Spring Bean vs Spring Component

2018-12-30 579 words 3 mins read

The Difference Between @Bean and @Component and When to Use What?

This is the most common question that new as well as experienced Spring users get confused about. There are literally hundreds of questions on this Stackoverflow. This article will clear all the confusion.

Similarities between @Bean and @Autowired

@Bean

  • @Bean is an annotation based configuration and hence is used in @Configuration based class.
  • This is an explicit way of defining a bean and is also used on the methods defined in configuration class.

@Component - This is used in classes which you create in your app. This will only work after you enable component scan on the package that contains your class. - With component scan, Spring framework will scan the classpath and add all the classes that are marked with a @Component annotation. -This is also called the automated way of binding and discovering your bean.

So the bottom line is that both can do the job of wiring your bean. It’s just that with @Bean you have to define each class explicitly and in case of @Component, Spring does this automatically for you. The @Bean way of wiring your bean is analogous to defining Beans in XML, prior to Spring 2.5. Now that you understand what each does(the end result is the same), let’s take a look at what is the difference between the two and when you should choose one over the other.

Difference between @Bean and @Autowired

Scenario: We have a jar file which contains different services ex - Address check service, credit check service etc. This jar file is shared by many different applications/companies Ex - AT&T wants to use Address validator service while FICO wants to use only credit check service.

If you use @Component on those service classes and use component scan in the application, then both AT&T and FICO applications will end up detecting credit check in case of AT&T and address validator in case of FICO. As a result, you would face one of the two problems - + You will end up adjusting the filter on the component scan. + In case you have classes sharing the same name by any chance then you would have to add qualifier otherwise application would complain that it found more than two classes were found with same bean name and will fail to run.

Hence, in this scenario, you should use @Bean

Scenario : You downloaded a jar file from GitHub and it is not using Spring. The jar file is a simple and basic java program. Your app wants to use this third-party jar file but since your application is using Spring while the third party jar is not, you will have to write new() keyword to access the functionalities. You want to wire the third party classes.

Say your class name is MyClass.java and you want to use ThirdPartyClass.java. In this case if you write


public class MyClass{
   .....
     @Autowired
     ThirdPartyClass thirdPartyClass;

}

Your code will throw NullPointerException if you try and access any method of class object thirdPartyClass. In this scenario, you should use @Bean.

Rule of Thumb

A simple way to decide between @Component and @Bean is that - if you want to use third-party classes or jar then use @Bean. - If you are writing your own classes for your application then use Component. - If you want to use a third party class or jar that is not written using Spring Component then use @Bean.


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