Fall back to the default charset when the request charset name is not a legal name

[17krishna8]

Charset.forName() throws IllegalCharsetNameException for a name that is not even a legal charset name, next to UnsupportedCharsetException for a legal but unknown one, and only the latter was caught in RequestUtils.getCharset().

The name comes from the character encoding of the servlet request, which a client influences through the charset parameter of the Content-Type header (whether such a name reaches the application differs between containers), so the value could surface as an unhandled runtime exception while the request charset is resolved.

Both exceptions are now handled the same way: the encoding is unknown and the default charset is used.

[reiern70]

Thanks, looks good. On master RequestUtils.getCharset() throws IllegalCharsetNameException for !!invalid!!; with the change it falls back to the default, as it already does for an unknown name.

Optional, same pattern: MultipartServletWebRequestImpl reads request.getCharacterEncoding() (line 151) and passes it to Charset.forName() (around lines 213 and 334) without catching either exception. Fine to cover it here, or leave it for a follow-up.

[17krishna8]

Thanks! I left the multipart part for a follow-up so this one can go in as is: #1677.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.96%. Comparing base (5cbd566) to head (95492d8).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1675   +/-   ##
=========================================
  Coverage     61.96%   61.96%           
- Complexity    11285    11286    +1     
=========================================
  Files          1250     1250           
  Lines         48437    48437           
  Branches       6796     6796           
=========================================
+ Hits          30014    30015    +1     
  Misses        15729    15729           
+ Partials       2694     2693    -1     

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