Using only unchecked exceptions on your Java application

2 minute read

The Java checked exceptions are some kind of unique feature that most of the programming languages do not have. Is this could be a signal to not use it? The short answer is yes. And I will show how not use it.

The checked exceptions are considered a mistake and this conclusion is not new. This helps to explain why any modern language, like Scala or Kotlin, not copied this idea.

There are a lot of sources on the Internet explaining how checked exceptions are bad and the advantages to not use it. Just follow the links that I share before if you prefer. But my mission here is to show how you could organize your code to work only with unchecked exceptions.

Show me the code!

The big first step is to lose the notion to have many exceptions, representing a lot of different situations, like FileNotFoundException, OrderMissingException, InvalidEmailException, etc. Soon or later, you will have a bunch of very similar classes with the same purpose, not bringing with them any new information. And on this Rest API times, they will also need to be translated as a nice message for the final user some time, and these exceptions will not help you.

So, you just need a single exception extending RuntimeException. You can choose the name you prefer. Here I will call SystemException.

To represent the different “exceptions”, you can create error codes. This is easily done using enumerators, like:

public enum ErrorCode implements IErrorCode {
	
  INVALID_NAME(101),
  ORDER_NOT_FOUND(102),
  CREDIT_CARD_EXPIRED(103),
  VALUE_TOO_SHORT(104);

}

Every time you need to throw the exception, just pass the right error code:

throw new SystemException(ErrorCode.CREDIT_CARD_EXPIRED);

As each error has a unique code, you are prepared to map each error on the messages.properties file:

101 = The name is invalid
102 = Order not found
103 = Credit card is expired
104 = The informed value is too short

With this simple approach, you are already able to share all mapped and possible error codes of your application to anyone.

If you need to pass a parameter to the message, just create the exception and set the values on it:

SystemException ex = new SystemException(ErrorCode.ORDER_NOT_FOUND)
ex.set("number", "1234567");

No mistery on the properties:

102 = Order number {0} not found

When you need to deal with checked exceptions from third libraries or “legacy” code, the idea is to encapsulate the checked exception on the SystemException. Just choose the best error code to represent that condition and throw it. But don’t forget to log the error before, like:

try {
    // some third library trying to write/read a file
} catch (FileNotFoundException ex) {
    log.error("The file {} was not found", fileName, ex);
    throw new SystemException(ErrorCode.CONTRACT_NOT_FOUND);
}

The details about the code you can find on my Github repository. Some parts of my implementation are slightly different from what I showed on the text, but it’s just details that you can adjust. The original idea of this implementation came from this blog.

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