An annotation processor that generates Moshi adapters from Kotlin classes.
There is a reflective adapter for Kotlin but that requires the kotlin reflection library which adds a lot of methods and increase the binary size which in a constrained environment such as Android is something is not preferable.
This is where Kotshi comes in, it generates fast and optimized adapters for your Kotlin data classes, just as if you'd hand written them yourself. It will automatically regenerate the adapters when you modify your class.
It's made to work with minimal setup, through there are limitations. Most of the limitations will be addressed as the support for Kotlin annotation processors improves.
First you must annotate your objects with the
@JsonSerializable data class Person( val name: String, val email: String?, val hasVerifiedAccount: Boolean, // This property has a different name in the Json than here so @Json must be applied. @Json(name = "created_at") val signUpDate: Date, // This field has a default value which will be used if the field is missing. val jobTitle: String? = null )
The following types are supported:
object(serialized as an empty JSON object)
Then create a class that will be your factory:
@KotshiJsonAdapterFactory object ApplicationJsonAdapterFactory : JsonAdapter.Factory by KotshiApplicationJsonAdapterFactory
Lastly just add the factory to your Moshi instance and you're all set:
val moshi = Moshi.Builder() .add(ApplicationJsonAdapterFactory.INSTANCE) .build()
By default adapters aren't requested for primitive types (even boxed primitive
types) since it is worse for performance and most people will not have custom
If you need to use custom adapters you can enable it per module be passing the
@KotshiJsonAdapterFactory or on a per adapter
by passing the same argument to
@JsonSerializable (the default is to follow
the module wide setting).
@JsonSerializableis the annotation used to generate
JsonAdapter's. Should only be placed on data classes, enums, sealed classes and objects.
@KotshiJsonAdapterFactorymakes Kotshi generate a JsonAdapter factory. Should be placed on an abstract class that implements
@JsonDefaultValuecan be used to annotated a fallback for enums or sealed classes when an unknown entry is encountered. The default is to thrown an exception.
You can use default values just like you normally would in Kotlin.
Due to limitations in Kotlin two instances of the object will be created when a class uses default values
(youtrack issue). This also means that composite default values are not
supported (for example a
fullName property that is
For enum entries and sealed classes you may annotate a single type with
@JsonDefaultValue to indicate that the entry
should be used when an unknown value is encountered (by default an exception is thrown).
Properties marked with
@Transient are not serialized. All transient properties must have a default value.
Only properties declared in the constructor needs to be annotated since other properties are ignores.
By default the property or enum entry name is used when reading and writing JSON. To change the name used you may use
@Json annotation from Moshi to annotate the property or enum entry.
Kotshi has full support for
@JsonQualifier, both plain and those with arguments. Simply annotate a property with the
desired qualifiers and Kotshi will pick them up.
- Kotshi only processes files written in Kotlin, types written in Java are not supported.
- Only data classes, enums, sealed classes and objects are supported.
- Only constructor properties will be serialized.
- Qualifiers whose arguments are named as a Java keyword cannot be seen by annotations processors and cannot be used.
- Due to limitation in KAPT, properties with a
javakeyword as a name cannot be marked as transient.
- Default values that depend on other constructor properties is not supported (youtrack issue).
- Due to a KAPT bug/limitation you cannot add qualifiers to parameters that are inline classes (youtrack issue).
implementation "se.ansman.kotshi:api:2.3.0" kapt "se.ansman.kotshi:compiler:2.3.0"
Snapshots of the development version are available in jfrogs's snapshots repository.
Copyright 2017-2020 Nicklas Ansman Giertz. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.