Ignoring Null Fields during Serialization with Jackson

Jackson is a popular JSON processing library for Java that provides a lot of flexibility and customization options. One common requirement when serializing objects to JSON is to ignore fields that have null values. In this tutorial, we will explore how to achieve this using Jackson.

Introduction to @JsonInclude

The @JsonInclude annotation is used to specify which properties of an object should be included or excluded during serialization. It can be applied at the class level or at the field level. The @JsonInclude annotation has several options, including:

• Include.NON_NULL: Includes only non-null values.
• Include.ALWAYS: Includes all values, even null ones.

Configuring @JsonInclude at Class Level

To ignore null fields for an entire class, you can apply the @JsonInclude annotation at the class level. Here’s an example:

@JsonInclude(JsonInclude.Include.NON_NULL)
public class SomeClass {
    private String someValue;
}

In this case, if someValue is null, it will be excluded from the JSON output.

Configuring @JsonInclude at Field Level

You can also apply the @JsonInclude annotation at the field level to override the default behavior. Here’s an example:

public class SomeClass {
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private String someValue;
}

This will achieve the same result as applying the annotation at the class level.

Using ObjectMapper Configuration

Alternatively, you can configure the ObjectMapper instance to ignore null fields for all objects being serialized. Here’s an example:

ObjectMapper mapper = new ObjectMapper();
mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);

This will apply the configuration globally and exclude null values from the JSON output.

Mixing Class-Level and Field-Level Configurations

You can mix class-level and field-level configurations to achieve more complex serialization behavior. For example:

@JsonInclude(JsonInclude.Include.NON_NULL)
public class SomeClass {
    private String someValue;
    
    @JsonInclude(JsonInclude.Include.ALWAYS)
    private String anotherValue;
}

In this case, someValue will be excluded if it’s null, while anotherValue will always be included, even if it’s null.

Conclusion

Ignoring null fields during serialization with Jackson is a straightforward process that can be achieved using the @JsonInclude annotation or by configuring the ObjectMapper instance. By applying these configurations at the class level or field level, you can customize the serialization behavior to suit your specific needs.