Jackson deserializing custom classes in an OSGi environment - osgi

Question

I have some trouble using Jackson 2.1 in an OSGi environment, when deserializing a class that way:
ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(new File("user.json"), User.class);
class User {
public Class clazz = org.example.MyClass.class;
}
Because Jackson is in a different bundle as my custom classes I want to deserialize, I often get a java.lang.ClassNotFoundException - usually on MyClass1 or MyClass2.
I traced it back to the class com.fasterxml.jackson.databind.util.ClassUtil which uses Class.forName(..) for retrieving a class for deserializing. Because of the different class-loaders on OSGI it only sees the classes of the JRE and of Jackson but not my custom classes.
Is there a simple way to make Jackson find all the required custom classes (I have dozens of them), e.g by adding a class-loader?

Answer 1

As the client of Jackson you have visibility of the classes that you want to deserialize into. The trick is to pass these classes into Jackson, rather than force Jackson to use dynamic reflection to find the classes.
The Jackson documentation indicates that the method ObjectMapper.readValue can take a Class object as its parameter. If you use this method then Jackson should not need to call Class.forName(). The docs give the following example:
ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(new File("user.json"), User.class);
Here, User is the domain class which is visible to your client but not to Jackson. This invocation should work fine in OSGi... if it does not then I would suggest Jackson may have a bug.