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@mikehearn
Created December 17, 2015 10:53
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A Kryo serialiser that lets you serialise immutable classes like "class Foo(val a: Int, val b: Bar)" without bypassing the c'tor.
interface SerializeableWithKryo
class ImmutableClassSerializer<T : SerializeableWithKryo>(val klass: KClass<T>) : Serializer<T>() {
val props = klass.memberProperties.sortedBy { it.name }
val propsByName = props.toMapBy { it.name }
val constructor = klass.primaryConstructor!!
init {
// Verify that this class is immutable (all properties are final)
assert(props.none { it is KMutableProperty<*> })
}
override fun write(kryo: Kryo, output: Output, obj: T) {
output.writeVarInt(constructor.parameters.size, true)
output.writeInt(constructor.parameters.hashCode())
for (param in constructor.parameters) {
val kProperty = propsByName[param.name!!]!!
when (param.type.javaType.typeName) {
"int" -> output.writeVarInt(kProperty.get(obj) as Int, true)
"long" -> output.writeVarLong(kProperty.get(obj) as Long, true)
"short" -> output.writeShort(kProperty.get(obj) as Int)
"char" -> output.writeChar(kProperty.get(obj) as Char)
"byte" -> output.writeByte(kProperty.get(obj) as Byte)
"double" -> output.writeDouble(kProperty.get(obj) as Double)
"float" -> output.writeFloat(kProperty.get(obj) as Float)
else -> try {
kryo.writeClassAndObject(output, kProperty.get(obj))
} catch (e: Exception) {
throw IllegalStateException("Failed to serialize ${param.name} in ${klass.qualifiedName}", e)
}
}
}
}
override fun read(kryo: Kryo, input: Input, type: Class<T>): T {
assert(type.kotlin == klass)
assert(kryo.isRegistrationRequired)
val numFields = input.readVarInt(true)
val fieldTypeHash = input.readInt()
// A few quick checks for data evolution. Note that this is not guaranteed to catch every problem! But it's
// good enough for a prototype.
if (numFields != constructor.parameters.size)
throw KryoException("Mismatch between number of constructor parameters and number of serialised fields for ${klass.qualifiedName} ($numFields vs ${constructor.parameters.size})")
if (fieldTypeHash != constructor.parameters.hashCode())
throw KryoException("Hashcode mismatch for parameter types for ${klass.qualifiedName}: unsupported type evolution has happened.")
val args = arrayOfNulls<Any?>(numFields)
var cursor = 0
for (param in constructor.parameters) {
args[cursor++] = when (param.type.javaType.typeName) {
"int" -> input.readVarInt(true)
"long" -> input.readVarLong(true)
"short" -> input.readShort()
"char" -> input.readChar()
"byte" -> input.readByte()
"double" -> input.readDouble()
"float" -> input.readFloat()
else -> kryo.readClassAndObject(input)
}
}
// If the constructor throws an exception, pass it through instead of wrapping it.
return try { constructor.call(*args) } catch (e: InvocationTargetException) { throw e.cause!! }
}
}
@wafisher
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wafisher commented Feb 4, 2017

Example usage?

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