Spring Autowiring Failure: Top Fixes

There are several possible reasons for the failure of @Autowired injection:

1. The dependent Bean was not scanned by the Spring container: This could be due to the Bean not being configured properly or not having the @Component or @Repository annotations added.
2. There are multiple beans of the same type: When there are multiple beans of the same type, the Spring container cannot determine which bean to inject. You can use the @Qualifier annotation to specify the specific bean to inject.
3. The types do not match: the injected field type does not match the type of the bean being injected, this can be resolved by adding @Qualifier annotation to the field or using @Resource annotation to specify the injected bean.
4. Circular dependency: If there is a situation of circular dependency, where A depends on B and B depends on A, the Spring container is unable to resolve the circular dependency issue, which will result in injection failure.
5. Configuration error: injection may fail due to errors in the configuration file, such as forgetting to add the context:component-scan tag in the configuration file or incorrect configuration.
6. If the scope of the field being injected is prototype and the scope of the Bean being injected is singleton, the injection will fail due to conflicting scopes.
7. Injection sequence issue: If the creation sequence of injected beans occurs after the creation of the fields they are injected into, injection will fail. You can specify dependency relationships using the @DependsOn annotation.

These are common reasons for the failure of @Autowired injection, it is necessary to carefully check the configuration and code to ensure that the above problems do not occur.