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Supply Polymorphic De-serialization/Serialization parameters to REST endpoint without changing POJOs

I am working on a JAX-RS application, where endpoints Consume and Produce JSON type data. And I am using Jackson for that purpose.
As I know one of the ways to handle Polymorphic behavior in Jackson is to use #JsonTypeInfo and #JsonSubTypes on POJOs.
But in my case POJOs are not part of code, they're embedded in a JAR file and I can't edit them.
Is there any way where I can specify this info to Jackson externally without POJO annotations ?
Please point me to the right direction of this has already been discussed earlier.

Is there any way where I can specify this info to Jackson externally without POJO annotations?
Using annotations is still a valid approach if you consider mix-in annotations.
When modifying the source code is not an option, you can use mix-in annotations to add Jackson annotations to a bean. You can think of it as kind of aspect-oriented way of adding more annotations during runtime, to augment statically defined ones.
First define a mix-in annotation interface or class:
#JsonTypeInfo(use = Id.CLASS, include = As.PROPERTY, property = "class")
public interface FooMixIn {
}
Then configure ObjectMapper to use the defined interface as a mix-in for your POJO:
ObjectMapper mapper = new ObjectMapper().addMixIn(Foo.class, FooMixIn.class);
All annotation sets that Jackson recognizes can be mixed in. For more details, have a look at the Jackson documentation.

Jackson with JSON: How can I make it ignore additional properties but error on incomplete json?

I know how I can make Jackson to ignore any additional fields in Json, simply by adding
#JsonIgnoreProperties(ignoreUnknown = true):
#JsonIgnoreProperties(ignoreUnknown = true)
class MyDto {
int someField;
}
But side-effect of this is that Jackson now also accepts incomplete JSON and fills missing fields with nulls.
How can I enforce Jackson to require every field to exist in json and still ignore additional fields in it?
Thank you.

Jackson explicitly does NOT validate logical POJO contents; instead, you are recommended to use Bean Validation (JSR-303, see http://en.wikipedia.org/wiki/Bean_Validation) API implementation; for example one provided by Hibernate project: http://hibernate.org/validator/
This is the approach many frameworks take; for example, DropWizard supports data-binding using Jackson, and then validation (after data-bind, before business logic run) using Bean Validation.

In order to check if all properties needed are available you need to add the required anotation to the property.
#JsonProperty(value = "response", required = true)
public SomeResponse response;

How to deserialize interface fields using Jackson's objectMapper?

ObjectMapper's readValue(InputStream in, Class<T> valueType) function requires the Class. But how do I use it if the class I am passing internally, is having some Interface as data member.
although I can understand the reason behind this exception, as Jackson is not getting the concrete class of the internal Interface of the passed class, but my question is how to resolve it?
how do I deserialize it then? The class I am trying to deserialize is:
class BaseMetricImpl<N> implements Metric<N> {
protected MetricValueDescriptor descriptor;
}
Here MetricValueDescriptor is an interface, so this gives me following error : -
com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of MetricValueDescriptor, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information
at [Source: java.io.ByteArrayInputStream#2ede2c9f; line: 1, column: 2] (through reference chain: SingleValueMetricImpl["descriptor"])
at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
at com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:624)
at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:115)
at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375)
at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2793)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1989)

Jackson obviously cannot construct the MetricValueDescriptor object since it is an interface. You will need to have additional information in your json and in your ObjectMapper to tell jackson how to construct an object out of it. Here is one way to do it, assuming MVDImpl is a concrete class which implements MetricValueDescriptor:
You can tell Jackson the required type information through a field in the json itself, say "type". To do this, you need to use JsonTypeInfo and JsonSubTypes annotations in your interface. For example,
#JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.PROPERTY,
property = "type")
#JsonSubTypes({
#Type(value = MVDImpl.class, name = "mvdimpl") })
interface MetricValueDescriptor
{
...
}
You will need to add a "type":"mvdimpl" field in your json as well.
I was going to point you to the official doc for more info, but then I found an excellent blog covering this topic - Deserialize JSON with Jackson. It covers this topic pretty comprehensively and with examples. So you should definitely read it if you need more customisation.

I see it going one of two ways, but they both require you manually create a concrete class that implements your interface.
Use #Hari Menon's answer and use #JsonSubTypes. This works if you can introduce a type field or something else to trigger which implementation to use.
Use #JsonDeserialize to tell jackson what concrete class it uses by default.
#JsonDeserialize(as = MVDImpl.class)
interface MetricValueDescriptor
{
...
}
Here's a more thorough explanation: https://zenidas.wordpress.com/recipes/jackson-deserialization-of-interfaces/
And the docs: https://fasterxml.github.io/jackson-databind/javadoc/2.8/com/fasterxml/jackson/databind/annotation/JsonDeserialize.html

You don't need to alter the code, you can set it programmatically on the mapper:
static setup() {
final var simpleModule = new SimpleModule()
.addAbstractTypeMapping(<Interface>.class, <Implementation>.class);
objMapper = new ObjectMapper()
.registerModule(new Jdk8Module()) // You probably want this as well
.registerModule(simpleModule);
}

Java Jersey use GET to return JSON that returns only some fields instead of all

Does naybody knows a way to use Jersey's GET method to return a JSON that returns only some fields of an entity instead of all?
Does anybody know a way to use Jersey's GET method to return a JSON that returns only some fields of an entity instead of all?
E.g. in the following class I want to receive (with POST) values for 'name' and for 'confidential', buy while returning (with GET) I only need 'name' value, not 'confidential'.
#Entity
#Table(name = "a")
#XmlRootElement
#JsonIgnoreProperties({"confifentialInfo"})
public class A extends B implements Serializable {
private String name;
#Basic(optional = false)
private String confifentialInfo;
// more fields, getters and setters
}

If you are using the JAXB approach, you can mark fields with #XmlTransient to omit them. If you are using POJO mapping or want to exclude fields only for some requests, you should construct the JSON with the low level JSON API.

