Resolving @ Service Class Not Autowired Issue in Spring Boot Using MapStruct

Описание: A detailed guide on solving the `@ Service class not autowired` problem in your Spring Boot application when using MapStruct for JSON serialization. Learn best practices for your mapper and avoid common pitfalls.
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This video is based on the question https://stackoverflow.com/q/68457437/ asked by the user 'abubakirov' ( https://stackoverflow.com/u/16488888/ ) and on the answer https://stackoverflow.com/a/68460245/ provided by the user 'Filip' ( https://stackoverflow.com/u/1115491/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving @ Service Class Not Autowired Issue in Spring Boot Using MapStruct

When developing with Spring Boot, you might encounter various dependency injection issues, one common challenge being the failure of a service class to autowire correctly within a MapStruct mapper. This problem often leads to NullPointerExceptions (NPEs) when you attempt to access the service methods. In this guide, we will explore the reasons behind this issue and provide a structured solution to avoid it.

Understanding the Problem

Let's break down the problem as outlined in the original question. You are trying to implement JSON serialization in your Spring Boot application using MapStruct. You have a mapper class that relies on a service class (annotated with @ Service) to execute some mapping logic after certain operations (often referred to as 'aftermapping'). However, the service dependency is not being injected into the mapper class, causing the application to throw a NullPointerException.

Example of the Error Scenario

In the provided code snippet, the InstrumentMapper class tries to call the method marketDataService.findMarketByCode(...) but fails because marketDataService is null. This leads to the NPE:

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Solution Overview

The root cause of the issue is that the factory Mappers does not support dependency injection when using a non-default component model. Here is a step-by-step guide on how to resolve this issue.

Step 1: Inject the Mapper into the Service

Instead of using Mappers.getMapper(InstrumentMapper.class) within your MarketDataService, directly inject the mapper into your service class. This ensures that Spring manages the mapper and provides the necessary context for dependency injection. Here’s an example of how to update your service class:

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Step 2: Update the Mapper

The next step involves refining your InstrumentMapper class. You don't need to use expressions in your mappings if the target property names are the same as the source. Instead, you can use the source attribute. Here’s the refactored version of your mapper:

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Step 3: Handle Cyclic Dependencies

While making such adjustments, be cautious of potential cyclic dependencies where the mapper might depend on the service, and the service might depend back on the mapper. This can lead to StackOverflowError. You can avoid cycles by refactoring your design, such as extracting common logic into a helper class.

Conclusion

By changing the way you inject your mapper into other components and refining your mapper methods, you can effectively resolve the @ Service class not autowired issue in a Spring Boot application using MapStruct. Always remember to keep your component dependencies clean to avoid cyclic issues and ensure your mapping configurations are optimal.

Following these steps should help you overcome dependency injection issues in your Spring Boot applications using MapStruct easily. Happy coding!