Is there a way to register a codec for multiple classes? Basically, all my classes should just be serialized using a Jackson object mapper. But it seems like I have to create a custom codec for each class (even though I can abstract it a little bit using generics).
A small code example:
Codec:
class JacksonCodec<T>(private val mapper: ObjectMapper, private val clazz: Class<T>) : MessageCodec<T, T> {
override fun encodeToWire(buffer: Buffer, s: T) {
buffer.appendBytes(mapper.writeValueAsBytes(s))
}
override fun decodeFromWire(pos: Int, buffer: Buffer): T {
val length = buffer.getInt(pos)
val bytes = buffer.getBytes(pos + 4, pos + 4 + length)
return mapper.readValue(bytes, clazz)
}
...
}
register codec for each class I want to serialize:
vertx.eventBus()
.registerDefaultCodec(A::class.java, JacksonCodec(DatabindCodec.mapper(), A::class.java))
vertx.eventBus()
vertx.eventBus()
.registerDefaultCodec(B::class.java, JacksonCodec(DatabindCodec.mapper(), B::class.java))
vertx.eventBus()
The code examples are kotlin but same applies for Java.
As far as I can tell looking at the code, there is no way, as the class needs to be the exact match:
https://github.com/eclipse-vertx/vert.x/blob/master/src/main/java/io/vertx/core/eventbus/impl/CodecManager.java#L99
It is possible, with some limitations and quirks. I would not recommend doing it.
Let's start with the limitations:
It can not be used in clustered mode
You have to declare the codec name every time you send something over the eventbus.
If you create a generic codec that encodes classes with Jackson and every time you send something over the eventbus you make sure to add it using codecName in the deliveryOptions, you can register it only once and use it for all of your classes.
Full example:
fun main() {
val vertx = Vertx.vertx()
vertx.eventBus().registerCodec(GenericCodec())
vertx.eventBus().consumer<Foo>("test-address") {
println(it.body())
it.reply(Bar(), genericDeliveryOptions)
}
vertx.eventBus().request<String>("test-address", Foo(), genericDeliveryOptions) {
println(it.result().body())
}
vertx.close()
}
data class Foo(
val foo: String = "foo",
)
data class Bar(
val bar: String = "bar",
)
class GenericCodec : MessageCodec<Any, Any> {
companion object {
const val NAME = "generic"
}
private val mapper: ObjectMapper = ObjectMapper()
override fun encodeToWire(buffer: Buffer, s: Any) {
buffer.appendBytes(mapper.writeValueAsBytes(s))
}
override fun decodeFromWire(pos: Int, buffer: Buffer): Any {
throw RuntimeException("should never get here, unless using clustered mode")
}
override fun transform(s: Any): Any {
return s
}
override fun name(): String {
return NAME
}
override fun systemCodecID(): Byte {
return -1
}
}
val genericDeliveryOptions = deliveryOptionsOf(codecName = GenericCodec.NAME)
I would like to do mapping of nested object that needs value from the parent object. I could use solution mentioned here mapstruct - Propagate parent field value to collection of nested objects - either directly after mapping to set some value to the child object or to use context. But in my case I work with immutable objects.
example:
data class Worker(
val name: String,
val businessCard: BusinessCard? = null,
)
data class BusinessCard(
val companyName: String,
)
data class WorkerDto(
val name: String,
val businessCard: BusinessCardDto? = null,
)
data class BusinessCardDto(
val text: String, // "worker name | company name"
)
Is there a way how to directly map value without #AfterMapping modifications?
Something like this?
#Mapper(config = CustomMappingConfig::class, uses = [ComputerMapper::class])
abstract class WorkerMapper {
#Mapping(target = "businessCard.text", expression = "java(mapBcText(worker))")
abstract fun mapWorker(worker: Worker): WorkerDto
protected fun mapBcText(worker: Worker) = "${worker.name} | ${worker.businessCard?.companyName}"
}
But sadly the code above generates:
#Override
public WorkerDto mapWorker(Worker worker) {
if ( worker == null ) {
return null;
}
String name = null;
BusinessCardDto businessCard = null;
name = worker.getName();
businessCard = businessCardToBusinessCardDto( worker.getBusinessCard() );
WorkerDto workerDto = new WorkerDto( name, businessCard );
return workerDto;
}
protected BusinessCardDto businessCardToBusinessCardDto(BusinessCard businessCard) {
if ( businessCard == null ) {
return null;
}
BusinessCardDto businessCardDto = new BusinessCardDto();
businessCardDto.setText( mapBcText(worker) ); // WORKER IS NOT ACCESSIBLE HERE
return businessCardDto;
}
Does anybody have an idea how to achieve this mapping?
