Package com.composum.sling.core.concurrent

Interface LazyCreationService

All Known Implementing Classes:

LazyCreationServiceImpl

public interface LazyCreationService

Service that encapsulates a 'get or create' pattern for resources (incl. possibly a path several parent directories), that adresses the following problems:

• The creation is cluster-safe. If requests in several cluster nodes need the same resource and try to create it at the same time, only one of them will succeed. This should, however, not cause the other requests to fail.
• The user needs the right to read the resource, but shouldn't neccesarily have the right to create or modify the resource. Thus, the creation is done with an admin resolver, but the result is returned with the user's resolver.

An admin resolver is only created when needed.

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	LazyCreationService.CreationStrategy	Strategy to create the resource itself.
static interface	LazyCreationService.InitializationStrategy	Strategy to initialize the resource, if that's a resource intensive task that should be separated from LazyCreationService.CreationStrategy.
static interface	LazyCreationService.ParentCreationStrategy	Strategy to create the parents of the retrieved resource.
static interface	LazyCreationService.RetrievalStrategy<T>	Strategy to retrieve the resources content.

Field Summary

Fields

Modifier and Type	Field	Description
static LazyCreationService.RetrievalStrategy<org.apache.sling.api.resource.Resource>	IDENTITY_RETRIEVER	Simplest LazyCreationService.RetrievalStrategy: just returns the resource.

Method Summary

Modifier and Type	Method	Description
<T> T	getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver, String path, LazyCreationService.RetrievalStrategy<T> getter, LazyCreationService.CreationStrategy creator, LazyCreationService.InitializationStrategy initializer, LazyCreationService.ParentCreationStrategy parentCreationStrategy)	Retrieves a resource or applies a creation and initialization strategy to be carried out with an admin resolver to create it, for resource intensive initialization processes that should not performed twice in the cluster.
<T> T	getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver, String path, LazyCreationService.RetrievalStrategy<T> getter, LazyCreationService.CreationStrategy creator, LazyCreationService.InitializationStrategy initializer, Map<String,Object> parentProperties)	Retrieves a resource or applies a creation and initialization strategy to be carried out with an admin resolver to create it, for resource intensive initialization processes that should not performed twice in the cluster.
<T> T	getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver, String path, LazyCreationService.RetrievalStrategy<T> getter, LazyCreationService.CreationStrategy creator, LazyCreationService.ParentCreationStrategy parentCreationStrategy)	Retrieves a resource or applies a creation strategy to be carried out with an admin resolver to create it.
<T> T	getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver, String path, LazyCreationService.RetrievalStrategy<T> getter, LazyCreationService.CreationStrategy creator, Map<String,Object> parentProperties)	Retrieves a resource or applies a creation strategy to be carried out with an admin resolver to create it.
boolean	isInitialized(org.apache.sling.api.resource.Resource resource)	For resources created by getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, ParentCreationStrategy) or getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, Map), this returns true when the initialization process is finished.
org.apache.sling.api.resource.Resource	waitForInitialization(org.apache.sling.api.resource.ResourceResolver resolver, String path)	For resources created by getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, ParentCreationStrategy) or getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, Map), this returns the resource when the initialization process is finished.

Field Detail

IDENTITY_RETRIEVER

static final LazyCreationService.RetrievalStrategy<org.apache.sling.api.resource.Resource> IDENTITY_RETRIEVER

Simplest LazyCreationService.RetrievalStrategy: just returns the resource.

Method Detail

getOrCreate

<T> T getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver,
                  String path,
                  LazyCreationService.RetrievalStrategy<T> getter,
                  LazyCreationService.CreationStrategy creator,
                  Map<String,Object> parentProperties)
           throws javax.jcr.RepositoryException

Retrieves a resource or applies a creation strategy to be carried out with an admin resolver to create it.

It is an error if getter still returns null after creator is executed.

Type Parameters:

T - the type the LazyCreationService.RetrievalStrategy returns.

Parameters:

resolver - the users resolver. If the resource needed to be created, that is getter returns null, we create it and call a Session.refresh(boolean)(true) on this session before we call getter again. Passed as a parameter to getter.

path - the absolute path at which the creator creates the resource. Passed as a parameter to getter and creator.

getter - side effect free function to retrieve the resource. This can be executed several times in this process.

creator - a strategy to create the resource. Only called when the resource doesn't exist. Is only called after the parent of path is created.

parentProperties - properties with which non-existing parents of path are created (ResourceResolver.create(Resource, String, Map)).

Returns:

the object.

Throws:

javax.jcr.RepositoryException

getOrCreate

<T> T getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver,
                  String path,
                  LazyCreationService.RetrievalStrategy<T> getter,
                  LazyCreationService.CreationStrategy creator,
                  LazyCreationService.ParentCreationStrategy parentCreationStrategy)
           throws javax.jcr.RepositoryException

Retrieves a resource or applies a creation strategy to be carried out with an admin resolver to create it.

