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https://issues.apache.org/jira/browse/IO-192?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Niall Pemberton updated IO-192:
-------------------------------
Attachment: IO-192-tagged-stream-changes.patch
Hi Jukka,
I like the concept but have some comments/suggestions on the implementation of
this.
1) Its a useful feature to be able to handle exceptions - not just in this
use-case for tagging, but generally so IMO it would be good to move the
exception handling into the Proxy stream implementations. We could provide a
protected handleException(IOException) method that by default just re-throws
the exception to keep compatibility, but a allows people to override for their
own custom exception handling.
2) Exceptions are Serializable and many stream implementations are not so I
have some concern about holding a reference to the stream in the
TaggedIOException. Also this could cause references to the stream being held
longer than previously by the application and prevent/delay garbage collection.
An alternative could be to store the identity hash code of the tag object
instead.
3) The current solution requires users to reference the concrete tagged stream
implementations. While this is OK in your simple example within a single method
its not good practice generally and will either encourage people to pollute
their API with these tagged streams or require additional casting. I suggest we
move the code for handling these streams into IOUtils - which also makes it
more generic and available to re-use for other tagging requirements, not just
by the throwing stream.
{code}
InputStream input = ...;
OutputStream output = ...;
OutputStream proxy = new TaggedOutputStream(output);
try {
IOUtils.copy(input, proxy);
} catch (IOException e) {
if (IOUtils.isTaggedBy(e, proxy)) {
...
}
}
{code}
I am attaching a patch with my suggestions
> Tagged input and output streams
> -------------------------------
>
> Key: IO-192
> URL: https://issues.apache.org/jira/browse/IO-192
> Project: Commons IO
> Issue Type: New Feature
> Components: Streams/Writers
> Reporter: Jukka Zitting
> Assignee: Jukka Zitting
> Priority: Minor
> Fix For: 1.5
>
> Attachments: IO-192-tagged-stream-changes.patch, IO-192.patch
>
>
> I'd like to introduce two new proxy streams, TaggedInputStream and
> TaggedOutputStream, that tag all exceptions thrown by the proxied streams.
> The goal is to make it easier to detect the source of an IOException when
> you're dealing with multiple different streams. For example:
> {code}
> InputStream input = ...;
> OutputStream output = ...;
> TaggedOutputStream proxy = new TaggedOutputStream(output);
> try {
> IOUtils.copy(input, proxy);
> } catch (IOException e) {
> if (proxy.isTagged(e)) {
> // Could not write to the output stream
> // Perhaps we can handle that error somehow (retry, cancel?)
> e.initCause(); // gives the original exception from the proxied stream
> } else {
> // Could not read from the input stream, nothing we can do
> throw e;
> }
> }
> {code}
> I'm working on a patch to implement such a feature.
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