Resolver API for OpenTracing Tracer implementations.
NOTE: The Tracer Resolver mechanism is only intended to be used at application startup/initialization time.
This responsibility should be handled by the application, possibly using some runtime specific support (e.g. providing a
Tracer @Bean in Spring Boot, or a CDI producer).
Framework integrations used to instrument specific technologies should not use this library, but should allow a Tracer to be injected instead, with fallback to the GlobalTracer.
This is a utility class providing a static resolveTracer() method using
the JDK ServiceLoader to find declared TracerFactory implementations
providing a Tracer.
A tracer factory implements a getTracer() method and is used by the TracerResolver
to look up tracer implementations via a JDK ServiceLoader.
If no TracerFactory is found or no Tracer is returned,
a ServiceLoader lookup for a declared concrete TracerResolver class is used.
This supports the 'legacy' lookup for TracerResolver subclasses providing a resolve() implementation.
Finally, if this also fails, the Tracer class is used as last-resort lookup.
A resolved tracer is passed to all TracerConverter instances that were found.
Tracer converters can be useful for automatically wrapping the resolved Tracer:
public final class FooWrapperConverter implements TracerConverter {
public Tracer convert(Tracer existingTracer) {
return new FooTracerWrapper(existingTracer);
}
}If multiple TracerResolver, TracerConverter or Tracer implementations are found,
they are checked for presence of the @Priority annotation
on their class or superclasses.
The priority is applied as follows:
- First, non-negative priority is applied in natural order (e.g.
0,1,2, ...). - Next, objects without
@Priorityannotation are applied by assigning a default priority ofInteger.MAX_VALUE. - Finally, negative priority is applied in reverse-natural order (e.g.
-1,-2,-3, ...).
The order of objects with equal (implicit) priority is undefined.
If the opentracing-util library is detected and a GlobalTracer
is already-registered, the resolving mechanism will be disabled.
In this case the GlobalTracer is always returned as-is, without applying any converters.