For Jackson, How to safely share an ObjectMapper ? Is there any immutable ObjectMapper?

Question

Mapper instances are fully thread-safe, there is no need to create a mapper for single use, but mapper's config can be changed.

Although ObjectMapper has copy function to duplicate the config for customize based on exists mapper, if I share a mapper, there is no guarantee that when someone want to customize the mapper, they will copy the shared mapper. So I want a immutable mapper to share, if someone accidently changed the shared mapper, some exception should be throw.

Is there something like this ?

Answer 1

One approach is to not share the ObjectMapper instance, but rather configure it correctly and then share instances of ObjectWriter and ObjectReader created by the ObjectMapper.

ObjectMapper om = new ObjectMapper();
// Configure to your needs
om.enable(...);
om.disable(...);

// Distribute these to the parts of the program where you fear configuration changes.
ObjectWriter writer = om.writer();
ObjectReader reader = om.reader();

This also seems to be the approach favoured by the developers of Jackson: https://stackoverflow.com/a/3909846/13075