Support for a convention and flexible @Sources configuration: @AutoSources

[rrialq]

It should be interesting adding a flexible convention feature about @Sources to the library. This would allow a loosely coupled configuration mechanism, with the following additional benefits:

• It is not longer necessery to know the rules in design time about importing properties.
• Configuration is delegated at a properties file. If you change the rules about importing properties files Owner should reload them (when it is possible).
• Code is more simply.
• Administration is more simply: you change the properties of the host and all of configurations of all of your servers are automatically reloaded to reflect the new changes.

When you develop software following guidelines about configuration maybe you need a way to configure a flexible way to "wrap" the @Sources definition, with a simple set of rules, something like a @AutoSources annotation, which may be combined with **@Sources** annotation.

For example, the rules should be the following, from lower to higher priority:

• classpath:${className}: a properties file called (this should be normally an embedded in same jar as your application.
• file:${configurationPath}/${className}: a properties file in the folder specified by owner.configuration.path.
• file:${configurationPath}/${serverName}.server.properties: a properties file for overriding configurations only on the server which id is serverName.
• file:${configurationPath}/${hostName}.host.properties: a properties file for overriding configurations on the host where all my servers are running.

Imagine now that we have a way to support automatically this kind of configurations in all of our applications without writing specific @Sources annotation, so we can get the following code equivalence:

@Sources( {
    "file:${configurationPath}/global.properties",
    "file:${configurationPath}/myHostName.host.properties",
    "file:${configurationPath}/myServerName.server.properties",
    "file:${configurationPath}/org/aeonbits/owner/demo.properties",
    "classpath:org/aeonbits/owner/demo.properties"
})
public interface Demo extends Config {
...
}

only writing the following code:

@AutoSources
public interface Demo extends Config {
...
}

or better yet:

@AutoSources( "myid" )
public interface Demo extends Config {
...
}

So you can write a few properties in a file in a way similar to:

# Global rules for managing all configurations
# Prepend to uris
global.sources.prepend=file:${configurationPath}/global.properties,\
file:${configurationPath}/myhost.host.properties,\
file:${configurationPath}/myserver.server.properties,\
file:${configurationPath}/myinstance.instance.properties
# Append to uris
global.sources.append=file:${configurationPath}/global.append.properties
#Exclude applying this rule for classes which name matches following regular expression:
global.sources.exclude=org\.aeonbits\.owner\.demo24

#Rules for envolving the configurations annotated with @AutoSources( "myid" )
myid.sources.prepend=file:${user.home}/autosource/myid.properties
#Set to true if you want to disable the autosources on myid
myid.sources.disable=false

I am working on this feature, and when I finish my tests I will do a pull to propose add this feature into Owner.

[lviggiano]

Hi.

I'll review your message above more in detail later, but my first thoughts are that when you don't specify the @Sources annotation, owner already has some default behavior (loading from the classpath a properties file with same name and package as the driving interface). So, maybe, it would be better to extend the default paths loading, instead of creating a new @AutoSource annotation, that checks if some system properties are specified.

Also I don't see much of advantage to have an external properties file to define what at the moment is specified by the @sources annotation.

I would go for an extension of the default loading sources instead of making it more complex and difficult to understand for the end users.

Eventually, if the end user needs a more complex strategy to identify from where to load the properties files, maybe we can let him to specify a @SourcesLocatorClass(MySourceLocator) and have the end user implement the algorithm to identify a single URI or a list of URI to load the properties.

At the moment, new features added are lacking documentation (and this means that they are incomplete for a release), and unfortunately I don't have much time to dedicate to this project.

Also, I think it is important to keep things simple.