Hi
In Camel 3.9 we are introducing optional property placeholders.
https://issues.apache.org/jira/browse/CAMEL-16302
The use-case is to allow configuring Camel endpoints (primarily) where
you can specify some options that may be configured or not (optional).
Currently all property placeholders are mandatory, unless a default
value is provided. So with the default value, you could do "optional"
but then you would need to know what the default value would be (if
there is any).
Optional placeholders is also a feature that we want to have with
route templates (aka Kamelets). So you can create kamelets with a
number of options (some are required, and others would be optional).
And others have default values etc.
The syntax for marking a property placeholder as option is to prefix
the key name with ?, eg
from("jms:cheese?concurrentConsumers={{?speedUp}}")
Here the concurrent consumers option is optional, as the placeholder
value starts with a ? in the key name.
Then the Camel end user can configure the property placeholder, such
as in application.properties
speedUp=5
Or if there are no configuration, then the option is not present and
the endpoint is resolved as:
from("jms:cheese")
The syntax with the ? mark was choose to keep it short. But we are
open for feedback.
Another alternative was to prefix with optional:
{{optional:speedUp}}
However the properties component in Camel then assume the key is named
optional, and the default value is speedUp. So it clashes with this.
But we could make "optional" a reserved word and do special handling
for this.
The only concern about using ? is that an endpoint uri already have ?
for query parameters. And if using more ? would be confusing?
from("jms:cheese?concurrentConsumers={{?speedUp}}&subscrtiptionName={{someName}}")
Any thoughts?
--
Claus Ibsen
-----------------
http://davsclaus.com @davsclaus
Camel in Action 2: https://www.manning.com/ibsen2
