Question

At the moment I am developing a website while using the Playframework2. I am just a beginner in programming. I read some books about exceptions but now in the real world , exception handling is really strange.

To be honest I don’t really care what exceptions are thrown I handle all exceptions the same way.
return badrequest(); . I only use exceptions for logging.

try{
...
}
catch(Exeption e){
//log
return badrequest();
}

But this is so much boilerplate and it’s really annoying to write, because every method throws the same exceptions.

Any tips , hints or resources that you could give me?

edit:

An example would be my “global” config file. Because I need to connect to the db every time I thought i could write a singleton for this problem.

private Datastore connect() throws UnknownHostException, MongoException,
            DbAuthException {

        Mongo m = new Mongo(dbUrl, dbPort);
        Datastore ds = new Morphia().createDatastore(m, dbName);
        boolean con = ds.getDB().authenticate(username, password.toCharArray());
        if (!con)
            throw new DbAuthException();
        return ds;
    }

This also results in a try and catch every time I want to connect to the db. My problem is I don’t think I can handle them diffidently.

A code example :

public static Result addComment(String title) {
        try {

            Datastore ds = DatabaseConnect.getInstance().getDatastore();
            Form<Comment> filledForm = commentForm.bindFromRequest();
            Comment userComment = filledForm.get();
            userComment.setUsername(Util.getUsernameFromSession(ctx()));
            User.increasePointsBy(ctx(), 1);
            UserGuides.addComment(title, userComment);
        } catch (Exception e) {
            return badRequest();
        }
        return redirect(routes.Guides.blank());
    }

In this case I was to lazy to write the same try and catch over and over again, and this is duplicated code.

Maybe there is a book that explains how to design a big application with exception handling?

Answer 1

When you invoke a method, you do not necessarily have to catch the exceptions right there. You can let your callers handle them (declaring a throws clause if it is a checked exception). In fact, the ability to pass them on to the callers without any additional work is the distinguishing feature of exceptions.

My team has adopted the following coding standard: We throw checked exceptions for those rare cases when we want to recover from a failure, and unchecked exceptions for anything else. There is only a single catch block for the unchecked exceptions in a method so high in the call stack that all requests pass through it (for instance in a ServletFilter). This catch block logs the exception, and forwards the user to the “Sorry, this shouldn’t have happened” page.