work/work-runtime/src/main/java/androidx/work/InputMerger.java

/*
 * Copyright 2018 The Android Open Source Project
 *
 * 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 androidx.work;

import androidx.annotation.NonNull;
import androidx.annotation.RestrictTo;

import java.util.List;

/**
 * An abstract class that allows the user to define how to merge a list of inputs to a
 * {@link ListenableWorker}.
 * <p>
 * Before workers run, they receive input {@link Data} from their parent workers, as well as
 * anything specified directly to them via {@link WorkRequest.Builder#setInputData(Data)}.  An
 * InputMerger takes all of these objects and converts them to a single merged {@link Data} to be
 * used as the worker input.  {@link WorkManager} offers two concrete InputMerger implementations:
 * {@link OverwritingInputMerger} and {@link ArrayCreatingInputMerger}.
 * <p>
 * Note that the list of inputs to merge is in an unspecified order.  You should not make
 * assumptions about the order of inputs.
 */

public abstract class InputMerger {

    private static final String TAG = Logger.tagWithPrefix("InputMerger");

    /**
     * Merges a list of {@link Data} and outputs a single Data object.
     *
     * @param inputs A list of {@link Data}
     * @return The merged output
     */
    public abstract @NonNull Data merge(@NonNull List<Data> inputs);

    /**
     * Instantiates an {@link InputMerger} from its class name.
     *
     * @param className The name of the {@link InputMerger} class
     * @return The instantiated {@link InputMerger}, or {@code null} if it could not be instantiated
     *
     * @hide
     */
    @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
    @SuppressWarnings("ClassNewInstance")
    public static InputMerger fromClassName(String className) {
        try {
            Class<?> clazz = Class.forName(className);
            return (InputMerger) clazz.newInstance();
        } catch (Exception e) {
            Logger.get().error(TAG, "Trouble instantiating + " + className, e);
        }
        return null;
    }
}