...I also tried to create custom BusinessCard mapper, but then I cannot access the parent data (Worker) in it then...
you need to use var instead of val in your dataclass.
mapstruct don't seem to manage immutable kotlin class for the moment.
I declared a data class in a Kotlin function, but the data is empty after gson conversion.
fun writeAndFlush(context: StateMachine) {
data class Temp(val model: TaskModel, val totalTime: String?, val state: String)
val temp = Temp(context.businessObj, context.totalTime, context.state.toString())
Log.e("test", temp.toString()) // print data here.
val json = Gson().toJson(temp)
Log.e("test", json) // problem here.....print null
}
Is there any problem with this way?
I hava a class Packet.java(can't modify) in a package.
public class Packet implements java.io.Serializable, Cloneable {
private static final AtomicLong ID_ATOMICLONG = new AtomicLong();
private Long id = ID_ATOMICLONG.incrementAndGet();
}
I use own class LoginPacket.kt (can modify)
class LoginPacket : Packet () {
var id = "" ( this name must be id )
fun parsePacket(input: String): Boolean {
val map = HashMap<String,Any>()
map["id"] = "5d6ff3433354b4d43076419"
var wrapper: BeanWrapper = PropertyAccessorFactory.forBeanPropertyAccess(this)
wrapper.isAutoGrowNestedPaths = true
// question is here , I can not set id as String use BeanWrapper, Only can set id as Long
// and also I can replace id's getter and setter method
val pd = wrapper.getPropertyDescriptor("id")
pd.readMethod = LoginPacket::id.getter.javaMethod
pd.writeMethod = LoginPacket::id.setter.javaMethod
wrapper.setPropertyValues(map)
}
}
So what I can do next?
Thanks very much for sharing!
Beanwrapper link
It is not possible to override the type of a field.
What you can do instead depends on what you are trying to do, and which libraries you are using.
I can think of one way that may work, assuming your library does not need an instance nor subclass of Packet.
And that is creating your own class that only implements the interfaces:
class LoginPacket(): java.io.Serializable, Cloneable {
// You may or may not need this.
// Since the original version uses it to generate the ID,
// I think you can skip this part.
companion object {
#JvmStatic
private val ID_ATOMICLONG = AtomicLong()
}
var id : String = ""
fun parsePacket(input: String): Boolean {
val map = HashMap<String,Any>()
map["id"] = "5d6ff3433354b4d43076419"
var wrapper: BeanWrapper = PropertyAccessorFactory.forBeanPropertyAccess(this)
wrapper.isAutoGrowNestedPaths = true
val pd = wrapper.getPropertyDescriptor("id")
pd.readMethod = LoginPacket::id.getter.javaMethod
pd.writeMethod = LoginPacket::id.setter.javaMethod
wrapper.setPropertyValues(map)
}
}
It is hard to provide better answers without more context.
Although similar to Convert DBObject to a POJO using MongoDB Java Driver my question is different in that I am specifically interested in using Jackson for mapping.
I have an object which I want to convert to a Mongo DBObject instance. I want to use the Jackson JSON framework to do the job.
One way to do so is:
DBObject dbo = (DBObject)JSON.parse(m_objectMapper.writeValueAsString(entity));
However, according to https://github.com/FasterXML/jackson-docs/wiki/Presentation:-Jackson-Performance this is the worst way to go. So, I am looking for an alternative. Ideally, I would like to be able to hook into the JSON generation pipeline and populate a DBObject instance on the fly. This is possible, because the target in my case is a BasicDBObject instance, which implements the Map interface. So, it should fit into the pipeline easily.
