uk.q3c.krail.core.guice.uiscope.UIScopeProvider.java Source code

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Here is the source code for uk.q3c.krail.core.guice.uiscope.UIScopeProvider.java

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/*
 * Copyright (c) 2015. 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.uiscope;

import com.google.inject.Key;
import com.google.inject.Provider;
import com.vaadin.ui.UI;
import com.vaadin.util.CurrentInstance;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import uk.q3c.krail.core.ui.ScopedUI;

import java.util.Map;

/**
 * @param <T>
 *
 * @author David Sowerby
 */
class UIScopeProvider<T> implements Provider<T> {
    private static Logger log = LoggerFactory.getLogger(UIScopeProvider.class);
    private final UIScope uiScope;
    private final Key<T> key;
    private final Provider<T> unscoped;

    UIScopeProvider(UIScope uiScope, Key<T> key, Provider<T> unscoped) {
        this.uiScope = uiScope;
        this.key = key;
        this.unscoped = unscoped;
    }

    @Override
    public T get() {
        // get the scope cache for the current UI
        log.debug("looking for a UIScoped instance of {}", key.getClass().getName());

        // get the current UIKey. It should always be there, as it is created before the UI
        UIKey uiKey = CurrentInstance.get(UIKey.class);
        // this may be null if we are in the process of constructing the UI
        ScopedUI currentUI = (ScopedUI) UI.getCurrent();
        final String msg = "This can happen if you include UIScoped components in your ScopedUIProvider, "
                + "or you are testing and have not set up the test fixture correctly.  For the latter, use TestUIScopeModule, or "
                + "try sub-classing UITestBase and calling createTestUI() or createBasicUI() to prepare the UIScope "
                + "correctly.  If you are not testing please report a bug";
        if (uiKey == null) {
            if (currentUI == null) {
                throw new UIScopeException("UI and uiKey are null. " + msg);
            } else {
                // this can happen when the framework switches UIs
                uiKey = currentUI.getInstanceKey();
                if (uiKey == null) {
                    throw new UIScopeException("uiKey is null and cannot be obtained from the UI. " + msg);
                }
            }
        }

        // currentUI may be null if we are in the process of constructing the UI
        // if not null just check that it hasn't got out of sync with its uikey
        if (currentUI != null) {
            if (!uiKey.equals(currentUI.getInstanceKey())) {
                throw new UIScopeException(
                        "The UI and its UIKey have got out of sync.  Results are unpredictable. " + msg);
            }
        }

        log.debug("looking for cache for key: " + uiKey);
        Map<Key<?>, Object> scopedObjects = this.uiScope.getScopedObjectMap(uiKey);

        // retrieve an existing instance if possible

        @SuppressWarnings("unchecked")
        T current = (T) scopedObjects.get(key);

        if (current != null) {
            log.debug("returning existing instance of " + current.getClass().getSimpleName());
            return current;
        }

        // or create the first instance and cache it
        current = unscoped.get();
        scopedObjects.put(key, current);
        log.debug("new instance of " + current.getClass().getSimpleName() + " created, as none in cache");
        return current;
    }
}