Serializing a Map with custom MapAdapter in moshi - serialization

I am trying to write a custom MapAdapter in moshi My requirement is to ignore any bad elements in the map. I have successfully written deserialization method(fromJson()), however, I am facing trouble with toJson. here is my toJson() method.
override fun toJson(writer: JsonWriter, value: Map<Any?, Any?>?) {
if (value == null) {
writer.nullValue()
} else {
writer.beginObject()
value.forEach {
writer.name(elementKeyAdapter.toJsonValue(it.key).toString())
.value(elementValueAdapter.toJson(it.value))
}
writer.endObject()
}
}
problem with this code is that it always is writing values in map as string in final Json. For example consider this code
enum class VehicleType2 {
#Json(name ="type1")
TYPE1,
#Json(name ="type2")
TYPE2,
#Json(name ="type3")
TYPE3,
#Json(name ="type4")
TYPE4,
}
and
val map = mutableMapOf<VehicleType2, Int>()
map[VehicleType2.TYPE1] = 1
map[VehicleType2.TYPE2] = 2
val adapter: JsonAdapter<Map<VehicleType2, Int>> =
moshi.adapter(Types.newParameterizedType(Map::class.java, VehicleType2::class.java, Integer::class.java))
Log.i("test", adapter.toJson(map))
this results in following Json
{"type1":"1","type2":"2"}
notice how 1 and 2 are strings and not integers. I have tried many permutations bit no success so far.
Here is more complete sample which reproduces this issue.

After few more trials and errors I found that this is working fine
writer.name(elementKeyAdapter.toJsonValue(it.key).toString())
elementValueAdapter.toJson(writer, it.value)
instead of
writer.name(elementKeyAdapter.toJsonValue(it.key).toString())
.value(elementValueAdapter.toJson(it.value))
I am still unsure about the reasoning behind it though. Thanks!

Related

Kotlin Generic problem, UNCHECKED_CAST , required:Nothing

#file:Suppress("UNCHECKED_CAST")
data class Element<T>(
val key: String,
val valueOne: T,
val valueTwo: T,
val comparator: Comparator<T>,
val comparatorValue: CompareResult
)
enum class CompareResult(
val value: Int
) {
LESS(-1),
EQUAL(0),
GREATER_THAN(1)
}
fun <T> matchesComparison(list:Collection<Element<T>>): Pair<Boolean, List<String>> {
val failedComparisons = mutableListOf<String>()
for (element in list) {
val compareValue = element.comparator.compare(element.valueOne, element.valueTwo)
if (element.comparatorValue.value != compareValue) {
failedComparisons.add(element.key)
}
}
return Pair(failedComparisons.isEmpty(), failedComparisons)
}
val stringComparator = Comparator.comparing(String::toString)
val intComparator = Comparator.comparing(Int::toInt)
val elementsToCompare = listOf(
Element("number", 1, 2, intComparator, CompareResult.LESS),
Element("first name", "a", "a", stringComparator, CompareResult.EQUAL),
Element("last name", "a", "b", stringComparator, CompareResult.EQUAL)
)
matchesComparison(elementsToCompare).second.joinToString(", ","Failed elements: \"","\"")
I often get faced with comparing two different object properties with the same values.
As an example object A has props number,firstname,lastname. What i want to do is create a list have and have a function which goes over these Elements and returns which props have failed the comparison. I've managed to use generics for both the object and the matchesComparison function which returns the failed comparisons. The problem begins when i want to pass this list which is of type Collection<Element<out Any>> to this function is i get a type missmatch. instead of using unchecked casts to force the Comparator to be of type Any i would like to do this
val stringComparator = Comparator.comparing(String::toString)
val intComparator = Comparator.comparing(Int::toInt)
The result value that of the script above should be Failed elements: "last name"
I tried changing the signature of the function to out any but then the comparator.compare method has both params as of type Nothing. I really want to avoid unsing unchecked casts.
matchesComparison() doesn't need to be generic in this case. It doesn't really care what is the type of the whole input collection, so we can simply use * here.
Then we have another problem. The compiler isn't smart enough to notice that while we perform operations on a single element, all its properties are of matching types. As a result, it doesn't allow to use element.comparator on element.valueOne and element.valueTwo. To fix this problem, we simply need to create a separate function which works on a single Element, so it understand the type for all properties is the same:
fun matchesComparison(list:Collection<Element<*>>): Pair<Boolean, List<String>> {
fun <T> Element<T>.matches() = comparatorValue.value == comparator.compare(valueOne, valueTwo)
val failedComparisons = mutableListOf<String>()
for (element in list) {
if (!element.matches()) {
failedComparisons.add(element.key)
}
}
return Pair(failedComparisons.isEmpty(), failedComparisons)
}
Also, I believe such matches() function should be actually a member function of Element. It seems strange that while Element is pretty independent and it contains everything that is needed to perform a comparison, it still requires to use external code for this. If it would have a matches() function then we wouldn't need to care about its T. matches() would work with any Element.

