Expected at least 1 bean which qualifies as autowire candidate for this dependency

When developing a Spring application, one of the common errors that developers encounter is “Expected at least 1 bean which qualifies as autowire candidate for this dependency”. This error message is thrown by the Spring framework when it is unable to find a suitable bean to autowire a dependency. In this blog post, we will discuss the causes of this error and provide examples of how to troubleshoot and resolve it.



Root Cause

  1. Missing Bean Annotation: The most common cause of this error is that the bean class is missing the @Component, @Service, or @Repository annotation. These annotations are used to indicate that a class is a Spring bean and should be considered for autowiring.
  2. Missing Component Scan: If the @ComponentScan annotation is missing from the configuration class, Spring will not be able to find the bean classes and will throw this error.
  3. Wrong Package Name: If the package name specified in the @ComponentScan annotation is incorrect, Spring will not be able to find the bean classes and will throw this error.
  4. Bean Not Initialized: If the bean class is not initialized, Spring will not be able to find the bean and will throw this error.
  5. Check for typo in bean name: The bean name in the @Autowired annotation should match the name of the bean class. Check for any typo errors in the name.
  6. Check for circular dependencies: If two beans depend on each other, this can cause a circular dependency and lead to the “Expected at least 1 bean” error. To resolve this issue, you can either refactor your code to remove the circular dependency or use @Lazy annotation to break the circular dependency.
  7. Check for conflicting bean names: Spring allows multiple beans of the same type to be defined as long as they have different names. If there are multiple beans of the same type but with the same name, this can cause confusion for the autowiring process and lead to the “Expected at least 1 bean” error. To resolve this issue, you can give the beans different names or use the @Qualifier annotation to specify the bean to be used for autowiring.
  8. Check for missing dependencies: If a bean depends on another bean that is not available, this can lead to the “Expected at least 1 bean” error. To resolve this issue, you can check for any missing dependencies and include them in your project.

It’s always good to check your imports, package names, and beans name to make sure that you are autowiring the correct bean. Additionally, checking for circular dependencies and conflicting bean names can also help you resolve this error.



Exception Example

Let’s consider an example where we have a service class MyService which needs to autowire a DAO class MyDAO. The following is the error message we are getting:

org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.MyDAO' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}


Solution 1

Add @Component annotation to the MyDAO class, so that Spring will recognize it as a bean.

@Component
public class MyDAO {
    //...
}


Solution 2

Add @ComponentScan annotation to your configuration class and specify the package name of your bean classes.

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


Solution 3

Check the package name specified in the @ComponentScan annotation, it should be correct package name of your bean classes.

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


Solution 4

Check that the bean class is initialized and that the bean is not null

@Service
public class MyService {

    @Autowired
    private MyDAO myDAO;

    public void doSomething() {
        if(myDAO == null) {
            throw new IllegalStateException("MyDAO is not initialized");
        }
        //...
    }
}


Conclusion

In this blog post, we have discussed the causes of the “Expected at least 1 bean which qualifies as autowire candidate for this dependency” error in Spring and provided examples of how to troubleshoot and resolve it. By understanding the causes of this error and knowing how to troubles



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