109 lines
4.3 KiB
Markdown
109 lines
4.3 KiB
Markdown
---
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parent: Decision Records
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nav_order: 14
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---
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# Separate URL creation to enable proper logging
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## Context and Problem Statement
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Fetchers are failing.
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The reason why they are failing needs to be investigated.
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* Claim 1: Knowing the URL which was used to query the fetcher eases debugging
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* Claim 2: Somehow logging the URL eases debugging (instead of showing it in the debugger only)
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How to properly log the URL used for fetching?
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## Decision Drivers
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* Code should be easy to read
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* 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>)
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## Considered Options
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* Separate URL creation
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* Create URL when logging the URL
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* Include URL creation as statement before the stream creation in the try-with-resources block
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## Decision Outcome
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Chosen option: "Separate URL creation", because comes out best \(see below\).
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## Pros and Cons of the Options
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### Separate URL creation
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```java
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URL urlForQuery;
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try {
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urlForQuery = getURLForQuery(query);
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} catch (URISyntaxException | MalformedURLException | FetcherException e) {
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throw new FetcherException(String.format("Search URI %s is malformed", query), e);
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}
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try (InputStream stream = getUrlDownload(complexQueryURL).asInputStream()) {
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...
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} catch (IOException e) {
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throw new FetcherException("A network error occurred while fetching from " + urlForQuery.toString(), e);
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} catch (ParseException e) {
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throw new FetcherException("An internal parser error occurred while fetching from " + urlForQuery.toString(), e);
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}
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```
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* Good, because exceptions thrown at method are directly caught
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* Good, because exceptions in different statements belong to different catch blocks
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* Good, because code to determine URL is written once
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* OK, because "Java by Comparison" does not state anything about it
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* Bad, because multiple try/catch statements are required
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* Bad, because this style seems to be uncommon to Java coders
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### Create URL when logging the URL
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The "logging" is done when throwing the exception.
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Example code:
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```java
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try (InputStream stream = getUrlDownload(getURLForQuery(query)).asInputStream()) {
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...
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} catch (URISyntaxException | MalformedURLException | FetcherException e) {
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throw new FetcherException(String.format("Search URI %s is malformed", query), e);
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} catch (IOException e) {
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try {
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throw new FetcherException("A network error occurred while fetching from " + getURLForQuery(query), e);
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} catch (URISyntaxException | MalformedURLException uriSyntaxException) {
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// does not happen
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throw new FetcherException("A network error occurred", e);
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}
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} catch (ParseException e) {
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try {
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throw new FetcherException("An internal parser error occurred while fetching from " + getURLForQuery(query), e);
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} catch (URISyntaxException | MalformedURLException uriSyntaxException) {
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// does not happen
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throw new FetcherException("An internal parser error occurred", e);
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}
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}
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```
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* Good, because code inside the `try` statement stays the same
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* OK, because "Java by Comparison" does not state anything about it
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* Bad, because an additional try/catch-block is added to each catch statement
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* 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.
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### Include URL creation as statement before the stream creation in the try-with-resources block
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```java
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try (URL urlForQuery = getURLForQuery(query); InputStream stream = urlForQuery.asInputStream()) {
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...
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} catch (URISyntaxException | MalformedURLException | FetcherException e) {
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throw new FetcherException(String.format("Search URI %s is malformed", query), e);
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} catch (IOException e) {
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throw new FetcherException("A network error occurred while fetching from " + urlForQuery.toString(), e);
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} catch (ParseException e) {
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throw new FetcherException("An internal parser error occurred while fetching from " + urlForQuery.toString(), e);
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}
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```
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* Good, because the single try/catch-block can be kept
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* Good, because logical flow is kept
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* Bad, because does not compile (because URL is not an `AutoClosable`)
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