avoid runtime package scanning to discover TypeConverters
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Key: CAMEL-4233
URL: https://issues.apache.org/jira/browse/CAMEL-4233
Project: Camel
Issue Type: Improvement
Reporter: james strachan
Package scanning to discover classes annotated with @Converter is slow. Plus on
many containers (especially commercial JEE containers) its not even possible;
since ClassLoader.getResource() doesn't often return file system based URIs you
can easily convert to a java.io.File so you can list files in a directory.
Finding known resources/classes in class loaders generally works; scanning
packages is generally more problematic - as well as being slow.
So it would be better if Camel could use a text file per jar containing all the
fully qualified class names of the converters to use. Then no package scanning
is required. Or rather we only need to use package scanning if a text file
contains packages (rather than fully qualified classes). i.e. do the package
scanning at build time (when you have full access to the file system :) rather
than at runtime when you generally don't have access to the files - and
expanding jars to look inside them is awfully slow.
In addition it'd be great if we added a maven plugin - or Java compiler
AnnotationProcessor we can use with the compile step - to generate the
META-INF/services/org/apache/camel/TypeConverter file automatically as part of
the build. Then users don't even have to think about it; they just add
@Converter to a class and the plugin generates the text file as part of the
build., using fully qualified class names - so no package scanning required at
runtime - and much faster startup times too
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