It is an error if getter still returns null after creator is executed.

Type Parameters:

T - the type the LazyCreationService.RetrievalStrategy returns.

Parameters:

resolver - the users resolver. If the resource needed to be created, that is getter returns null, we create it and call a Session.refresh(boolean)(true) on this session before we call getter again. Passed as a parameter to getter.

path - the absolute path at which the creator creates the resource. Passed as a parameter to getter and creator.

getter - side effect free function to retrieve the resource. This can be executed several times in this process.

creator - a strategy to create the resource. Only called when the resource doesn't exist. Is only called after the parent of path is created.

parentCreationStrategy - strategy with which non-existing parents of path are created.

Returns:

the object.

Throws:

javax.jcr.RepositoryException

getOrCreate

<T> T getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver,
                  String path,
                  LazyCreationService.RetrievalStrategy<T> getter,
                  LazyCreationService.CreationStrategy creator,
                  LazyCreationService.InitializationStrategy initializer,
                  Map<String,Object> parentProperties)
           throws javax.jcr.RepositoryException,
                  org.apache.sling.api.resource.PersistenceException

Retrieves a resource or applies a creation and initialization strategy to be carried out with an admin resolver to create it, for resource intensive initialization processes that should not performed twice in the cluster. The resource is locked for the cluster with LockManager during that time.

It is an error if getter still returns null after creator is executed.

Type Parameters:

T - the type the LazyCreationService.RetrievalStrategy returns.

Parameters:

resolver - the users resolver. If the resource needed to be created, that is getter returns null, we create it and call a Session.refresh(boolean)(true) on this session before we call getter again. Passed as a parameter to getter.

path - the absolute path at which the creator creates the resource. Passed as a parameter to getter and creator.

getter - side effect free function to retrieve the resource. This can be executed several times in this process.

creator - a strategy to create the resource. Only called when the resource doesn't exist. Is only called after the parent of path is created. This should not perform any resource intensive actions - these should be done in initializer.

initializer - the resource intensive part of the resource creation

parentProperties - properties with which non-existing parents of path are created (ResourceResolver.create(Resource, String, Map)).

Returns:

the object.

Throws:

javax.jcr.RepositoryException

org.apache.sling.api.resource.PersistenceException

getOrCreate

<T> T getOrCreate(org.apache.sling.api.resource.ResourceResolver resolver,
                  String path,
                  LazyCreationService.RetrievalStrategy<T> getter,
                  LazyCreationService.CreationStrategy creator,
                  LazyCreationService.InitializationStrategy initializer,
                  LazyCreationService.ParentCreationStrategy parentCreationStrategy)
           throws javax.jcr.RepositoryException,
                  org.apache.sling.api.resource.PersistenceException

Retrieves a resource or applies a creation and initialization strategy to be carried out with an admin resolver to create it, for resource intensive initialization processes that should not performed twice in the cluster. The resource is locked for the cluster with LockManager during that time.

It is an error if getter still returns null after creator is executed.

Type Parameters:

T - the type the LazyCreationService.RetrievalStrategy returns.

Parameters:

resolver - the users resolver. If the resource needed to be created, that is getter returns null, we create it and call a Session.refresh(boolean)(true) on this session before we call getter again. Passed as a parameter to getter.

path - the absolute path at which the creator creates the resource. Passed as a parameter to getter and creator.

getter - side effect free function to retrieve the resource. This can be executed several times in this process.

creator - a strategy to create the resource. Only called when the resource doesn't exist. Is only called after the parent of path is created.

initializer - the resource intensive part of the resource creation

parentCreationStrategy - strategy with which non-existing parents of path are created.

Returns:

the object.

Throws:

javax.jcr.RepositoryException

org.apache.sling.api.resource.PersistenceException

isInitialized

boolean isInitialized(org.apache.sling.api.resource.Resource resource)
               throws javax.jcr.RepositoryException

For resources created by getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, ParentCreationStrategy) or getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, Map), this returns true when the initialization process is finished.

Throws:

javax.jcr.RepositoryException

waitForInitialization

org.apache.sling.api.resource.Resource waitForInitialization(org.apache.sling.api.resource.ResourceResolver resolver,
                                                             String path)
                                                      throws javax.jcr.RepositoryException

For resources created by getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, ParentCreationStrategy) or getOrCreate(ResourceResolver, String, RetrievalStrategy, CreationStrategy, InitializationStrategy, Map), this returns the resource when the initialization process is finished. If the resource is in creation, this waits a while.

Returns:

the initialized resource, or null if we couldn't find it or it took too long.

Throws:

javax.jcr.RepositoryException