Separate URL creation to enable proper logging

Context and Problem Statement

Fetchers are failing. The reason why they are failing needs to be investigated.

• Claim 1: Knowing the URL which was used to query the fetcher eases debugging
• Claim 2: Somehow logging the URL eases debugging (instead of showing it in the debugger only)

How to properly log the URL used for fetching?

Decision Drivers

• Code should be easy to read
• Include URL in the exception instead of logging in case an exception is thrown already (see https://howtodoinjava.com/best-practices/java-exception-handling-best-practices/#6)

Considered Options

• Separate URL creation
• Create URL when logging the URL
• Include URL creation as statement before the stream creation in the try-with-resources block

Decision Outcome

Chosen option: “Separate URL creation”, because comes out best (see below).

Pros and Cons of the Options

Separate URL creation

 URL urlForQuery; try { urlForQuery = getURLForQuery(query); } catch (URISyntaxException | MalformedURLException | FetcherException e) { throw new FetcherException(String.format("Search URI %s is malformed", query), e); } try (InputStream stream = getUrlDownload(complexQueryURL).asInputStream()) { ... } catch (IOException e) { throw new FetcherException("A network error occurred while fetching from " + urlForQuery.toString(), e); } catch (ParseException e) { throw new FetcherException("An internal parser error occurred while fetching from " + urlForQuery.toString(), e); } 

• Good, because exceptions thrown at method are directly caught
• Good, because exceptions in different statements belong to different catch blocks
• Good, because code to determine URL is written once
• OK, because “Java by Comparison” does not state anything about it
• Bad, because multiple try/catch statements are required
• Bad, because this style seems to be uncommon to Java coders

Create URL when logging the URL

The “logging” is done when throwing the exception.

Example code:

 try (InputStream stream = getUrlDownload(getURLForQuery(query)).asInputStream()) { ... } catch (URISyntaxException | MalformedURLException | FetcherException e) { throw new FetcherException(String.format("Search URI %s is malformed", query), e); } catch (IOException e) { try { throw new FetcherException("A network error occurred while fetching from " + getURLForQuery(query), e); } catch (URISyntaxException | MalformedURLException uriSyntaxException) { // does not happen throw new FetcherException("A network error occurred", e); } } catch (ParseException e) { try { throw new FetcherException("An internal parser error occurred while fetching from " + getURLForQuery(query), e); } catch (URISyntaxException | MalformedURLException uriSyntaxException) { // does not happen throw new FetcherException("An internal parser error occurred", e); } } 

• Good, because code inside the try statement stays the same
• OK, because “Java by Comparison” does not state anything about it
• Bad, because an additional try/catch-block is added to each catch statement
• Bad, because needs a throw statement in the URISyntaxException catch block (even though at this point the exception cannot be thrown), because Java otherwise misses a return statement.

Include URL creation as statement before the stream creation in the try-with-resources block

 try (URL urlForQuery = getURLForQuery(query); InputStream stream = urlForQuery.asInputStream()) { ... } catch (URISyntaxException | MalformedURLException | FetcherException e) { throw new FetcherException(String.format("Search URI %s is malformed", query), e); } catch (IOException e) { throw new FetcherException("A network error occurred while fetching from " + urlForQuery.toString(), e); } catch (ParseException e) { throw new FetcherException("An internal parser error occurred while fetching from " + urlForQuery.toString(), e); } 

• Good, because the single try/catch-block can be kept
• Good, because logical flow is kept
• Bad, because does not compile (because URL is not an AutoClosable)