Chaining exceptions

[Andrei Alexandrescu]

Jesse Phillips wrote:
> On Wed, 18 Nov 2009 15:24:11 -0800, Andrei Alexandrescu wrote:
> 
>> Consider:
>>
>> void fun() {
>>     try {
>>        throw new Exception("a");
>>     } finally {
>>        throw new Exception("b");
>>     }
>> }
>>
>> Currently this function would unceremoniously terminate the program. I
>> think it shouldn't. What should happen is that the "a" exception should
>> be propagated unabated, and the "b" exception should be appended to it.
>> The Exception class should have a property "next" that returns a
>> reference to the next exception thrown (in this case "b"), effectively
>> establishing an arbitrarily long singly-linked list of exceptions.
>>
>> A friend told me that that's what Java does, with the difference that
>> the last exception thrown takes over, so the chain comes reversed. I
>> strongly believe "a" is the main exception and "b" is a contingent
>> exception, so we shouldn't do what Java does. But Java must have some
>> good reason to go the other way.
>>
>> Please chime in with (a) a confirmation/infirmation of Java's mechanism
>> above; (b) links to motivations for Java's approach, (c) any comments
>> about all of the above.
>>
>>
>> Thanks,
>>
>> Andrei
> 
> Best as I can tell, the Java compiler doesn't do the chaining 
> automatically. It is up to the one throwing the exception to make the 
> chain. The exception class just provides a specification that requires 
> all exceptions to support chaining. This explains why it is not the root 
> cause that is at the head of the chain.
> 
> try {
>      stmt.executeUpdate(sql);
> } catch (SQLException ex) {
>    throw new
>    EmployeeLookupException(
>    "Query failure",ex); // ex is passed to the constructor of the class
> } 
> 
> Example from: http://java.sys-con.com/node/36579
> 
> http://www.developer.com/tech/article.php/1431531/Chained-Exceptions-in-
> Java.htm

Thanks! Question - is there a way to fetch the current Throwable from 
within a finally clause?

Andrei