This repository houses the logic for generating the javadoc content served from javadoc.scijava.org.

TL;DR: What is generated

Actual javadoc for each component. E.g. /org.scijava/scijava-common/2.87.1/. Analogous to javadoc.io, but also supports artifacts deployed to maven.scijava.org. And javadoc of supported components is unpacked in advance, not on the fly on demand.
Unioned index of all managed components for a particular BOM. E.g. /org.scijava/pom-scijava/31.1.0/. Useful for passing as a link to the javadoc tool, or when you want to access the javadoc for a library corresponding to a particular BOM version. Actual class and package javadoc is referenced via 301 redirects to the correct component. For example, the path:
```
/org.scijava/pom-scijava/31.1.0/net/imglib2/img/Img.html
```
redirects to:
```
/net.imglib2/imglib2/5.12.0/net/imglib2/img/Img.html
```
Because the net.imglib2.img.Img class is part of net.imglib2:imglib2:5.12.0, one of the BOM's managed components.
Toplevel index of available javadoc.

Background and rationale

The generated content is designed around the idea of a Bill of Materials (BOM), which provides a list of managed components at particular versions that are tested and working together. By importing the BOM into your build, you can then depend on any combination of the managed components without explicitly declaring their versions, and the versions will be inferred from the BOM.

Now suppose you are developing a Java library L that depends on several managed components: A, B, C, D, etc. One of the steps when building L is to generate its javadoc, package it into a JAR file with classifier javadoc, and deploy the resulting L-x.y.z-javadoc.jar artifact to a remote Maven repository.

These javadoc artifacts are useful for IDEs to browse javadoc on demand from within the user interface. But there are two major drawbacks:

Humans cannot read the javadoc directly in a web browser.
The javadoc tool cannot consume them as links when generating downstream javadoc, so your library L will not have hyperlinks to classes from dependencies A, B, C, D, etc.

For projects deployed to Maven Central, one solution is javadoc.io, which offers on-demand browsing of any project that publishes javadoc classifier artifacts as described above. Links to javadoc.io-hosted javadoc (e.g. SciJava Common v2.87.1) can be passed to the javadoc tool as links, and the javadoc for your library L will then have hyperlinks to the classes of dependencies A, B, C, D, etc., for which javadoc.io links were provided.

There are still challenges, however:

For each link given to the javadoc tool, its element-list (package-list in older versions of Java) index must be fetched. Unfortunately, this step is slow, scaling linearly by the number of links given. For projects with many dependencies, each with its own javadoc.io link, this can bloat javadoc generation time by many minutes. In an empirical test, building javadoc for a small project with no links took 11 seconds, with 37 links took 48 seconds, and with 231 links took 215 seconds.
The javadoc.io service does not support javadoc artifacts published to Maven repositories other than Maven Central. So projects published to maven.scijava.org, for example, cannot be browsed there. And as far as I know, the server-side javadoc.io code is not open source, so configuring javadoc.scijava.org to work analogously, but for maven.scijava.org instead of Maven Central, requires coding our own solution (i.e., this repository).

How this repository helps

The wrangle.py script generates a combined javadoc target for a BOM, unioning the element-list/package-list index so that it can be passed to the javadoc tool as a single link target, resulting in fast javadoc build times, with permanent reproducible links embedded in the resultant javadoc.

The script also unpacks the actual javadoc for each managed component.

The combined javadoc target, rather than recapitulating the HTML for every class of every component, instead uses 301 redirects via an Apache .htaccess file, which point at the unmodified unpacked javadoc for that component.

This approach has several advantages:

The javadoc tool has a single reproducible link target, so new javadoc builds more quickly, with classes from dependencies linked with permalinks.
Every available javadoc for every component managed by every version of pom-scijava is accessible from a canonical location, with stable links.
Old javadoc using version-agnostic (and therefore irreproducible) links is adjusted during unpacking to use stable links instead—e.g., /SciJava/org/scijava/Context.html → /org.scijava/pom-scijava/30.0.0/org/scijava/Context.html which then redirects to org.scijava/scijava-common/2.85.0/org/scijava/Context.html.

The various version-agnostic prefixes from the prior incarnation of the javadoc.scijava.org website now redirect to the latest pom-scijava javadoc prefix—e.g., /SciJava/ → /org.scijava/pom-scijava/latest/ → org.scijava/pom-scijava/31.1.0, with the latest path updating over time to always redirect to the newest BOM version hosted on the site.