Configuring Type Information Inclusion and Exclusion

When working with Jackson, a popular Java library for JSON processing, you may often come across scenarios where you need to control which type information should be included or excluded during serialization and deserialization processes. In this article, we will explore various ways to configure type information inclusion and exclusion in Jackson.

Type Information Inclusion

Type information inclusion refers to the process of including metadata about the actual Java types of objects when serializing or deserializing them. This information can be useful, especially when dealing with polymorphic types, as it allows Jackson to correctly map JSON data to their corresponding Java types.

Including Type Information for Serialization

To include type information during serialization, you can make use of the @JsonTypeInfo annotation at both the class-level and property-level.

At the class level, you can annotate your classes with @JsonTypeInfo to specify the type inclusion mechanism, such as using a class name, custom name, or none at all. For example:

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class")
public class MyPojo {
    // class fields and methods
}

This configuration ensures that the class name will be included as the value of the @class property in the serialized JSON.

Alternatively, you can use the property-level @JsonTypeInfo annotation to include type information for a specific property only. For example:

public class MyPojo {
    @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class")
    private MyType myProperty;
    // other fields and methods
}

In this case, only the myProperty field will include the type information.

Including Type Information for Deserialization

Similar to serialization, you can also include type information during the deserialization process. To achieve this, you need to use the same @JsonTypeInfo annotation but with a different configuration.

For example, let's assume you have the following JSON data:

{
  "@class": "com.example.MyPojo",
  "myProperty": {
    // ...
  }
}

To deserialize this JSON and include type information, you can annotate your class or property as shown in the previous section.

Type Information Exclusion

While including type information can be useful in certain scenarios, there might be cases where you want to exclude type information for security or simplicity purposes.

Excluding Type Information for Serialization

To exclude type information during serialization, you can use the @JsonIgnoreProperties annotation. This annotation allows you to specify which properties or classes should be ignored during serialization and deserialization.

For example, let's assume you have a class MyPojo but you do not want to include type information for it:

@JsonIgnoreProperties(value = { "@class" })
public class MyPojo {
    // other fields and methods
}

By annotating the class with @JsonIgnoreProperties, you can exclude the @class property from being serialized.

Excluding Type Information for Deserialization

To exclude type information during deserialization, you can use the @JsonIgnoreType annotation. This annotation allows you to specify which types should be ignored during the deserialization process.

For example, let's say you have the following JSON data:

{
  "@class": "com.example.MyPojo",
  "myProperty": {
    // ...
  }
}

But you do not want to deserialize the myProperty field with its actual type, you can use the @JsonIgnoreType annotation as follows:

@JsonIgnoreType
public class MyType {
    // other fields and methods
}

By annotating the MyType class with @JsonIgnoreType, you can exclude it from being deserialized with its actual type.

Conclusion

In this article, we discussed how to configure type information inclusion and exclusion in Jackson. We explored various annotations, such as @JsonTypeInfo, @JsonIgnoreProperties, and @JsonIgnoreType, which allow us to control the level of type information included or excluded during serialization and deserialization processes. It is important to choose the appropriate configuration based on the requirements of your application to ensure secure and efficient JSON processing with Jackson.