Hello. I hope to open a discussion about the import order in Java code.
As Nikolay stated recently[^1], Kafka uses a relatively strict code style
for Java code. However, it misses any rule on import order. For this
reason, the code formatting settings of every local dev environment are
different from person to person, resulting in the countless meaningless
import order changes in the PR.
For example, in `NamedCache.java` in the streams module, the `java.*`
imports are split into two chunks, embracing the other imports between
them. So, I propose to define an import order to prevent these kinds of
cases in the future.
To define the import order, we have to regard the following three
orthogonal issues beforehand:
a. How to group the type imports?
b. Whether to sort the imports alphabetically?
c. Where to place static imports: above the type imports, or below them.
Since b and c seem relatively straightforward (sort the imports
alphabetically and place the static imports below the type imports), I hope
to focus the available alternatives on the problem a.
I evaluated the following alternatives and checked how many files are get
effected for each case. (based on commit 1457cc652) And here are the
results:
*1. kafka, org.apache.kafka, *, javax, java (5 groups): 1222 files.*
```
<module name="ImportOrder">
<property name="groups"
value="kafka,/^org\.apache\.kafka.*$/,*,javax,java"/>
<property name="ordered" value="true"/>
<property name="separated" value="true"/>
<property name="option" value="bottom"/>
<property name="sortStaticImportsAlphabetically" value="true"/>
</module>
```
*2. (kafka|org.apache.kafka), *, javax? (3 groups): 968 files.*
```
<module name="ImportOrder">
<property name="groups" value="(kafka|org\.apache\.kafka),*,javax?"/>
<property name="ordered" value="true"/>
<property name="separated" value="true"/>
<property name="option" value="bottom"/>
<property name="sortStaticImportsAlphabetically" value="true"/>
</module>
```
*3. (kafka|org.apache.kafka), *, javax, java (4 groups): 533 files.*
```
<module name="ImportOrder">
<property name="groups"
value="(kafka|org\.apache\.kafka),*,javax,java"/>
<property name="ordered" value="true"/>
<property name="separated" value="true"/>
<property name="option" value="bottom"/>
<property name="sortStaticImportsAlphabetically" value="true"/>
</module>
```
*4. *, javax? (2 groups): 707 files.*
```
<module name="ImportOrder">
<property name="groups" value="*,javax?"/>
<property name="ordered" value="true"/>
<property name="separated" value="true"/>
<property name="option" value="bottom"/>
<property name="sortStaticImportsAlphabetically" value="true"/>
</module>
```
*5. javax?, * (2 groups): 1822 files.*
```
<module name="ImportOrder">
<property name="groups" value="javax?,*"/>
<property name="ordered" value="true"/>
<property name="separated" value="true"/>
<property name="option" value="bottom"/>
<property name="sortStaticImportsAlphabetically" value="true"/>
</module>
```
*6. java, javax, * (3 groups): 1809 files.*
```
<module name="ImportOrder">
<property name="groups" value="java,javax,*"/>
<property name="ordered" value="true"/>
<property name="separated" value="true"/>
<property name="option" value="bottom"/>
<property name="sortStaticImportsAlphabetically" value="true"/>
</module>
```
I hope to get some feedback on this issue here.
For the WIP PR, please refer here: https://github.com/apache/kafka/pull/8404
Best,
Dongjin
[^1]:
https://lists.apache.org/thread.html/r2bbee24b8a459842a0fc840c6e40958e7158d29f3f2d6c0d223be80b%40%3Cdev.kafka.apache.org%3E
[^2]:
https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/state/internals/NamedCache.java
--
*Dongjin Lee*
*A hitchhiker in the mathematical world.*
*github: <http://goog_969573159/>github.com/dongjinleekr
<https://github.com/dongjinleekr>keybase: https://keybase.io/dongjinleekr
<https://keybase.io/dongjinleekr>linkedin: kr.linkedin.com/in/dongjinleekr
<https://kr.linkedin.com/in/dongjinleekr>speakerdeck: speakerdeck.com/dongjin
<https://speakerdeck.com/dongjin>*