Now, I know I can convert an object to Map using the ObjectMapper.convertValue function and then recursively convert the map to a BasicDBObject instance using the map constructor of the BasicDBObject type. But, I want to know if I can eliminate the intermediate map and create the BasicDBObject directly.
Note, that because a BasicDBObject is essentially a map, the opposite conversion, namely from a scalar DBObject to a POJO is trivial and should be quite efficient:
DBObject dbo = getDBO();
Class clazz = getObjectClass();
Object pojo = m_objectMapper.convertValue(dbo, clazz);
Lastly, my POJO do not have any JSON annotations and I would like it to keep this way.
You can probably use Mixin annotations to annotate your POJO and the BasicDBObject (or DBObject), so annotations is not a problem. Since BasicDBOject is a map, you can use #JsonAnySetter on the put method.
m_objectMapper.addMixInAnnotations(YourMixIn.class, BasicDBObject.class);
public interface YourMixIn.class {
#JsonAnySetter
void put(String key, Object value);
}
This is all I can come up with since I have zero experience with MongoDB Object.
Update: MixIn are basically a Jackson mechanism to add annotation to a class without modifying said class. This is a perfect fit when you don't have control over the class you want to marshal (like when it's from an external jar) or when you don't want to clutter your classes with annotation.
In your case here, you said that BasicDBObject implements the Map interface, so that class has the method put, as defined by the map interface. By adding #JsonAnySetter to that method, you tell Jackson that whenever he finds a property that he doesn't know after introspection of the class to use the method to insert the property to the object. The key is the name of the property and the value is, well, the value of the property.
All this combined makes the intermediate map go away, since Jackson will directly convert to the BasicDBOject because it now knows how to deserialize that class from Json. With that configuration, you can do:
DBObject dbo = m_objectMapper.convertValue(pojo, BasicDBObject.class);
Note that I haven't tested this because I don't work with MongoDB, so there might be some loose ends. However, I have used the same mechanism for similar use cases without any problem. YMMV depending on the classes.
Here's an example of a simple serializer (written in Scala) from POJO to BsonDocument which could be used with version 3 of Mongo driver. The de-serializer would be somewhat more difficult to write.
Create a BsonObjectGenerator object which would do a streaming serialization to Mongo Bson directly:
val generator = new BsonObjectGenerator
mapper.writeValue(generator, POJO)
generator.result()
Here's the code for a serializer:
class BsonObjectGenerator extends JsonGenerator {
sealed trait MongoJsonStreamContext extends JsonStreamContext
case class MongoRoot(root: BsonDocument = BsonDocument()) extends MongoJsonStreamContext {
_type = JsonStreamContext.TYPE_ROOT
override def getCurrentName: String = null
override def getParent: MongoJsonStreamContext = null
}
case class MongoArray(parent: MongoJsonStreamContext, arr: BsonArray = BsonArray()) extends MongoJsonStreamContext {
_type = JsonStreamContext.TYPE_ARRAY
override def getCurrentName: String = null
override def getParent: MongoJsonStreamContext = parent
}
case class MongoObject(name: String, parent: MongoJsonStreamContext, obj: BsonDocument = BsonDocument()) extends MongoJsonStreamContext {
_type = JsonStreamContext.TYPE_OBJECT
override def getCurrentName: String = name
override def getParent: MongoJsonStreamContext = parent
}
private val root = MongoRoot()
private var node: MongoJsonStreamContext = root
private var fieldName: String = _
def result(): BsonDocument = root.root
private def unsupported(): Nothing = throw new UnsupportedOperationException
override def disable(f: Feature): JsonGenerator = this
override def writeStartArray(): Unit = {
val array = new BsonArray
node match {
case MongoRoot(o) =>
o.append(fieldName, array)
fieldName = null
case MongoArray(_, a) =>
a.add(array)
case MongoObject(_, _, o) =>
o.append(fieldName, array)
fieldName = null
}
node = MongoArray(node, array)
}
private def writeBsonValue(value: BsonValue): Unit = node match {
case MongoRoot(o) =>
o.append(fieldName, value)
fieldName = null
