JarCasting
java-tracerresolver
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.
Tracer resolver
This is a utility class providing a static resolveTracer() method using the JDK ServiceLoader to find declared TracerFactory implementations providing a Tracer.
Tracer factory
A tracer factory implements a getTracer() method and is used by the TracerResolver to look up tracer implementations via a JDK ServiceLoader.
Fallback lookup
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.
Tracer converters
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);
}
}
Priority
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.
GlobalTracer
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.
