enums - Best way to define error codes/strings in Java?

Question

I am writing a web service in Java, and I am trying to figure out the best way to define error codes and their associated error strings. I need to have a numerical error code and an error string grouped together. Both the error code and error string will be sent to the client accessing the web service. For example, when a SQLException occurs, I might want to do the following:

// Example: errorCode = 1, 
//          errorString = "There was a problem accessing the database."
throw new SomeWebServiceException(errorCode, errorString);

The client program might be shown the message:

"Error #1 has occured: There was a problem accessing the database."

My first thought was to used an Enum of the error codes and override the toString methods to return the error strings. Here is what I came up with:

public enum Errors {
  DATABASE {
    @Override
    public String toString() {
      return "A database error has occured.";
    }
  },

  DUPLICATE_USER {
    @Override
    public String toString() {
      return "This user already exists.";
    }
  },

  // more errors follow
}

My question is: Is there a better way to do this? I would prefer an solution in code, rather than reading from an external file. I am using Javadoc for this project, and being able to document the error codes in-line and have them automatically update in the documentation would be helpful.

Answer 1

Well there's certainly a better implementation of the enum solution (which is generally quite nice):

public enum Error {
  DATABASE(0, "A database error has occurred."),
  DUPLICATE_USER(1, "This user already exists.");

  private final int code;
  private final String description;

  private Error(int code, String description) {
    this.code = code;
    this.description = description;
  }

  public String getDescription() {
     return description;
  }

  public int getCode() {
     return code;
  }

  @Override
  public String toString() {
    return code + ": " + description;
  }
}

You may want to override toString() to just return the description instead - not sure. Anyway, the main point is that you don't need to override separately for each error code. Also note that I've explicitly specified the code instead of using the ordinal value - this makes it easier to change the order and add/remove errors later.

Don't forget that this isn't internationalised at all - but unless your web service client sends you a locale description, you can't easily internationalise it yourself anyway. At least they'll have the error code to use for i18n at the client side...