Question

How can this be? Looks like plain as daylight an exception from a third party library is skipping my catch block. Not sure where to begin troubleshooting this. It’s either me being really stupid, or me not understanding something subtle about exceptions and Java.

My console:

Exception: org.apache.james.mime4j.io.MaxLineLimitException: Maximum line length limit exceeded; stack: org.apache.james.mime4j.stream.MimeEntity.readRawField(MimeEntity.java:242);
org.apache.james.mime4j.stream.MimeEntity.nextField(MimeEntity.java:258);
org.apache.james.mime4j.stream.MimeEntity.advance(MimeEntity.java:296);
org.apache.james.mime4j.stream.MimeTokenStream.next(MimeTokenStream.java:360);
me.unroll.scanner.Scanner.<init>(Scanner.java:206);
me.unroll.scanner.ScannerThread.run(ScannerThread.java:205);
java.lang.Thread.run(Thread.java:722)

Problem is my code looks like this:

try {  
//...
 for(EntityState token = messageStream.getState();
    token != EntityState.T_END_OF_STREAM;
    token = messageStream.next()) {  //this is Scanner.java:206
//...
catch(ScanComplete exc) { }
catch(MaxLineLimitException exc) { //line 282, matches "try" above
    debug("Am I getting caught?"); //no, it's not

I’m more

Answer 1

You’re attempting to catch the wrong exception type.

The signature for MimeTokenStream.next() says it can throw MimeException, which you are not catching. (BTW if you are wondering why an exception isn’t being caught, you can try catching Exception and logging the exception type to see what is actually being thrown.)

Now, if you look at the source code for the actual source of the exception, line 242 of MimeEntity.readRawField, you’ll see:

241        } catch (MaxLineLimitException e) {
242            throw new MimeException(e);
243        }

So even though the console message says MaxLineLimitException, the actual exception being thrown by that method is a MimeException. Try catching MimeException in your code instead of MaxLineLimitException, but beware that MimeTokenStream.next() can probably throw MimeException for other reasons besides the one you’ve encountered.