case MongoArray(_, a) =>
a.add(value)
case MongoObject(_, _, o) =>
o.append(fieldName, value)
fieldName = null
}
private def writeBsonString(text: String): Unit = {
writeBsonValue(BsonString(text))
}
override def writeString(text: String): Unit = writeBsonString(text)
override def writeString(text: Array[Char], offset: Int, len: Int): Unit = writeBsonString(new String(text, offset, len))
override def writeString(text: SerializableString): Unit = writeBsonString(text.getValue)
private def writeBsonFieldName(name: String): Unit = {
fieldName = name
}
override def writeFieldName(name: String): Unit = writeBsonFieldName(name)
override def writeFieldName(name: SerializableString): Unit = writeBsonFieldName(name.getValue)
override def setCodec(oc: ObjectCodec): JsonGenerator = this
override def useDefaultPrettyPrinter(): JsonGenerator = this
override def getFeatureMask: Int = 0
private def writeBsonBinary(data: Array[Byte]): Unit = {
writeBsonValue(BsonBinary(data))
}
override def writeBinary(bv: Base64Variant, data: Array[Byte], offset: Int, len: Int): Unit = {
val res = if (offset != 0 || len != data.length) {
val subset = new Array[Byte](len)
System.arraycopy(data, offset, subset, 0, len)
subset
} else {
data
}
writeBsonBinary(res)
}
override def writeBinary(bv: Base64Variant, data: InputStream, dataLength: Int): Int = unsupported()
override def isEnabled(f: Feature): Boolean = false
override def writeRawUTF8String(text: Array[Byte], offset: Int, length: Int): Unit = writeBsonString(new String(text, offset, length, "UTF-8"))
override def writeRaw(text: String): Unit = unsupported()
override def writeRaw(text: String, offset: Int, len: Int): Unit = unsupported()
override def writeRaw(text: Array[Char], offset: Int, len: Int): Unit = unsupported()
override def writeRaw(c: Char): Unit = unsupported()
override def flush(): Unit = ()
override def writeRawValue(text: String): Unit = writeBsonString(text)
override def writeRawValue(text: String, offset: Int, len: Int): Unit = writeBsonString(text.substring(offset, offset + len))
override def writeRawValue(text: Array[Char], offset: Int, len: Int): Unit = writeBsonString(new String(text, offset, len))
override def writeBoolean(state: Boolean): Unit = {
writeBsonValue(BsonBoolean(state))
}
override def writeStartObject(): Unit = {
node = node match {
case p#MongoRoot(o) =>
MongoObject(null, p, o)
case p#MongoArray(_, a) =>
val doc = new BsonDocument
a.add(doc)
MongoObject(null, p, doc)
case p#MongoObject(_, _, o) =>
val doc = new BsonDocument
val f = fieldName
o.append(f, doc)
fieldName = null
MongoObject(f, p, doc)
}
}
override def writeObject(pojo: scala.Any): Unit = unsupported()
override def enable(f: Feature): JsonGenerator = this
override def writeEndArray(): Unit = {
node = node match {
case MongoRoot(_) => unsupported()
case MongoArray(p, a) => p
case MongoObject(_, _, _) => unsupported()
}
}
override def writeUTF8String(text: Array[Byte], offset: Int, length: Int): Unit = writeBsonString(new String(text, offset, length, "UTF-8"))
override def close(): Unit = ()
override def writeTree(rootNode: TreeNode): Unit = unsupported()
override def setFeatureMask(values: Int): JsonGenerator = this
override def isClosed: Boolean = unsupported()
override def writeNull(): Unit = {
writeBsonValue(BsonNull())
}
override def writeNumber(v: Int): Unit = {
writeBsonValue(BsonInt32(v))
}
override def writeNumber(v: Long): Unit = {
writeBsonValue(BsonInt64(v))
}
override def writeNumber(v: BigInteger): Unit = unsupported()
override def writeNumber(v: Double): Unit = {
writeBsonValue(BsonDouble(v))
}
override def writeNumber(v: Float): Unit = {
writeBsonValue(BsonDouble(v))
}
override def writeNumber(v: BigDecimal): Unit = unsupported()
override def writeNumber(encodedValue: String): Unit = unsupported()
override def version(): Version = unsupported()
override def getCodec: ObjectCodec = unsupported()
override def getOutputContext: JsonStreamContext = node
override def writeEndObject(): Unit = {
node = node match {
case p#MongoRoot(_) => p
case MongoArray(p, a) => unsupported()
case MongoObject(_, p, _) => p
}
}
}
You might be intereted in checking how jongo does it. It is open source and the code can be found on github. Or you could also simply use their library. I use a mix of jongo and plain DBObjects when I need more flexibility.
