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https://issues.apache.org/activemq/browse/CAMEL-1385?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Willem Jiang reassigned CAMEL-1385:
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Assignee: Willem Jiang
> allow the (transitive) maven dependencies on a module to be displayed in the
> runtime when we fail to load a component/language/converter
> ----------------------------------------------------------------------------------------------------------------------------------------
>
> Key: CAMEL-1385
> URL: https://issues.apache.org/activemq/browse/CAMEL-1385
> Project: Apache Camel
> Issue Type: Improvement
> Reporter: James Strachan
> Assignee: Willem Jiang
> Fix For: 2.1.0
>
>
> It can be frustrating seeing lots of stack traces with random
> ClassNotFoundException. Its also pretty hard to know what jars are required
> for any component. While folks using Maven don't always have this issue -
> folks who slap jars into a WEB-INF/lib directory or use Ant - frequently miss
> jars from the classpath.
> When we try to load a class for a component, language, converter (or any
> other auto-discovery mechanisms we have) we should know the 'camel module'
> and therefore the dependencies it requires. e.g. if resolving the "jms"
> component we should know its "camel-jms" doing the lookup. Then we can look
> in some canonical place for the list of jar dependencies
> (groupId/artifactId/version) which camel-jms requires and then inform the
> user of the dependencies it requires. e.g. we look for
> org.apache.camel.jms.dependencies.properties on the classpath and use that to
> list the actual compile time dependencies (generated at build time from
> maven).
> FWIW there's a maven plugin I hacked for servicemix which does something
> kinda similar - dumping maven dependencies into a properties file (so you
> don't need to depend on some maven library stuff to be able to easily grok
> what your dependencies are).
> http://svn.apache.org/repos/asf/servicemix/maven-plugins/depends-maven-plugin/trunk/
> which generates a dependencies file
> http://svn.apache.org/repos/asf/servicemix/maven-plugins/depends-maven-plugin/trunk/src/main/java/org/apache/servicemix/tooling/depends/GenerateDependsFileMojo.java
> So I'm thinking we should put a dependencies file in the package that the
> component/language/converters are defined in - then that single file can be
> looked up by any code and shared across component/language/converter
> discovery.
> So we could reuse the same plugin - but just overload the output file to
> change from
> {code}
> ${project.build.directory}/classes/META-INF/maven/dependencies.properties
> {code}
> to be
> {code}
> ${project.build.directory}/classes/META-INF/maven/org/apache/camel/jms/dependencies.properties
> {code}
> e.g. put a file org.apache.camel.jms.dependencies.properties on the
> classpath; then when loading a component/language/converter class in that
> package, we look for the dependencies properties file (and maybe keep walking
> up the package hierarchy until we find one).
> Then whenever we try to load a component/language/converter (or indeed do any
> String -> class conversion) we can discover the available
> $package/dependencies.properties files and use that information to produce
> useful warnings about missing classes etc.
> It'd be awesome if we could list the actual *missing* library :).
> e.g. if you try and use "activemq" component and stuff is missing on the
> classpath (and we seem to see something like this alot on the forums etc)....
> {code}
> WARN: Camel tried to load the 'activemq' component defined in
> org.apache.activemq:activemq-camel:5.3.0 but you were missing the following
> jars from your classpath org.apache.geronimo.specs:jta.jar:1.234, ....
> {code}
> However even if we just had a way to list the dependencies we expect and the
> user could do the diff themselves it'd be really helpful. (I wonder if we can
> figure out if a jar is present on the classpath based on a
> groupId/artifactId/version? - maybe looking internally for the pom.xml that
> Maven shoves in META-INF?).
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