Recently, I was using the generator plugin to generate mybatis code and encountered Could not autowire. No beans of 'xxx' type found. Abnormal

I recently ran into an interesting problem in development where I was using the "generator" plugin to generate MyBatis code. However, during use, I suddenly encountered an exception: "Could not autowire. No beans of 'xxx' type found." (Cannot be automatically injected, cannot find 'xxx' type bean). Here, I will share with you how I solved this problem.

First, let's look at the background of this anomaly. In the Spring framework, autowiring is a very powerful feature that helps us automatically handle dependency injection. When we use the @Autowired annotation in the code, the Spring framework will automatically find the matching bean in the container and inject it into the corresponding variable. However, when the framework cannot find a matching bean, it throws a "Could not autowire. No beans of 'xxx' type found." exception.

There are several possible causes for this exception. First, we need to check that our code configures the bean correctly. In the Spring framework, we can use the @Configuration annotation to specify a class as a configuration class, and use the @Bean annotation to declare a bean. We need to make sure that our configuration classes are loaded correctly and that all beans that need to be injected are properly declared.

Secondly, we also need to check whether there are beans in our code that meet the requirements of autowiring. Sometimes, we may forget to declare a bean in the code, or we may not configure the bean correctly in the container. We can ensure that all required beans are created and declared correctly by checking our code and configuration files.

After solving the above problems, we also need to check whether there is a bean naming problem in our code. Sometimes, we may use the wrong bean name in the code, or our bean name does not match the name in the configuration file. We need to make sure that the bean name we use in the @Autowired annotation matches the actual bean name.

Finally, we can also use debugging tools to help us locate problems. For example, we can add logging output to our code to see what the Spring framework is doing while autowiring. We can also use the debugger to step through the code and observe the values ​​of variables and method calls. These tools can help us better understand the execution process of the code and identify problems.

Below is a sample code showing how to autowire beans using the @Autowired annotation:

@Configuration
public class AppConfig {
    @Bean
    public XxxBean xxxBean() {
        return new XxxBean();
    }
}

@Service
public class MyService {
    @Autowired
    private XxxBean xxxBean;
    
    // ...
}

In the above code, we use the @Configuration annotation to mark the AppConfig class as a configuration class, and use the @Bean annotation to declare a bean named xxxBean. Then, in the MyService class, we use the @Autowired annotation to automatically inject xxxBean into the xxxBean variable.

By carefully checking the code, configuration files and usage of annotations, and using debugging tools to troubleshoot, I finally successfully resolved the "Could not autowire. No beans of 'xxx' type found." exception.

When encountering "Could not autowire. No beans of 'xxx' type found." exception, another possible reason is that multiple configuration files or modules are used in the project, and related beans are not correctly declared and introduced.

In this case, we need to ensure that the relevant modules are correctly imported in the main configuration file. Normally, we can use the @ComponentScan annotation to specify the package path we want to scan, and automatically introduce the components and beans in it. If our modules are located in different packages, we need to add multiple @ComponentScan annotations in the main configuration file to scan different package paths.

Below is a sample code showing how to use the @ComponentScan annotation to scan multiple package paths:

@Configuration
@ComponentScan(basePackages = {"com.example.module1", "com.example.module2"})
public class AppConfig {
    // ...
}

In the above code, we use the @ComponentScan annotation to scan components and beans in the two package paths "com.example.module1" and "com.example.module2".

In addition, we also need to ensure that the relevant dependency packages are correctly introduced into our project. Sometimes, if we forget to add dependencies in the project's build configuration file, or the version of the dependencies is not compatible with the framework we are using, it may also cause "Could not autowire. No beans of 'xxx' type found." abnormal.

So, to solve this problem, we need to check whether the correct dependencies are added in the project's build configuration file (such as Maven or Gradle). We can use the corresponding official documentation or dependency repositories to confirm the required dependencies and make sure their versions are compatible with our project.

To sum up, when encountering "Could not autowire. No beans of 'xxx' type found." exception, we need to check the following aspects:

1. Make sure that the beans that need to be injected are correctly declared in the code, and the @Configuration and @Bean annotations are correctly configured.
2. Check that the correct bean name is used in the code and that the name used in the @Autowired annotation is consistent with the actual bean name.
3. Make sure that the relevant dependencies are correctly introduced in the project and that the versions are compatible with the project's framework.
4. For multi-module projects, make sure to use the @ComponentScan annotation in the main configuration file to correctly import related modules.

I hope my sharing can help other developers to solve similar problems faster. Remember, when we encounter problems during the development process, patience and carefulness are the key to solving the problem!