How to add data to Map copying existing values based on List of identifiers

Sorry for the poor title but it is rather hard to describe my use case in a short sentence.
Context
I have the following model:
typealias Identifier = String
data class Data(val identifier: Identifier,
val data1: String,
val data2: String)
And I have three main data structures in my use case:
A Set of Identifiers that exist and are valid in a given context. Example:
val existentIdentifiers = setOf("A-1", "A-2", "B-1", "B-2", "C-1")
A Map that contains a List of Data objects per Identifier. Example:
val dataPerIdentifier: Map<Identifier, List<Data>> = mapOf(
"A-1" to listOf(Data("A-1", "Data-1-A", "Data-2-A"), Data("A-1", "Data-1-A", "Data-2-A")),
"B-1" to listOf(Data("B-1", "Data-1-B", "Data-2-B")),
"C-1" to listOf(Data("C-1", "Data-1-C", "Data-2-C"))
)
A List of Lists that group together the Identifiers that should share the same List<Data> (each List includes always 2 Identifiers). Example
val identifiersWithSameData = listOf(listOf("A-1", "A-2"), listOf("B-1", "B-2"))
Problem / Use Case
The problem that I am trying to tackle stems from the fact that dataPerIdentifier might not contain all identifiersWithSameData given that existentIdentifiers contains such missing Identifiers. I need to add those missing Identifier to dataPerIdentifier, copying the List<Data> already in there.
Example
Given the data in the Context section:
A-1=[Data(identifier=A-1, data1=Data-1-A, data2=Data-2-A),
Data(identifier=A-1, data1=Data-1-A, data2=Data-2-A)],
B-1=[Data(identifier=B-1, data1=Data-1-B, data2=Data-2-B)],
C-1=[Data(identifier=C-1, data1=Data-1-C, data2=Data-2-C)]
The desired outcome is to update dataPerIdentifier so that it includes:
A-1=[Data(identifier=A-1, data1=Data-1-A, data2=Data-2-A),
Data(identifier=A-1, data1=Data-1-A, data2=Data-2-A)],
B-1=[Data(identifier=B-1, data1=Data-1-B, data2=Data-2-B)],
C-1=[Data(identifier=C-1, data1=Data-1-C, data2=Data-2-C)],
A-2=[Data(identifier=A-2, data1=Data-1-A, data2=Data-2-A),
Data(identifier=A-2, data1=Data-1-A, data2=Data-2-A)]
The reason is that existentIdentifiers contains A-2 that is missing in the initial dataPerIdentifier Map. B-2 is also missing in the initial dataPerIdentifier Map but existentIdentifiers does not contain it, so it is ignored.
Possible solution
I have already a working code (handleDataForMultipleIdentifiers() method is the one doing the heavy lifting), but it does not feel to be the cleanest or easiest to read:
fun main(args: Array<String>) {
val existentIdentifiers = setOf("A-1", "A-2", "B-1", "C-1")
val dataPerIdentifier: Map<Identifier, List<Data>> = mapOf(
"A-1" to listOf(Data("A-1", "Data-1-A", "Data-2-A"), Data("A-1", "Data-1-A", "Data-2-A")),
"B-1" to listOf(Data("B-1", "Data-1-B", "Data-2-B")),
"C-1" to listOf(Data("C-1", "Data-1-C", "Data-2-C"))
)
val identifiersWithSameData = listOf(listOf("A-1", "A-2"), listOf("B-1", "B-2"))
print("Original Data")
println(dataPerIdentifier)
print("Target Data")
println(dataPerIdentifier.handleDataForMultipleIdentifiers(identifiersWithSameData, existentIdentifiers))
}
fun Map<Identifier, List<Data>>.handleDataForMultipleIdentifiers(identifiersWithSameData: List<List<Identifier>>, existentIdentifiers: Set<Identifier>)
: Map<Identifier, List<Data>> {
val additionalDataPerIdentifier = identifiersWithSameData
.mapNotNull { identifiersList ->
val identifiersWithData = identifiersList.find { it in this.keys }
identifiersWithData?.let { it to identifiersList.minus(it).filter { it in existentIdentifiers } }
}.flatMap { (existentIdentifier, additionalIdentifiers) ->
val existentIdentifierData = this[existentIdentifier].orEmpty()
additionalIdentifiers.associateWith { identifier -> existentIdentifierData.map { it.copy(identifier = identifier) } }.entries
}.associate { it.key to it.value }
return this + additionalDataPerIdentifier
}
typealias Identifier = String
data class Data(val identifier: Identifier,
val data1: String,
val data2: String)
So my question is: how can I do this in a simpler way?
If identifiersWithSameData always contains 2 identifiers per item then it should not really be a list of lists, but rather a list of pairs or dedicated data classes. And if you convert this data structure into a map like this:
val identifiersWithSameData = mapOf("A-1" to "A-2", "A-2" to "A-1", "B-1" to "B-2", "B-2" to "B-1")
The the whole solution is pretty simple:
existentIdentifiers.associateWith {
dataPerIdentifier[it] ?: dataPerIdentifier[identifiersWithSameData[it]!!]!!
}
I'm not sure about both !!, for example I don't know if it is guaranteed that identifier existing in existentIdentifiers exists in identifiersWithSameData as well. You may need to tune this solution a little.

