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Handler is an interface that can be implemented to support different kinds of metadata. A custom handler can be registered in HandlerFactory. There is ConceptHandler that provides support for org.openmrs.Concept. Apart from that there are OpenmrsMetadataHandler and OpenmrsObjectHandler. They provide with just a basic support for classes implementing OpenmrsMetadata and OpenmrsObject. OpenmrsMetadataHandler in particular determines at runtime a list of classes on the classpath that can be exported.

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Publish/

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subscribe protocol 

Published packages are A published package is accessible through a URL which consists of XXX 5 parts:

1. URL prefix - specifies the application context path and the way the server is accessible can be accessed through the Internet and the application context path. This is typically typically http://localhost:8080/openmrs during in development and and http://example.com/openmrs during in production stage.
2. /ws/rest/metadatasharing/package/  to follow OpenMRS REST patterns
3. UUID of the package group (a mutual UUID along all package versions)
4. /latest which indicates that the subscriber will lookup for the latest version of from the package group
5. (optional) .form suffix required on OpenMRS versions which don't support webservicesdo not support web services. Note: after upgrading OpenMRS from e.g. 1.6.x to 1.8.1 version +, the publish URLs will lose this suffix, but old URLs will remain accessible. 

Example of a publish URL: http:/localhost:8080/openmrs/ws/rest/metadatasharing/package/7f2d4731-0a98-4118-8fe0-d4b9731986c6/latest

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The download URL is similar to publish URL, but it ends with: %VERSION/download. This allows us to download any published version of the package, but this feature isn't is not used yet.