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Neo4j kernel is a lightweight, embedded Java database designed to
store data structured as graphs rather than tables. For more
information, see http://neo4j.org.
/**
* Copyright (c) 2002-2013 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see .
*/
package org.neo4j.graphdb;
import java.util.Iterator;
/**
* Find a dependency given a type. This can be the exact type or a super type of
* the actual dependency.
*/
public interface DependencyResolver
{
/**
* Tries to resolve a dependency that matches a given class. No specific
* {@link SelectionStrategy} is used, so the first encountered matching dependency will be returned.
*
* @param type the type of {@link Class} that the returned instance must implement.
* @return the resolved dependency for the given type.
* @throws IllegalArgumentException if no matching dependency was found.
*/
T resolveDependency( Class type ) throws IllegalArgumentException;
/**
* Tries to resolve a dependency that matches a given class. All candidates are fed to the
* {@code selector} which ultimately becomes responsible for making the choice between all available candidates.
*
* @param type the type of {@link Class} that the returned instance must implement.
* @param selector {@link SelectionStrategy} which will make the choice of which one to return among
* matching candidates.
* @return the resolved dependency for the given type.
* @throws IllegalArgumentException if no matching dependency was found.
*/
T resolveDependency( Class type, SelectionStrategy selector ) throws IllegalArgumentException;
/**
* Responsible for making the choice between available candidates.
*/
public interface SelectionStrategy
{
/**
* Given a set of candidates, select an appropriate one. Even if there are candidates this
* method may throw {@link IllegalArgumentException} if there was no suitable candidate.
*
* @param type the type of items.
* @param candidates candidates up for selection, where one should be picked. There might
* also be no suitable candidate, in which case an exception should be thrown.
* @return a suitable candidate among all available.
* @throws IllegalArgumentException if no suitable candidate was found.
*/
T select( Class type, Iterable candidates ) throws IllegalArgumentException;
}
/**
* Adapter for {@link DependencyResolver} which will select the first available candidate by default
* for {@link #resolveDependency(Class)}.
*/
public abstract static class Adapter implements DependencyResolver
{
@SuppressWarnings( "rawtypes" )
private static final SelectionStrategy FIRST = new SelectionStrategy()
{
@Override
public Object select( Class type, Iterable candidates ) throws IllegalArgumentException
{
Iterator iterator = candidates.iterator();
if ( !iterator.hasNext() )
throw new IllegalArgumentException( "Could not resolve dependency of type:" + type.getName() );
return iterator.next();
}
};
@SuppressWarnings( "unchecked" )
private static SelectionStrategy first()
{
return FIRST;
}
@Override
public T resolveDependency( Class type ) throws IllegalArgumentException
{
return resolveDependency( type, Adapter.first() );
}
}
}
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