How to use a @Autowired bean inside a constructor?

Question

Here is my class,

public class MyBusinessException extends RuntimeException {
    @Autowired
    private MessageSource messageSource;

    private String errorCode;

    private String messageInEnglish;

    public MyBusinessException(String errorCode){
       this.errorCode=errorCode;
       this.messageInEnglish=messageSource.getMessage(this.code,null, Locale.ENGLISH);
    }
}

This is an exception class.When I pass the errorCode as a parameter to constructor it should populate the error message,That`s what I am looking for.Infact I want to instantiate the class like this

throw new MyBusinessException("MY-ERROR-CODE");//want to initiate like this(only one argument for constructor)

How to achieve something like this?

All these I have tried so far:

Constructor Autowiring.
Using @PostConstruct

what is happening when you do new MyBusinessException(...) now? — pvpkiran
– pvpkiran, Commented Jan 29, 2018 at 12:26
why would you do that? by just storing the errorcode you have all you need — Stultuske
– Stultuske, Commented Jan 29, 2018 at 12:26

davidxxx · Accepted Answer · 2018-01-29 12:55:41Z

5

throw new MyBusinessException("MY-ERROR-CODE");//want to initiate like this(only one argument for constructor)

You cannot use @Autowired with objects that are not created by Spring.
I think that you should refactor your code to provide to MyBusinessException constructor all information that needs.
You don't need to couple it with Spring.

The logic that is Spring dependent :

@Autowired
private MessageSource messageSource; 
...
messageSource.getMessage(this.code,null, Locale.ENGLISH);

could be moved to a Spring bean that will create a fully initialized MyBusinessException instance.
Besides, messageSource.getMessage(this.code,null, Locale.ENGLISH) may be required for other exceptions. Moving it this logic in a specific class makes sense.

@Bean
public class ExceptionFactory{
   @Autowired
   private MessageSource messageSource; 

   public MyBusinessException createMyBusinessException(String errorCode){        
      return new MyBusinessException(errorCode, messageSource.getMessage(this.code,null, Locale.ENGLISH));        
  } 
}

You can note that createMyBusinessException() provides a simple API for the clients : they need to pass only the error code String to create the exception.
The MessageSource dependency is a implementation detail that they don't need to bother with.

For example, this is enough :

throw exceptionFactory.createMyBusinessException("MY-ERROR-CODE");

edited Jan 29, 2018 at 12:55

answered Jan 29, 2018 at 12:31

davidxxx

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2 Comments

Yannic Bürgmann Over a year ago

Like your solution since you have to write the code to find the message only one time instead of n-times for every instantiation of MyBusinessException

davidxxx Over a year ago

Thank you. In your code, the statements to find the message are also performed a single time : in MyBusinessException constructor. The advantages of the current solution are rather : 1) separation of concerns : messageSource.getMessage(this.code,null, Locale.ENGLISH) may be required for other exceptions. Moving it this logic in a specific class makes sense. 2) Simplified API for the client : you don't need to pass at each time two parameters to create the exception. Just the error code string is enough.

Yannic Bürgmann · Accepted Answer · 2018-01-29 12:54:35Z

3

Dependency Injection does only work for instances that are created by Spring.

Since you manually initialize your exception you need to inject the MessageSource to the @Component throwing this exception.

Then you could either pass the MessageSource to the constructor of your MyBusinessException or get the message in the desired language and pass this message to the constructor.

@Component
public class MyComponentDoingBusinessLogic {

    private MessageSource messageSource;

    @Autowired
    public MyComponentDoingBusinessLogic(MessageSource messageSource) {
      this.messageSource = messageSource;
    }

    public void someBusinessLogic() {
      //Doing something
      if (errorState) {
        throw new MyBusinessException(yourErrorCode, messageSource);
      }
    }
}

edited Jan 29, 2018 at 12:54

answered Jan 29, 2018 at 12:35

Yannic Bürgmann

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3 Comments

SeverityOne Over a year ago

How are you going to initialise anything if the exception isn't created by Spring?

Yannic Bürgmann Over a year ago

added a small sample to make more clear what i described

davidxxx Over a year ago

@Yannic Klem Your solution is valid and not so bad at all :)

OhadR · Accepted Answer · 2018-01-29 12:29:45Z

1

You cannot use @Autowired inside the ctor, as it was not yet initializaed by Spring.

The right way to do so, is to implement InitializingBean, which is basically Spring's ctor, and there (afterPropertiesSet method) you can use your injected fields.

answered Jan 29, 2018 at 12:29

OhadR

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1 Comment

XDS Over a year ago

This should probably be marked as the correct answer.

SeverityOne · Accepted Answer · 2018-01-29 12:36:22Z

0

You can't do it this way. An exception is constructed when it is thrown, which means that it won't get initialised by Spring. What you could do is to use a static method to get the current Spring application context, and get your bean from there.

Whether or not this is a clean solution is another issue, but you didn't ask about that.

answered Jan 29, 2018 at 12:36

SeverityOne

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