Serialization and Deserialization of Polymorphic types in Spring Boot using Jackson

Visitor pattern on JSON objects.

This simple app shows an example how serialize class with preserving its type, and then use this information to deserialize. This example introduces interface Animal and two implementations: Lion and Rat.

Running application

To run this application simply start main method in com.cohesiva.deserialize.Application or invoke command line:

mvn clean install
java -jar target/deserialize-polymorphic-0.0.1-SNAPSHOT.jar

Testing serialization

This application serves few rest endpoinds. To fetch whole zoo invoke:

curl -s http://localhost:8080/zoo

As you can see in response each animal object contains property @class, which contains java class name.

{
    "animals": [
        {
            "@class": "com.cohesiva.deserialize.web.model.Lion",
            "name": "Gerard, King of the Jungle",
            "lionessNo": 2
        },
        {
            "@class": "com.cohesiva.deserialize.web.model.Rat",
            "name": "Boghdan, One of many"
        }
    ]
}

This behaviour is enabled because Animal class is annotated with:

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class")

Testing deserialization

Hit this url with post to add new animal to zoo.

 curl -s -H "Content-Type: application/json" -X POST -d '{"name": "Tom", "lionessNo": 5, "@class": "com.cohesiva.deserialize.web.model.Lion"}' http://localhost:8080/animals

This invokes visitor service ZooService, and prints on console:

Locking lion Tom, King of the Jungle with 5 lioness

Gotcha

It's not all so pretty. Hit this endpoint:

curl -s http://localhost:8080/animals

Class information is missing due to java type erasure. To see more about this behaviour see this issue.