1) With that rex, you should only get the first one. (max_match defaults to 1) This is assuming that the rex contains a field name in angle brackets <>. Please mark your code - either with the 101 010 button or the grave accent (to the left of the 1 on a standard US keyboard) before and after it to prevent the interface from obeying or stripping out things that look like HTML formatting commands. For large pieces of code, you can also just make sure there are at least four spaces at the beginning of each line.
|rex field=_raw "\s(?<myExcp>(java|javax).\w+.\w+Exception)"
2) If the sourcetype is set to extract KV, you will get all of them.