If you are using Jackson, you can use the annotation #JsonIgnore for methods
Marker annotation similar to javax.xml.bind.annotation.XmlTransient
that indicates that the annotated method is to be ignored by
introspection-based serialization and deserialization functionality.
That is, it should not be consider a "getter", "setter" or "creator".
And #JsonIgnoreProperties for properties
Annotation that can be used to either suppress serialization of
properties (during serialization), or ignore processing of JSON
properties read (during deserialization).

Jackson equivalent to #XmlSeeAlso

I am writing a RESTful web service using Java and Jersey, where the service will accept either XML or JSON inputs. Jackson is used as the JSON deserializer, and integrated into the Jersey config.
One of the endpoints is a POST request to a URL, where the content can be one of several different Java classes, and there is a common base class. These classes - with XML annotations - are:
#XmlRootElement(name = "action")
#XmlAccessorType(XmlAccessType.NONE)
#XmlSeeAlso({ FirstAction.class, SecondAction.class, ThirdAction.class })
public abstract class BaseAction {
}
#XmlRootElement(name = "first-action")
#XmlAccessorType(XmlAccessType.NONE)
public class FirstAction extends BaseAction implements Serializable {
}
// Likewise for SecondAction, ThirdAction
In my resource I can declare a method like:
#POST
#Path("/{id}/action")
public Response invokeAction(#PathParam("id") String id, BaseAction action) {...}
Then I can POST an XML fragment that looks like <firstAction/> and my method will be invoked with a FirstAction instance. So far so good.
Where I'm struggling is getting the JSON deserialization to work as seamlessly as the XML deserialization. Where the #XmlSeeAlso annotation was critical to get the XML deserialization working properly, it seemed that the equivalent for JSON was #JsonSubTypes. So I annotated the classes like this:
// XML annotations removed for brevity, but they are present as in the previous code snippet
#JsonSubTypes({ #JsonSubTypes.Type(name = "first-action", value = FirstAction.class),
#JsonSubTypes.Type(name = "second-action", value = SecondAction.class),
#JsonSubTypes.Type(name = "third-action", value = ThirdAction.class) })
public abstract class BaseAction {
}
#JsonRootName("first-action")
public class FirstAction extends BaseAction implements Serializable {
}
// Likewise for SecondAction, ThirdAction
I then feed it my test input: { "first-action": null } but all I can get is:
"org.codehaus.jackson.map.JsonMappingException: Root name 'first-action' does not match expected ('action') for type [simple type, class com.alu.openstack.domain.compute.server.actions.BaseAction]"
Unfortunately since I'm trying to be compatible with someone else's API I can't change my sample input - { "first-action": null } has to work, and deliver to my method an object of class FirstAction. (The action doesn't have any fields, which is why null shouldn't be a problem - it's the type of the class that's important).
What's the correct way to have the JSON deserialization work in the same way as the XML deserialization already is?

If you are using Jackson, you are looking for #JsonTypeInfo and #Type . Please see here for more information

JSON does not work the way XML does, so the solution is not identical.
What you need to use is (like the other answer said), #JsonTypeInfo. That only triggers inclusion and use of the type identifier. If so, then '#JsonSubTypes` will be of use in deserialization.
The reason this indicator must be used is simple: if you have more than one alternative type to deserialize to, there must be something to differentiate.
Note, too, that this does NOT have to be a property -- while most users choose "As.PROPERTY" inclusion, it is not (IMO) the best way. "WRAPPER_OBJECT" may be what you are looking for, as it adds an extra intermediate JSON property, which is somewhat similar to what XML does.

I investigated the use of #JsonTypeInfo but ran into problems because I could not alter the input format. The parser absolutely had to be able to handle input { "first-action":null }. This ruled out the possibility of adding an #type or #class property. Using a wrapper object may have worked, but it choked on the null payload.
A crucial point was that I was using the UNWRAP_ROOT_PROPERTY configuration option. Jackson was absolutely insisting on finding an action property and I could not get it to consider anything else. So, I had to selectively disable UNWRAP_ROOT_PROPERTY for certain domain objects, so that Jackson would be open to parsing alternatives. I modified the project's ContextResolver.getContext(...) implementation to check for a #JsonRootName annotation - since this only has meaning if wrapping is enabled, I used the presence of this annotation to determine whether to return an object mapper configured with root property wrapping on, or off.
At this stage, I might have been able to use #JsonTypeInfo(include=JsonTypeInfo.As.WRAPPER_OBJECT, ...), except for the issue with the null payload mentioned above (this is used to indicate that the child object has no properties - if the spec I was working from had given an empty object {} instead then there would not be a problem). So to proceed I needed a custom type resolver.
I created a new class that extended org.codehaus.jackson.map.TypeDeserializer, with the purpose that whenever Jackson is called to deserialize a BaseAction instance, it will call this custom deserializer. The deserializer will be given a subtypes array, which for BaseAction maps first-action, second-action, etc. to FirstAction.class, etc. The deserializer reads the input stream for the field name, then matches the name to a class. If the next token is an object, then it finds and delegates to the appropriate deserializer for that class, or if it is null it finds the no-args constructor and invokes it to get an object.
A class that implements org.codehaus.jackson.map.jsontype.TypeResolverBuilder is needed that can build an instance of this previous class, and then the TypeResolverBuilder is given as a #JsonTypeResolver annotation on the BaseAction class.