builder classes with annotation processors.
I just created ephemient/builder-generator to demonstrate this.
Note that currently, kapt works fine for generated Java code, but there are some issues with generated Kotlin code (see KT-14070). For these purposes this isn't an issue, as long as the nullability annotations are copied through from the original Kotlin classes to the generated Java builders (so that Kotlin code using the generated Java code sees nullable/non-nullable types instead of just platform types).
I have received a JavaScript object in response to a remote HTTP request. I have a kotlin model (trait) that defines the various fields I expect on the object (the nullable ones are optional).
First, I want to do an is check to make sure my object is in fact of the expected type. I initially tried payload is MyModel but that doesn't work due to the way the is operator is written in kotlin.js.
Second, I want to cast to MyModel so I can get auto-complete, etc. on the object while I work with it. Normally, the is alone would be enough but since that doesn't work I need something for this problem as well.
I would like to avoid manually populating my object from a dynamic. I wouldn't mind doing this so much if I could use by Delegates.mapVal(...) but that requires a Map<String, Any?> and I don't know how to get my dynamic/Any? payload into a Map<String, Any?>.
1) We don't have structure check for is in performance reasons.
I don't sure that we need generic solution for this, but anyway I created issue about it, feel free to vote or star it to get updates.
2) is enough if you use smart cast, like:
if (payload is MyModel) {
// call MyModel members on payload
}
But don't forget about (1) :)
3) You can write something like:
class MapDynamic<out V>(val d: dynamic) {
public fun get(thisRef: Any, desc: PropertyMetadata): V {
return d[desc.name]
}
}
class Foo(data: dynamic) {
val field: Int by MapDynamic(data)
}
fun main(args : Array<String>) {
val f = Foo(object { val field = 123 })
println(f.field)
}
But it looks too verbose, but You can add additional logic for e.g. when data don't have requested field. And if You don't need custom logic I think cast is enough.
For the second part, the cast, you can do:
fun responseHandler(payload: dynamic) {
val myModel = payload as MyModel
}
or
fun responseHandler(payload: dynamic) {
val myModel: MyModel = payload
}
This will throw an NPE if payload is null, but it won't actually validate that the payload matches MyModel. In particular, you may end up with null fields/properties that shouldn't be if the payload was missing those fields/properties.