Add "Setting up an AspectJ development environment" guide

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

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+# Setting up an AspectJ development environment
+
+_by Alexander Kriegisch, 2021-08-05_
+
+AspectJ, being an Eclipse project, can of course be used in the Eclipse IDE for Java developers, if you also install the
+AspectJ Development Tools (AJDT). IntelliJ IDEA also offers AspectJ and Spring AOP support. Regarding build tools, there
+are AspectJ plugins for Maven, Gradle and Ant.
+
+Of course, you can use and other IDE and build tool or simply use your trusted text editor of choice and compile using
+the AspectJ Compiler _ajc_ from the command line.
+
+Please refer to the [AspectJ Development Environment Guide](https://www.eclipse.org/aspectj/doc/next/devguide/printable.html)
+for more details about on-board AspectJ tools, such as _ajc_ (compiler), _ajdoc_ (aspect-enriched Javadoc), _aj_
+(load-time weaving helper), AspectJ Browser (simple visualisation tool for cross-cutting aspect structure) as well as
+basic information about load-time weaving configuration and the built-in Ant task for AspectJ.
+
+## IDE support
+
+We are going to focus on the two IDEs the author of this document is acquainted with, Eclipse and IntelliJ IDEA. That
+does not mean that others such as NetBeans or the increasingly popular editor-on-steroids Visual Studio Code might not
+also be excellent choices, but I simply do not know them, sorry.
+
+### Eclipse
+
+If you install [AspectJ Development Tools (AJDT)](https://www.eclipse.org/ajdt/), you can use AspectJ in the Eclipse
+Java IDE. For the last few years, AJDT has rather been kept alive than actively developed, but still it works nicely for
+the usual tasks, such as writing aspects in both native and annotation-style syntax, viewing cross-references between
+aspects and Java code, applying all sorts of weaving strategies (compile-time weaving, post-compile binary weaving,
+load-time weaving) and with an additional m2e (Maven to Eclipse) connector also for importing and refreshing from
+projects using AspectJ Maven Plugin.
+
+#### AspectJ Development Tools (AJDT)
+
+Use an update sites corresponding to your Eclipse version (minimal version listed):
+* Eclipse 2021-03 (4.19): https://aspectj.dev/eclipse/ajdt/419
+* Eclipse 2018-12 (4.10): https://download.eclipse.org/tools/ajdt/410/dev/update
+* For older versions, please refer to https://www.eclipse.org/ajdt/downloads (page was not updated in a long time,
+  and I have no write access).
+
+#### Maven to Eclipse (m2e) connector
+
+The connector between AspectJ Maven Plugin and AJDT has not been maintained by the AspectJ team for some years, but
+there is a fairly up-to-date [fork by Miika Vesti (joker1)](https://github.com/joker1/m2eclipse-ajdt) with the following
+update sites:
+  * Eclipse 2020-12 (4.18): https://repo.t5.fi/public/eclipse/m2eclipse-ajdt/eclipse-2020-12/
+  * Eclipse 2019-06 (4.12): https://repo.t5.fi/public/eclipse/m2eclipse-ajdt/eclipse-2019-06/
+
+### IntelliJ IDEA
+
+IDEA is a commercial IDE by JetBrains, which also has a free Community Edition. The author of this guide uses a
+complementary Ultimate Edition provided by JetBrains (thank you!), because he is an active open source developer (ask
+them if you are eligible, too). If you want to use the Ultimate Edition for commercial purposes, however, of course you
+need to buy it. According to [this resource](https://www.jetbrains.com/help/idea/aspectj.html), the AspectJ plugin is
+for the Ultimate Edition only, so probably the plugin is not going to work in the Community Edition. But if you are
+using AspectJ in your daytime job, probably you use the Ultimate Edition anyway.
+
+Make sure that the following plugins are active:
+  * AOP Pointcut Language (bundled): basic AspectJ and Spring AOP pointcut syntax support (annotation style)
+  * AspectJ (marketplace, author JetBrains): native AspectJ support
+
+If the Maven support bundled into IntelliJ IDEA is active as well, Maven projects using the AspectJ Maven Plugin will
+also be imported correctly. I never tested with any of the Gradle plugins or the AspectJ Ant task because I am a Maven
+user, so please try for yourself if those combinations are supported.
+
+## Build tools
+
+### Maven
+
+If you want to build your AspectJ projects with Maven, use [AspectJ Maven Plugin](https://github.com/dev-aspectj/aspectj-maven-plugin)
+by AspectJ.dev, artifact ID `dev.aspectj:aspectj-maven-plugin`. It is a fork of the original plugin by MojoHaus, which
+was inactive for 3.5 years and only recently (2021-07-30) had a new release. Because the AspectJ.dev version (maintained
+by AspectJ contributor Alexander Kriegisch) has more features, we recommend using it instead of the original for
+original's sake.
+
+### Gradle
+
+In contrast to Maven, there is no de-facto standard build plugin for Gradle, but a bunch of more or less well-maintained
+plugins with a more or less complete feature set. I am not a Gradle user, but when answering related questions on
+StackOverflow, I got the impression that [Freefair by Lars Grefer](https://docs.freefair.io/gradle-plugins/current/reference/)
+is the one I want to recomment because of its good documentation, active development and feature set. It could well be
+or become for the Gradle ecosystem what AspectJ Maven is for the Maven one. At the time of writing this, the most recent
+milestone is [6.1.0-m3](https://docs.freefair.io/gradle-plugins/6.1.0-m3/reference/). 
+
+### Ant
+
+As mentioned in the introduction, AspectJ features its own Ant task, which is described in
+[this chapter](https://www.eclipse.org/aspectj/doc/next/devguide/printable.html#antTasks) of the Development Environment
+Guide.
+
+## Biased recommendation
+
+Feel free to be skeptical, because the author has both IDE and build tool biases, but I am recommending Maven as a build
+tool, AspectJ Maven as a build plugin and then either of Eclipse or IDEA as integrated development environments (IDEs).
+Why? Because Maven + (Eclipse or IDEA) probably has the most complete tooling and best end-to-end user experience for
+AspectJ developers. Because I am also by far the most active AspectJ and Spring AOP supporter on StackOverflow, you also
+have better chances to receive spot-on answers than if e.g. you ask why your Ant or Gradle build does not work so nicely
+in NetBeans or VS Code. But by all means, please do choose whichever combination of tools is the prescribed standard in
+your work environment or simply your personal pereference. I believe that diversity is good. 🙂