Re: annotation metadata proposal

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 31 Oct 2014 20:53:26 -0400

Message-ID:

<54542f09$0$294$14726298@news.sunsite.dk>

On 10/31/2014 12:06 AM, boxzou@gmail.com wrote:

1. Problem:
Suppose I wrote 2 classes summer.sports.Soccer and winter.sports.Hockey each in their own jar (soccer.jar and hockey.jar). Each class is annotation @Sport. Now at runtime, I want to find all classes annotated with @Sport.

Scanning all jars is kinda expensive.

The alternative is to have a properties file where you can list all such classes or better yet packages that contain those classes. Each jar file would have such a properties file.

But it is tedious to maintain such list.

Note I allow new sports jar added, I can not specify the packages using something like Spring framework's component:scan(packages) because I can not predict future.

I think tools can help.

2. Proposal:
     a) add an file in jar: META-INF/annotated-classes
     b) format: full.class.name:Ann1,Ann2, one class per line
     c) mvn plugin to generate META-INF/annotated-classes and package it in jar/war
     d) IDE: when building a project generate such entry and put in output folder (e.g. target/classes)
     e) provide library to read all META-INF/annotated-classes

What do you think?

That is practically the same as the properties file solution just with
automatic generation instead of manual maintenance.

But fundamentally I don't understand the approach.

You can have a file with a list of classes that are special.

Or you can add an annotation to classes that are special.

But I do not see the point in doing both.

If you drop adding the annotation to classes and instead just maintain
the list then it is only one manual change and you get the
functionality you want.

Arne