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Solving UnrecognizedField Errors in Java: A Guide to Proper Annotations with Jackson and Gson

Learn how to fix the `Unrecognized field` error in Java when deserializing JSON by using the correct annotations with Jackson and Gson. --- This video is based on the question https://stackoverflow.com/q/71069500/ asked by the user 'l0r3nz4cc10' ( https://stackoverflow.com/u/693233/ ) and on the answer https://stackoverflow.com/a/71069701/ provided by the user 'Alexandru Severin' ( https://stackoverflow.com/u/2342529/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Unrecognized field during deserialization despite @SerializedName annotation Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Understanding the UnrecognizedField Error in Java When working with Java applications that interface with REST services, it's common to deal with JSON responses. However, one common issue developers encounter is the Unrecognized field during deserialization error. This can be frustrating, especially when you're sure that you've set everything up correctly. In this post, we'll examine this error, predominantly encountered while using Jackson for deserialization, and how to effectively resolve it. The Problem: An Example Error Let's take a closer look at an example of the error message that can appear during the deserialization process: [[See Video to Reveal this Text or Code Snippet]] This error is often seen when you try to map a JSON structure to your Java objects but have incorrect annotations or field names that do not match. In this case, the JSON response looks like this: [[See Video to Reveal this Text or Code Snippet]] Your Java class, HolderCollectionWrapper, is expecting to receive this JSON as a list of holders, but the field name does not match what Jackson expects due to your annotation usage. Analyzing the Code Here's the relevant piece of Java code responsible for handling the JSON response: [[See Video to Reveal this Text or Code Snippet]] The Issue with Annotations The key issue lies in the use of @SerializedName, which is a Gson annotation, while the code is attempting to use Jackson for serialization. Jackson requires different annotations to map field names correctly from the JSON data. The Solution: Use Jackson's @JsonProperty Annotation To resolve the Unrecognized field error, switch to using the appropriate Jackson annotation. Specifically, replace @SerializedName with @JsonProperty. This adjustment will correctly inform Jackson about the respective JSON field name. Revised Java Code Here is how the corrected part of your code will look: [[See Video to Reveal this Text or Code Snippet]] Summary of Key Steps Identify the Error: Recognize the UnrecognizedField error indicating a mismatch between the JSON field name and your Java properties. Check Annotations: Ensure that you're using the correct annotations for the library you are working with. Use @JsonProperty for Jackson. Update Java Class: Replace @SerializedName with @JsonProperty to correctly map the field names from your JSON response. Conclusion By making the simple change to the annotation in your HolderCollectionWrapper class, you can effectively resolve the Unrecognized field issue. This issue highlights the importance of using the correct library practices, especially when dealing with JSON in Java. Following the steps provided in this blog can help streamline your development process and avoid common pitfalls associated with serialization and deserialization.