Mark Raynsford created QPID-8670:
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Summary: Please provide an explicit method of passing in providers
Key: QPID-8670
URL: https://issues.apache.org/jira/browse/QPID-8670
Project: Qpid
Issue Type: Improvement
Components: Broker-J
Affects Versions: qpid-java-broker-9.2.0
Reporter: Mark Raynsford
Currently, the only way the broker can pick up "plugins" is via ServiceLoader.
Specifically, it seems that all extensions to the broker must be provided by
registering a provider as a service, and then the following code inside the
SystemLauncher uses ServiceLoader to find it:
```
private void startupImpl(Map<String,Object> systemConfigAttributes) throws
Exception
{
populateSystemPropertiesFromDefaults((String)
systemConfigAttributes.get(SystemConfig.INITIAL_SYSTEM_PROPERTIES_LOCATION));
String storeType = (String)
systemConfigAttributes.get(SystemConfig.TYPE);
// Create the RootLogger to be used during broker operation
boolean statusUpdatesEnabled =
Boolean.parseBoolean(System.getProperty(SystemConfig.PROPERTY_STATUS_UPDATES,
"true"));
MessageLogger messageLogger = new
LoggingMessageLogger(statusUpdatesEnabled);
_eventLogger.setMessageLogger(messageLogger);
PluggableFactoryLoader<SystemConfigFactory> configFactoryLoader = new
PluggableFactoryLoader<>(SystemConfigFactory.class);
```
However, this is rather painful to deal with when we want to package Broker-J
as part of a reusable library so that the broker can be embedded in other
applications.
My use case is that I want to provide a very simplified API that doesn't expose
any of Broker-J's APIs to the user. When the user starts a broker, they
explicitly pass in a list of authentication providers that are implemented in
terms of my simplified interfaces.
In the current world, the only way for new authentication providers to be added
is if implementations of the ConfiguredObjectFactory type can be located by the
Broker-J implementation via ServiceLoader. ServiceLoader is not dynamic (at
least not without making the system completely incomprehensible).
I would really appreciate a method to pass in a list of ConfiguredObjectFactory
values to the system rather than having it unconditionally find them via
ServiceLoader. It would be fine if the explicit factories passed in were used
in addition to anything found in ServiceLoader.
This would also, presumably, make testing easier: ServiceLoader is not the
easiest thing in the world to mock due to being quite tied to the module system
and other VM internals.
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