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Differences between the CMIS bindings

OpenCMIS supports both the AtomPub and the web services binding interface. It hides all the details how to handle the protocol but there are some subtle differences that need to be reflected in the Java interfaces. This chapter explains where the differences are and why they are needed.

The ObjectInfo interface

The methods in the interfaces CmisService are following the data model in the CMIS specification. The specification defines the following services:

  • AclService
  • DiscoveryService
  • ObjectService
  • MulitfilingService
  • NavigationService
  • PolicyService
  • RelationshipService
  • RepositoryService
  • Versioning Service

For each of these services exists a corresponding interface in opencmis. CmisService is an interface that unifies all interfaces in one interface. The methods in this interface correspond to the methods in the specification. For the web service binding this is a one-to-one mapping. For the AtomPub binding this information is not sufficient in all cases. Take the creation of a document as an example. The web service returns in this case a single string value containing the id of the created document. A response in the AtomPub binding however consists of an AtomPub entry element which is an XML fragment (for an example look at DocumentEntry.xml in the examples directory of the CMIS specification). You will notice that generating this XML requires much more information than the create...() methods in the specification provide as return value. Your implementation needs to provide all the information so that opencmis can generate the complete response. For this purpose the ObjectInfo was introduced. getObjectInfo is the method of the CmisService interface that provides this information. The AbstractCmisService contains a member objectInfoMap that you can fill with this information. If you ignore this the class AbstractCmisService contains a default implementation which works but is very ineffecient. You should use this only as a starting point. Beware that a service can be called from multiple threads, so have to take care to handle threading issues properly.

If the method you are implementing returns a list of objects and not only a single value (for example methods like getChildren(), getDescendants() in the navigation service) you need to provide an ObjectInfo for each element in the collection. getObjectInfo therefore returns a map with the object id for each object as key and the corresponding ObjectInfo as value. You can use the method addObjectInfo to add an element to the map.

The create() methods

The web service binding has separate calls for each object type to be created: policies, relationships, documents and folders:

  • createDocument
  • createFolder
  • createRelationship
  • createPolicy

In the AtomPub binding there is one general create() method that is used for all object types. The CmisObjectService interface therefore contains 5 create() methods, the four specific ones are used for the web service bindings and the general one for the AtomPub binding.