VaadinSessionScope.java

/*
 *
 *  * Copyright (c) 2016. David Sowerby
 *  *
 *  * 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 uk.q3c.krail.core.guice.vsscope;

import com.google.common.collect.ImmutableList;
import com.google.inject.Key;
import com.google.inject.Provider;
import com.google.inject.Scope;
import com.google.inject.servlet.SessionScoped;
import com.vaadin.server.VaadinSession;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import org.slf4j.Logger;

import java.util.HashMap;
import java.util.Map;

import static org.slf4j.LoggerFactory.getLogger;

/**
 * Provides a Guice scope based on a {@link VaadinSession}. This was necessary because the standard
 * {@link SessionScoped} will only work with a UI (and not things like Views, which where a session scope is most
 * useful) if a UI has server push enabled. See https://github.com/davidsowerby/krail/issues/241
 *
 * @author David Sowerby 2014
 */
@SuppressFBWarnings("CD_CIRCULAR_DEPENDENCY")
public class VaadinSessionScope implements Scope {
    private static Logger log = getLogger(VaadinSessionScope.class);

    private static volatile VaadinSessionScope current;

    private final Map<VaadinSession, Map<Key<?>, Object>> cache = new HashMap<>();

    public VaadinSessionScope() {
        super();
        log.debug("creating VaadinSessionScope {}", this);
    }

    public static VaadinSessionScope getCurrent() {
        // double-checked locking with volatile
        VaadinSessionScope scope = current;
        if (scope == null) {
            synchronized (VaadinSessionScope.class) {
                scope = current;
                if (scope == null) {
                    current = new VaadinSessionScope();
                    scope = current;
                }
            }
        }
        return scope;
    }

    Map<Key<?>, Object> getScopedObjectMap(VaadinSession vaadinSession) {
        // return an existing cache instance
        if (cache.containsKey(vaadinSession)) {
            Map<Key<?>, Object> scopedObjects = cache.get(vaadinSession);
            log.debug("scope cache retrieved for VaadinSession: {}", vaadinSession);
            return scopedObjects;
        } else {
            return createCacheEntry(vaadinSession);
        }
    }

    private Map<Key<?>, Object> createCacheEntry(VaadinSession vaadinSession) {
        Map<Key<?>, Object> sessionEntry = new HashMap<Key<?>, Object>();
        cache.put(vaadinSession, sessionEntry);
        log.debug("created a scope cache for VaadinSessionScope with key: {}", vaadinSession);
        return sessionEntry;
    }

    public void startScope(VaadinSession vaadinSession) {
        if (!cacheHasEntryFor(vaadinSession)) {
            createCacheEntry(vaadinSession);
        }
    }

    public boolean cacheHasEntryFor(VaadinSession vaadinSession) {
        return cache.containsKey(vaadinSession);
    }

    public void releaseScope(VaadinSession vaadinSession) {
        cache.remove(vaadinSession);
    }

    /**
     * Removes all entries in the cache
     */
    public void flush() {
        cache.clear();
    }

    @Override
    public <T> Provider<T> scope(Key<T> key, Provider<T> unscoped) {
        return new VaadinSessionScopeProvider<T>(this, key, unscoped);
    }

    public ImmutableList<VaadinSession> scopeKeys() {
        return ImmutableList.copyOf(cache.keySet());
    }

    public boolean containsInstance(VaadinSession vaadinSession, Object containedInstance) {
        return cache.get(vaadinSession)
                    .containsValue(containedInstance);
    }
}