They claim that they are (almost) as fast as using the Java driver directly so I suppose their method is efficient.
I use the little helper utility class below which is inspired from their code base and uses a mix of Jongo (the MongoBsonFactory) and Jackson to convert between DBObjects and POJOs. Note that the getDbObject method does a deep copy of the DBObject to make it editable - if you don't need to customise anything you can remove that part and improve performance.
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectReader;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.fasterxml.jackson.databind.introspect.VisibilityChecker;
import com.mongodb.BasicDBObject;
import com.mongodb.DBEncoder;
import com.mongodb.DBObject;
import com.mongodb.DefaultDBEncoder;
import com.mongodb.LazyWriteableDBObject;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import org.bson.LazyBSONCallback;
import org.bson.io.BasicOutputBuffer;
import org.bson.io.OutputBuffer;
import org.jongo.marshall.jackson.bson4jackson.MongoBsonFactory;
public class JongoUtils {
private final static ObjectMapper mapper = new ObjectMapper(MongoBsonFactory.createFactory());
static {
mapper.setVisibilityChecker(VisibilityChecker.Std.defaultInstance().withFieldVisibility(
JsonAutoDetect.Visibility.ANY));
}
public static DBObject getDbObject(Object o) throws IOException {
ObjectWriter writer = mapper.writer();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
writer.writeValue(baos, o);
DBObject dbo = new LazyWriteableDBObject(baos.toByteArray(), new LazyBSONCallback());
//turn it into a proper DBObject otherwise it can't be edited.
DBObject result = new BasicDBObject();
result.putAll(dbo);
return result;
}
public static <T> T getPojo(DBObject o, Class<T> clazz) throws IOException {
ObjectReader reader = mapper.reader(clazz);
DBEncoder dbEncoder = DefaultDBEncoder.FACTORY.create();
OutputBuffer buffer = new BasicOutputBuffer();
dbEncoder.writeObject(buffer, o);
T pojo = reader.readValue(buffer.toByteArray());
return pojo;
}
}
Sample usage:
Pojo pojo = new Pojo(...);
DBObject o = JongoUtils.getDbObject(pojo);
//you can customise it if you want:
o.put("_id", pojo.getId());
I understand that this is a very old question, but if asked today I would instead recommend the built-in POJO support on the official Mongo Java driver.
Here's an update to assylias' answer that doesn't require Jongo and is compatible with the Mongo 3.x drivers. It also handles nested object graphs, I couldn't get that to work with LazyWritableDBObject which has been removed in the mongo 3.x drivers anyway.
The idea is to tell Jackson how to serialize an object to a BSON byte array, and then deserialize the BSON byte array into BasicDBObject. I'm sure you can find some low level API in the mongo-java-drivers if you want to ship the BSON bytes directly to the database. You will need a dependency to bson4jackson in order for ObjectMapper to serialize BSON when you call writeValues(ByteArrayOutputStream, Object):
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;
import de.undercouch.bson4jackson.BsonFactory;
import de.undercouch.bson4jackson.BsonParser;
import org.bson.BSON;
import org.bson.BSONObject;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
public class MongoUtils {
private static ObjectMapper mapper;
static {
BsonFactory bsonFactory = new BsonFactory();
bsonFactory.enable(BsonParser.Feature.HONOR_DOCUMENT_LENGTH);
mapper = new ObjectMapper(bsonFactory);
}
public static DBObject getDbObject(Object o) {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
mapper.writeValue(baos, o);
BSONObject decode = BSON.decode(baos.toByteArray());
return new BasicDBObject(decode.toMap());
} catch (IOException e) {
throw new RuntimeException(e);
}
}
}