About binarySearch() of Kotlin List

I ran the examples in the official Kotlin documentation in the local Android Studio, and found that the results are different from what I expected, but I don’t know what is causing this?
data class Produce(
val name: String,
val price: Double
)
This is the data class I defined
val list2 = listOf(
Produce("AppCode", 52.0),
Produce("IDEA", 182.0),
Produce("VSCode", 2.75),
Produce("Eclipse", 1.75)
)
this is my source list
println(list2.sortedWith(compareBy<Produce> {
it.price
}.thenBy {
it.name
}))
The output on the console is:
[Produce(name=Eclipse, price=1.75), Produce(name=VSCode, price=2.75), Produce(name=AppCode, price=52.0), Produce(name=IDEA, price=182.0)]
I call binarySearch() like this
println("result: ${
list2.binarySearch(
Produce("AppCode", 52.0), compareBy<Produce> {
it.price
}.thenBy {
it.name
}
)
}")
I think the result should be 2, but it is 0
result: 0
I don't know why it turned out like this. Plase help me . thanks a lot
sortedWith() does not modify the list, it returns a new, sorted collection. When calling list2.binarySearch() you still search through original, unsorted list.
You need to either do something like:
list2.sortedWith().binarySearch()
Or create your list with mutableListOf() and then use sort() which sorts in-place.
Broot is right. You need to pass the sorted list to the binarySearch() function. To clarify in code:
val comparator = compareBy<Produce> { it.price }.thenBy { it.name }
val sorted = list2.sortedWith(comparator)
println(sorted.joinToString("\n"))
val foundIndex = sorted.binarySearch(Produce("AppCode", 52.0), comparator)
println("Found at: $foundIndex")
Result:
Produce(name=Eclipse, price=1.75)
Produce(name=VSCode, price=2.75)
Produce(name=AppCode, price=52.0)
Produce(name=IDEA, price=182.0)
Found at: 2

Why filtering out null map keys doesn't change type to not nullable in kotlin?

I have a list of objects with an optional id as String and I want to make a map out of it.
I want to have the keys of my map as non nullable: so something like this:
data class Foo(
val id: String? = null
val someStuff: String? = null,
)
val foo = listOf(Foo("id1"), Foo())
val bar = foo.filterNot { it.id == null }.associateBy { it.id }
Here bar type is Map<String?, Foo> but not Map<String, Foo>
My workaround is to add a non null asserted call: !!, but it doesn't seem clean.
Is there an easy and safe way to do this?
This looks like something that contracts could help with, but currently a contract expression can't access properties of the class in use.
As a workaround, you could define a 2nd class that has a non-null id, like so
data class Foo(
val id: String? = null,
val someStuff: String? = null
)
data class Foo2(
val id: String,
val someStuff: String? = null
)
val foo = listOf(Foo("id1"), Foo())
val bar = foo
.mapNotNull { if (it.id != null) Foo2(it.id, it.someStuff) else null }
.associateBy { it.id }
There's a six-year-old open feature request for Map.filterNotNullKeys() and a four-year old open feature request for Map.associateByNotNull().
In my opinion, the associateBy { it.id!! } would be cleanest for readability. But you could do it like this:
val bar = foo.mapNotNull { it.id?.run { it.id to it } }.toMap()
As for your actual question, that logic is way too many steps for the compiler to infer. Your last function call to associateBy sees a nullable, so it infers a nullable. For the compiler to figure this out, it would have to step back and see that the List that you call associateBy on happens to have filtered out certain objects in a way that happens to ensure that a certain nullable property won't be null within this specific list, and it's the same property that you are associating with. Now imagine it has to do this for every call to any generic function, and the various lambdas involved could potentially have multiple lines of code. Compile times would skyrocket.

How to deserialize dates with offset ("2019-01-29+01:00") to `java.time` related classes?

