捕获意外异常是一种好习惯吗？

Question

I am writing a web application using Spring 3 framework. Consider a situation where I have N number of controllers. Each controller delegates the request to exposed services and gets the response and return to users.

I would like to know if there is a better to way catch unexpected runtime exceptions thrown out of the controller code. I do not want to write something like the following for each of my controller methods. Or is it the only way?

try {
     //call the service
} catch(ServiceException serviceEx) {
    //do process for know exception  
} catch(Exception ex) {
    //return generic error message.
}

I know that we can use Spring Exception resolver. But I do not want to show different error page when unexpected error happens. I want to show some generic error message on UI as part of my widget?

Edit:

I also don't want my users to see the exception stacktrace when trying to perform some operations.

Sundar

Answer 1

I think catching RuntimeException s is bad practice. Originally RuntimeException s where thought as inicators to programming errors (eg NullPointerException to indicate that a null check is missing). Whereas checked exceptions where meant to indicate errors that the program can recover from (eg FileNotFoundException ).

The problem today is that many frameworks use RuntimeException s where checked exceptions should be used. Therefore it is difficult to differentiate between cases where a program can handle the exception and where a programming error (bug) is encountered.

This is my personal view of this things for enterprise development. I know that most people mandate for dropping checked exceptions and handle everything as unchecked exception (as in Scala).

Answer 2

In my opinion you should only catch exceptions in your code from which you can recover. All other exceptions (checked or unchecked) should be caught by one über exceptionhandler which will log the exception and show the user some generic error page (possibly with an id that you can use to find what the exception was).

For example, in struts2 you would that this like so:

<global-exception-mappings>
    <exception-mapping exception="java.lang.Exception" result="unrecoverableException"/>
</global-exception-mappings>

I never use spring mvc but this article seems to give you the options for an über exceptionhandler:

http://doanduyhai.wordpress.com/2012/05/06/spring-mvc-part-v-exception-handling/

Answer 3

You can catch runtime unexpected exceptions using this approach.

  try {
  ...
  } catch ( Exception e ) {
  throw new RuntimeException("msg",e);
  }  

Answer 4

I think RuntimeException is designed for situations like breach of contract or some unrecoverable fault. Most of the time, you should just let the container or some outer infrastructure to handle it for you. Or you have to write a lot of redundant code to deal with them and it's kind of against the design philosophy of Spring.

In your case, may be you can leverage some filter or interceptor to catch those unexpected RuntimeException if you really need to transfer them to some other generic messages.