Configuration Flavors

[Anatole Tresch]

Configuration Flavors

This discussion is about configuration flavors, meaning the type of configuration that should be possible. Most of configuration libraries on the market on a low level are using Strings as main representation type of configuration. Though for many use cases this is completely sufficient, I think configuration should support basically also other types:

• All basic data types such as Boolean, Character, Byte, Short, Long, Float, Double, BigDecimal, BigInteger.
• Collections and arrays.
• But also binary types may be supported, e.g. for reading jars, wars or ears for configuring a deployment.

As a consequence we might define a ConfigEntry similar like

public interface ConfigEntry<T>{

  CLass<T> getEntryType();

  T getValue();

  String getKey();

  String getOrigin();

  // to be discussed later/separatelly:

  //   - scope

  //   - attributes

}

Note that a ConfigEntry models the generic container for a configuration entry, not how the API for access may look like.

[nicolas de loof]

I don't actually understand a use case to configure binary types.

For all other data types, can be converted from a String representation - typically can use JSON syntax for structured data.

[Anatole Tresch]

JSON is only one way to structure data.

[nicolas de loof]

sure, just a sample. Can be xml, yaml, or whatever the JVM can convert to structured data a standard way. JAXB and (future) JSONB can help here

[Juven Xu]

I am also not getting the use case for binary, others are good.

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[nicolas de loof]

I especially can't image how you expect such a binary entry to be manageable, if it's not human readable. 

Defining a configuration item as a URL to "some managed resource" is ok, but as a binary stream ? How do you expect ops to set and check value is well set ?

2013/10/26 Juven Xu <juve...@gmail.com>

[Anatole Tresch]

Just to clarify: the config entry is a String. The value accessed can be an InputStream, e.g. using an adapter that reads the URL...

[Anatole Tresch]

To more clearer, I would suggest the code as follows:

String myURLValue = config.getProperty("myURL");   // "http://bar.foo/someFoo.css"

URL myURL = config.getProperty("myURL", ConfigAdapters.getURLAdapter());  // new URL("http://bar.foo/someFoo.css")

InputStream is = config.getProperty("myURL", ConfigAdapters.getURLInputStreamAdapter();  

     // new URL("http://bar.foo/someFoo.css").openStream(), or buffered using a SoftReference and a internal cache...

On the signature of Configuration it would be:

public String getProperty(String key);

public String getProperty(String key, String defaultValue);

public Integer getIntProperty(String key);

public Integer getIntProperty(String key, Integer defaultValue);

...

public <T> T getProperty(String key, PropertyAdapter<T> adapter);

public <T> T getProperty(String key, PropertyAdapter<T> adapter,  T defaultValue);

whereas

@FunctionalInterface

public interface PropertyAdapter{

   T adapt(String value);

}

2013/10/28 Anatole Tresch <atst...@gmail.com>

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Anatole Tresch

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[Juven Xu]

This is really an nice extension point, users can adapt to whatever object they want.

Although I don’t see many use cases where it’s very necessary, but since adapting to Integer does not diff much from adapting to URL, I say +1.

Thanks,

Juven