InstanceProvidedByUtil.java

/*
 * Copyright (c) 2016 Red Hat, Inc. and others. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.netvirt.aclservice.tests.utils.inject;

import java.lang.reflect.Method;
import javax.inject.Provider;

/**
 * Utility for {@link InstanceProvidedBy}.
 *
 * <p>
 * Used internally by {@link ProviderRunner}; not typically intended for direct
 * end-user usage.
 *
 * @author Michael Vorburger
 */
public class InstanceProvidedByUtil {

    public Object getInstance(Class<?> classAnnotatedWithInjectorProvider)
            throws InstanceProvidedByAnnotationException, ReflectiveOperationException {

        InstanceProvidedBy annotation = classAnnotatedWithInjectorProvider.getAnnotation(InstanceProvidedBy.class);
        if (annotation == null) {
            throw new InstanceProvidedByAnnotationException(classAnnotatedWithInjectorProvider
                    + " must be annotated with " + InstanceProvidedBy.class.getName());
        }
        Class<? extends Provider<?>> providerClass = annotation.value();
        return getInstance(classAnnotatedWithInjectorProvider, providerClass);
    }

    protected Object getInstance(Class<?> classAnnotatedWithInjectorProvider,
            Class<? extends Provider<?>> providerClass)
            throws InstanceProvidedByAnnotationException, ReflectiveOperationException {

        Provider<?> provider = getProvider(providerClass);
        Object instance = provider.get();

        if (!classAnnotatedWithInjectorProvider.equals(instance.getClass())) {
            throw new InstanceProvidedByAnnotationException(
                    classAnnotatedWithInjectorProvider + " @" + InstanceProvidedBy.class.getSimpleName() + "'s "
                            + providerClass + "'s get() created an instance of " + instance.getClass().getName()
                            + " instead of an " + classAnnotatedWithInjectorProvider);
        }
        return instance;
    }

    protected Provider<?> getProvider(Class<? extends Provider<?>> providerClass) throws ReflectiveOperationException {

        // Could here easily also first check if providerClass has a visible
        // default constructor, not needed with Dagger; but could be useful for
        // other usages later

        Method providerClassStaticCreateMethod = providerClass.getMethod("create");
        Provider<?> provider = (Provider<?>) providerClassStaticCreateMethod.invoke(null);
        return provider;
    }

}