I've refactored some legacy code within Spring Boot (2.1.2) system and migrated from java.util.Date to java.time based classes (jsr310). The system expects the dates in a ISO8601 formated string, whereas some are complete timestamps with time information (e.g. "2019-01-29T15:29:34+01:00") while others are only dates with offset (e.g. "2019-01-29+01:00"). Here is the DTO (as Kotlin data class):
data class Dto(
// ...
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ssXXX")
#JsonProperty("processingTimestamp")
val processingTimestamp: OffsetDateTime,
// ...
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-ddXXX")
#JsonProperty("orderDate")
val orderDate: OffsetDateTime,
// ...
)
While Jackson perfectly deserializes processingTimestamp, it fails with orderDate:
Caused by: java.time.DateTimeException: Unable to obtain OffsetDateTime from TemporalAccessor: {OffsetSeconds=32400},ISO resolved to 2018-10-23 of type java.time.format.Parsed
at java.time.OffsetDateTime.from(OffsetDateTime.java:370) ~[na:1.8.0_152]
at com.fasterxml.jackson.datatype.jsr310.deser.InstantDeserializer.deserialize(InstantDeserializer.java:207) ~[jackson-datatype-jsr310-2.9.8.jar:2.9.8]
This makes sense to me, since OffsetDateTime cannot find any time information necessary to construct the instant. If I change to val orderDate: LocalDate Jackson can successfully deserialize, but then the offset information is gone (which I need to convert to Instant later).
Question
My current workaround is to use OffsetDateTime, in combination with a custom deserializer (see below). But I'm wondering, if there is a better solution for this?
Also, I'd wish for a more appropriate data type like OffsetDate, but I cannot find it in java.time.
PS
I was asking myself if "2019-01-29+01:00" is a valid for ISO8601. However, since I found that java.time.DateTimeFormatter.ISO_DATE is can correctly parse it and I cannot change the format how the clients send data, I put aside this question.
Workaround
data class Dto(
// ...
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-ddXXX")
#JsonProperty("catchDate")
#JsonDeserialize(using = OffsetDateDeserializer::class)
val orderDate: OffsetDateTime,
// ...
)
class OffsetDateDeserializer(
private val formatter: DateTimeFormatter = DateTimeFormatter.ISO_DATE
) : JSR310DateTimeDeserializerBase<OffsetDateTime>(OffsetDateTime::class.java, formatter) {
override fun deserialize(parser: JsonParser, context: DeserializationContext): OffsetDateTime? {
if (parser.hasToken(JsonToken.VALUE_STRING)) {
val string = parser.text.trim()
if (string.isEmpty()) {
return null
}
val parsed: TemporalAccessor = formatter.parse(string)
val offset = if(parsed.isSupported(ChronoField.OFFSET_SECONDS)) ZoneOffset.from(parsed) else ZoneOffset.UTC
val localDate = LocalDate.from(parsed)
return OffsetDateTime.of(localDate.atStartOfDay(), offset)
}
throw context.wrongTokenException(parser, _valueClass, parser.currentToken, "date with offset must be contained in string")
}
override fun withDateFormat(otherFormatter: DateTimeFormatter?): JsonDeserializer<OffsetDateTime> = OffsetDateDeserializer(formatter)
}
As #JodaStephen explained in the comments, OffsetDate was not included in java.time to have a minimal set of classes. So, OffsetDateTime is the best option.
He also suggested to use DateTimeFormatterBuilder and parseDefaulting to create a DateTimeFormatter instance, to directly create OffsetDateTime from the formatters parsing result (TemporalAccessor). AFAIK, I still need to create a custom deserializer to use the formatter. Here is code, which solved my problem:
class OffsetDateDeserializer: JsonDeserializer<OffsetDateTime>() {
private val formatter = DateTimeFormatterBuilder()
.append(DateTimeFormatter.ISO_DATE)
.parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
.parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
.parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
.parseDefaulting(ChronoField.MILLI_OF_SECOND, 0)
.parseDefaulting(ChronoField.OFFSET_SECONDS, 0)
.toFormatter()
override fun deserialize(parser: JsonParser, context: DeserializationContext): OffsetDateTime? {
if (parser.hasToken(JsonToken.VALUE_STRING)) {
val string = parser.text.trim()
if (string.isEmpty()) {
return null
}
try {
return OffsetDateTime.from(formatter.parse(string))
} catch (e: DateTimeException){
throw context.wrongTokenException(parser, OffsetDateTime::class.java, parser.currentToken, "error while parsing date: ${e.message}")
}
}
throw context.wrongTokenException(parser, OffsetDateTime::class.java, parser.currentToken, "date with offset must be contained in string")
}
}