Gets rid of unwanted duplications in configuration Maps and allows configurations to inherit key-value pairs from other configurations, creating a transparent code with less duplications.
Every server needs some configuration, mostly it is stored in some Map. In many cases, parts of the configuration are dependent on each other (e.g. some Sockets use the same host as server, maybe some url is constructed from a host and port in other part of the config), and so there may be many duplications. Now imagine you have more modes (developer mode, testing mode, live mode ..) and each one of them needs a configuration of course - many parts of these configs would look very much alike. This would create a long code with many duplications, which is hard to maintain.
But wait, there is a solution to this !
In general, it provides simplicity and convenience.
More specifically, there is a ConfigMap, in which you can reference other parts of it, even when it's not constructed yet ! That means, you may explicitly express the relations between parts of the configuration - and this removes any duplications.
In addition, it provides a class Configuration, which allows you to have more configurations that inherit key-values from their parents (and this solves our problem in Motivation). Therefore, the code explicitly expresses the structure of a configuration and dependence on other configurations, which makes it much easier to read / maintain.
config = new Configuration();
config.add("master", {
"mode" : $((c) => c['__name__']), // name of the config is stored under a special key
"page": { // you can use nested values
"title": $((c) => "My new homepage - ${c['mode']} mode",
"host": "127.0.0.1"
"port": 8080,
"url": $((c) => 'http://${c['page']['host']}:${c['page']['port']}'), // and reference other values in config
},
"someSocket" : {
"http" : $((c) => c['page']['host'],
"port" : 27001,
}
});
config.add("developer", {
"page" : {
"port" : 8088,
// other parts are inherited
}
}, parent: "master");
config.add("testing", {
"mode" : "test",
"page" : {
"host" : $((c) => "${c['mode']}.example.com",
"url" : $((c) => "http://${c['page']['host']}/"),
}
}, parent: "developer");
config.add("live", {
"page" : {
"title" : "My new homepage",
"url" : "http://example.com/",
},
"someSocket" : {
"port" : 27091,
}
}, parent: "master");
config.get("testing") == {
"__name__" : "testing",
"mode" : "test",
"page" : {
"title" : "My new homepage - test mode",
"host" : "test.example.com",
"port" : 8088,
"url" : "http://test.example.com/",
},
"someSocket" : {
"http" : "test.example.com",
"port" : 27001,
}
};