The “unsatisfied dependency expressed through constructor parameter” error is a common one when using dependency injection frameworks such as Spring. This error occurs when a required bean is not found in the application context. There are two common causes of this error:
- The required bean is not defined in the application context.
- The required bean is defined in the application context, but it is not of the correct type.
This error can be tricky to debug, but there are some tools and techniques that can help. In this article, we’ll look at what causes this error and how to debug it.
What is an unsatisfied dependency?
An unsatisfied dependency is a parameter in a constructor that is not satisfied by any of the available values. This can happen when a class is instantiated without providing all the required information, or when a required value is not provided in the correct format.
In either case, the resulting object will not be able to function properly and will usually throw an error when used. To avoid this, always make sure that all dependencies are satisfied before instantiating an object.
Why do we get them?
There are many reasons why you may see this error, but the most common is that you’re trying to inject a dependency into a constructor, but that dependency isn’t defined in your application’s context. When this happens, Spring can’t satisfy the dependency and throws this exception.
How can we fix them?
There are a few ways to fix unsatisfied dependency problems:
- Use @Autowired on your constructor parameters. This tells Spring to inject a bean of the correct type into your constructor when creating the bean.
- Use @Qualifier(“beanName”) on your constructor parameters. This tells Spring to inject a bean with the given name into your constructor when creating the bean. If you have multiple beans of the same type, this is how you tell Spring which one to inject.
- Use @Resource(“beanName”) on your constructor parameters. This tells Spring to inject a bean with the given name into your constructor when creating the bean. If you have multiple beans of the same type, this is how you tell Spring which one to inject.
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