Java Community | Help. Code. Learn.•2d ago

[Spring] Should I have a custom Objectmapper as a static attribute in my service class?

Currently have an Objectmapper, from the JSON jackson serialization api, from my configuration class used in my Service class. Using lombok, realized the @AllArgsConstructor doesn't create a constructor for static attributes. It makes sense to have it be static in the conventional sense, since it should be shared between service instances. It is making it hard to do unit tests. As best practice, should I be having the objectmapper attribute in my service class be static or not? I'm thinking I can forgo making it static since I'm getting a universal Objectmapper from the spring context anyway. Would appreciate the help.

10 Replies

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dan1st•2d ago

Why should a constructor initialize static fields via a parameter? Then they would be overwritten every time you create a new instance from the docs of ObjectMapper

Mapper instances are fully thread-safe provided that ALL configuration of the instance occurs before ANY read or write calls.

https://fasterxml.github.io/jackson-databind/javadoc/2.7/com/fasterxml/jackson/databind/ObjectMapper.html If you want to share the same configuration for all instances and never change its configuration afterwards, you can make the ObjectMapper static and you probably want to initialize it in a static initializer block or similar

public class YourClass {
  private static final ObjectMapper mapper;
  static {
    mapper = ...;
    //initialize the ObjectMapper here and configure it
  }
}

public class YourClass {
  private static final ObjectMapper mapper;
  static {
    mapper = ...;
    //initialize the ObjectMapper here and configure it
  }
}

public class YourClass {
  private static final ObjectMapper mapper = createObjectMapper();
  private static ObjectMapper createObjectMapper() {
    ObjectMapper created = ...;
    //configure it
    return created;
  }
}

public class YourClass {
  private static final ObjectMapper mapper = createObjectMapper();
  private static ObjectMapper createObjectMapper() {
    ObjectMapper created = ...;
    //configure it
    return created;
  }
}

Ghostyjangle•2d ago

oh sorry I forgot to mention that I want to have spring autowire the objectmapper instance to my service class. Or is this not the way I should do it?

dan1st•2d ago

in that case, don't make it static But isn't it normally the case that service classes are singletons?

Ghostyjangle•2d ago

I see it as being such that I can just change the objectmapper for some reason, I can just change it in the designated spring config class fundamentally its weird for objmapper to not be static from what you mentioned, but other than that, are there any implications that I'm missing by not making it static?

dan1st•2d ago

not really except that it isn't shared though it could still be shared if you have the same Spring context you'd just have multiple references to the same ObjectMapper you can't use it from static methods but it's really not a problem For Spring specifically, it's fine to make it non-static

Ghostyjangle•2d ago

ah right, I'll keep a note on that then, thanks for the help.

JavaBot•2d ago

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Ghostyjangle•2d ago

I'll close the post

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[Spring] Should I have a custom Objectmapper as a static attribute in my service class?