Скачать или смотреть Solving the Bean not found from another module Issue in Spring Boot

A comprehensive guide to resolving the `Bean not found from another module` issue in Spring Boot, featuring practical solutions and best practices for organizing your Maven project.
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Troubleshooting the Bean Not Found Error in Spring Boot

If you are working with a Spring Boot application and encounter the dreaded Bean not found from another module issue, you're not alone. This is a common challenge that developers face, especially when dealing with multi-module projects in Maven. In this post, we will explore the problem in detail and provide a clear, organized solution to help you get back on track.

Understanding the Problem

Let's start by summarizing the issue:

Project Structure

You may have a project that looks something like this:

myProject:

moduleA ← has dependencies on moduleB and moduleC

moduleB ← has no dependency

moduleC ← has a dependency on moduleB

In this scenario, you have defined two interfaces in moduleB: the Greeting interface, which is implemented by HelloWorld located in moduleB, and the Messages interface, which is implemented by MessagesImpl in moduleC. However, when you run your application, you might see an error indicating Spring cannot find the bean of type Messages.

Common Issues

The root cause of this issue often lies in the way Spring initializes and scans for components across different modules. Here are some common pitfalls:

Missing @ ComponentScan annotations

Improper module dependencies

Incorrect usage of auto-configuration

Implementing the Solution

Now that we understand the problem let's discuss the solution step-by-step.

1. Configuration Class

First, each library (or module) should include a configuration class at the top package level. This class is essential for component scanning and should include the @ ComponentScan annotation.

Example:

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2. Auto-Configuration Setup

To ensure that your library modules are properly recognized by Spring, you can leverage Spring Boot's auto-configuration feature. There are two main ways to do this:

Method 1: Using spring.factories

Create a file named spring.factories in the src/main/resources/META-INF directory of your module. Add the following content:

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This file tells Spring Boot to automatically configure your library when the application starts.

Method 2: Manual Import

If you prefer not to use the auto-configuration method, you can manually import your configuration class in the main application configuration class:

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3. Best Practices

While both methods are effective, we recommend the auto-configuration approach for modules. Here’s why:

Less Messy: Automatic configuration keeps your code clean and modular.

Increased Control: You can explicitly define which beans are loaded without relying on global @ ComponentScan.

Final Notes

After applying these changes, run your application again. The Bean not found error should be resolved, and your module should successfully recognize the implementation of the Messages interface from moduleC.

By following this structured approach, you'll be better equipped to handle similar issues in the future. Don't forget that managing dependencies and configurations across multiple modules can be challenging, but with the right setup, it becomes a manageable task.

Conclusion

In summary, if you're facing the Bean not found from another module error in your Spring Boot applications, ensure you have a proper configuration class and consider using auto-configuration for your modules. These steps will help streamline your application architecture and avoid common pitfalls.

Happy coding!