java - when and how will ImageIO.write throw nullpointerexception? -

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in

imageio.write(renderedimage,string,file)

method, imageoutputstream created through

stream = createimageoutputstream(output);.

in createimageoutputstream runtime exception caught , returns null catch block.

try {     iter = theregistry.getserviceproviders(imageoutputstreamspi.class,true);         } catch (illegalargumentexception e) {             return null;         }

can me understand:

  1. what reason behind catching runtime exception here?(unless crappy coding)
  2. on condition, code throw illegal argument exception? (i dont see reason throw)

please help.

it case of code has evolved on time , no 1 cared clean up, or implementers of imageio relied on contract of serviceregistry, rather implementation details of it. in current implementation of imageio , serviceregistry don't see how ever happen.

the thing can see it, potentially change implementation of iioregistry or serviceregistry lazy loading of categories example, or perhaps flush out categories no service providers (spi) present. contracts of methods not break, , imageio class still work does.

now, question in question, answer should never throw nullpointerexception. *

if want to, stream null, de-registering spi file (fileimageoutputstreamspi). then, well-behaved imagewriter should throw illegalstateexception indicating output has not been set, not nullpointerexception (of course, programming errors cause npes in other places, not normal flow).

update:

*) op himself pointed out in linked answer, throwing of nullpointerexception can indeed happen if pass file object pointing non-existing path. happens because fileimageoutputstreamspi "swallows" ioexception caused randomaccessfile constructor (it print stacktrace standard out), , returns null. in opinion, breaks contract in more severe way letting ioexception bubble up, or wrapping in illegalargumentexception original exception cause , explanatory message. consider filing bug report, if doesn't exist 1 issue.


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