I need to provide a different version of response object for the same existing URI. I am going with Accept/Content-type conneg methodologies. I am using Jackson to covert my POJO into json. please help me how should i do it with jackson.
for the object model, must i have a base class and object versions are extended class?
Instead of having one object that would be serialized in two different ways, I'd recommend using two separate DTOs. One for each version.
The content negotiation will happen not on Jackson's side, but on the JAX-RS side with the #Produces annotation.
One method returning DTOv1 will produce application/vnd.v1+json while the other will return DTOv2 with application/vnd.v2+json.
Related
I can't find any explanation about difference between jackson's ObjectMapper to other mappers like dozer/mapStruct/modelMapping/etc. All the articles compare dozer/mapStruct/modelMapping but they ignore ObjectMapper. I can't understand what is wrong? Is the same mapper?
Dozer, MapStruct and ModelMapping are Java Bean to Java Bean mappers frameworks that recursively copies data from one object to another, property by property, field by field.
From other side, ObjectMapper provides functionality for reading and writing JSON, either to and from basic POJOs, or to and from a general-purpose JSON Tree Model. ObjectMapper has some additional features like converting objects (see convertValue method) but it is not a main reason why this class was created.
So, if you want to implement sophisticated mapping between two different models you should use mappers; if you want to serialise model to JSON or deserialise model from JSON payload you have to use ObjectMapper from Jackson.
Jackson library- Mainly concerned with converting Objects/ Entities to JSON and back.
ModelMapper/ MapStruct - Concerned with mapping One entity to another like, mapping an Entity to its DTO. This operation can get pretty gnarly owing to the size and complexity of different entities, so we need these libraries to make work easier.
I am trying to think of scenario to use Jackson TreeModel and Databinding API (Object mapper). When you would chose one again the another ?
URL-es you added to a question contain the answer in the overview.
Working with Tree Model
We’ll use JsonNode for various conversions as well as adding,
modifying and removing nodes.
and
Intro to the Jackson ObjectMapper
This write-up is focused on understanding the Jackson ObjectMapper
class – and how to serialize Java objects into JSON and deserialize
JSON string into Java objects.
I can only confirm that. 99% of examples I had to serialize Java POJO classes to JSON and vice versa. When I need to change a little JSON I use Tree Model to avoid whole serializing and deserializing process.
How can one obtain a default deserialized object in a custom Jackson deserializer?
I have an object which contains some fields which are not to be serialized, but which I wish to always be populated upon deserialization. In other words, a post-deserialize step.
I have created my own deserializer and annotated the class with a corresponding #JsonDeserialize, but I don't want to deserialize each field in the domain object by hand. Is there a way to get the regular deserialized object so I can just populate my custom fields? (Or else, just register a post-deserialization processor on a bean)
I have seen the answer to this question which hints at an answer, but I'm sufficiently unaware of the Jackson API to determine how best to actually effect this.
This can be achieved by using a BeanSerializerModifier and extending BeanSerializerBase, as per #ryanp's answer to this question.
My WCF client and server exchange objects whose types are defined on a class library shared by both, the server and the client. These objects implement custom serialization via ISerializable. However, my custom serialization is not being used. DataContractSerializer is being used, instead. How do I force my custom serialization to be used?
The reason why I need to use my own serialization is because I do trasfer some big object graphs and my serialization algorithm does a good job in compressing/speeding up things.
This is possible by adding the correct attributes to your wcf contact.
See: http://www.danrigsby.com/blog/index.php/2008/03/07/xmlserializer-vs-datacontractserializer-serialization-in-wcf/ for details.
If this does not help, show some code of how you have told the wcf contract that it should use the custom serializer.
how does Serialization of objects works? How object got deserialized and a instance is created from serialized date without a call to any constructor?
I've kept this answer language agnostic since a language wasn't given.
When the object is serialized, all the require information to rebuild it is encoded in way which can be retrieved. This typically includes the type of the object, as well as the value of all the instance variables.
When the object is deserialized, an area in memory of the correct size is allocated and is populated using the serialized information such that the new object is identical to the serialized one.
The running program can then refer to this new object in memory without having to actually call the constructor.
There are lots of little details which this doesn't explain, but this is the general idea of serialization/deserialization.
Are you talking about Java? If so, serialization is an extralingual object creation mechanism. It's a backdoor that uses native code to create the object without calling any constructors. Therefore, when designing a class for serializability, you need to make sure that a class created through deserialization maintains the same invariants (key fields being initialized) as you would through the constructor path. A third way to create objects in Java is through cloning, and similar issues apply.
Cloning and serialization don't interact well with the use of final fields if you need to set the value of that field to something different than what is returned by clone or the deserialization process.
Josh Bloch's "Effective Java" has some chapters that explain these issues in more depth.
(this answer may apply to other languages too, but I've only used serialization in Java)
Regarding .NET: this isn't a definitive or textbook answer, and I might be all-out wrong...
.NET Serialization needs to be seperated out into Binary vs. others (XML or an XML derivitave typically). Binary serialization is mostly a black-box to me, but it allows the object to be serialized and restored in their current state. XML serialization typically only serialized the public fields/properties of an object, unless overriden by adding a custom ISerializable implementation.
In the case of XML serialization I believe .NET uses Reflection to determine which fields and properties get converted to their equivalent Elements. Adding an [XMLSerializable] attribute will implement a default behavior which can be adjusted by applying other attributes at the field level (such as [XMLAttribute]).
The metadata (which Reflection depends on) stores all the object members as well as their attributes and addresses, which allows the serializer to determine how it should build the output.