org.osgi.service.resolver.ResolveContext Maven / Gradle / Ivy
/*
* Copyright (c) OSGi Alliance (2011, 2013). All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.osgi.service.resolver;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import org.osgi.resource.Capability;
import org.osgi.resource.Requirement;
import org.osgi.resource.Resource;
import org.osgi.resource.Wiring;
/**
* A resolve context provides resources, options and constraints to the
* potential solution of a {@link Resolver#resolve(ResolveContext) resolve}
* operation.
*
*
* Resolve Contexts:
*
* - Specify the mandatory and optional resources to resolve. The mandatory
* and optional resources must be consistent and correct. For example, they must
* not violate the singleton policy of the implementer.
* - Provide {@link Capability capabilities} that the Resolver can use to
* satisfy {@link Requirement requirements} via the
* {@link #findProviders(Requirement)} method
* - Constrain solutions via the {@link #getWirings()} method. A wiring
* consists of a map of existing {@link Resource resources} to {@link Wiring
* wiring}.
* - Filter requirements that are part of a resolve operation via the
* {@link #isEffective(Requirement)}.
*
*
*
* A resolver may call the methods on the resolve context any number of times
* during a resolve operation using any thread. Implementors should ensure that
* this class is properly thread safe.
*
*
* Except for {@link #insertHostedCapability(List, HostedCapability)}, the
* resolve context methods must be idempotent. This means that resources
* must have constant capabilities and requirements and the resolve context must
* return a consistent set of capabilities, wires and effective requirements.
*
* @ThreadSafe
* @author $Id: 31e6bd75deae054742a168e7d5b76915b07cbb54 $
*/
public abstract class ResolveContext {
/**
* Return the resources that must be resolved for this resolve context.
*
*
* The default implementation returns an empty collection.
*
* @return The resources that must be resolved for this resolve context. May
* be empty if there are no mandatory resources.
*/
public Collection getMandatoryResources() {
return emptyCollection();
}
/**
* Return the resources that the resolver should attempt to resolve for this
* resolve context. Inability to resolve one of the specified resources will
* not result in a resolution exception.
*
*
* The default implementation returns an empty collection.
*
* @return The resources that the resolver should attempt to resolve for
* this resolve context. May be empty if there are no mandatory
* resources.
*/
public Collection getOptionalResources() {
return emptyCollection();
}
private static Collection emptyCollection() {
return Collections.EMPTY_LIST;
}
/**
* Find Capabilities that match the given Requirement.
*
* The returned list contains {@link Capability} objects where the Resource
* must be the declared Resource of the Capability. The Resolver can then
* add additional {@link HostedCapability} objects with the
* {@link #insertHostedCapability(List, HostedCapability)} method when it,
* for example, attaches fragments. Those {@link HostedCapability} objects
* will then use the host's Resource which likely differs from the declared
* Resource of the corresponding Capability.
*
*
* The returned list is in priority order such that the Capabilities with a
* lower index have a preference over those with a higher index. The
* resolver must use the
* {@link #insertHostedCapability(List, HostedCapability)} method to add
* additional Capabilities to maintain priority order. In general, this is
* necessary when the Resolver uses Capabilities declared in a Resource but
* that must originate from an attached host.
*
*
* Each returned Capability must match the given Requirement. This implies
* that the filter in the Requirement must match as well as any namespace
* specific directives. For example, the mandatory attributes for the
* {@code osgi.wiring.package} namespace.
*
* @param requirement The requirement that a resolver is attempting to
* satisfy. Must not be {@code null}.
* @return A list of {@link Capability} objects that match the specified
* requirement.
*/
public abstract List findProviders(Requirement requirement);
/**
* Add a {@link HostedCapability} to the list of capabilities returned from
* {@link #findProviders(Requirement)}.
*
*
* This method is used by the {@link Resolver} to add Capabilities that are
* hosted by another Resource to the list of Capabilities returned from
* {@link #findProviders(Requirement)}. This function is necessary to allow
* fragments to attach to hosts, thereby changing the origin of a
* Capability. This method must insert the specified HostedCapability in a
* place that makes the list maintain the preference order. It must return
* the index in the list of the inserted {@link HostedCapability}.
*
* @param capabilities The list returned from
* {@link #findProviders(Requirement)}. Must not be {@code null}.
* @param hostedCapability The HostedCapability to insert in the specified
* list. Must not be {@code null}.
* @return The index in the list of the inserted HostedCapability.
*
*/
public abstract int insertHostedCapability(List capabilities, HostedCapability hostedCapability);
/**
* Test if a given requirement should be wired in the resolve operation. If
* this method returns {@code false}, then the resolver should ignore this
* requirement during the resolve operation.
*
*
* The primary use case for this is to test the {@code effective} directive
* on the requirement, though implementations are free to use any effective
* test.
*
* @param requirement The Requirement to test. Must not be {@code null}.
* @return {@code true} if the requirement should be considered as part of
* the resolve operation.
*/
public abstract boolean isEffective(Requirement requirement);
/**
* Returns the wirings for existing resolved resources.
*
*
* For example, if this resolve context is for an OSGi framework, then the
* result would contain all the currently resolved bundles with each
* bundle's current wiring.
*
*
* Multiple calls to this method for this resolve context must return the
* same result.
*
* @return The wirings for existing resolved resources. The returned map is
* unmodifiable.
*/
public abstract Map getWirings();
}