updater_sample/src/com/example/android/systemupdatersample/util/UpdateConfigs.java

/*
 * Copyright (C) 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 com.example.android.systemupdatersample.util;

import android.content.Context;

import com.example.android.systemupdatersample.UpdateConfig;

import java.io.File;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

/**
 * Utility class for working with json update configurations.
 */
public final class UpdateConfigs {

    private static final String UPDATE_CONFIGS_ROOT = "configs/";

    /**
     * @param configs update configs
     * @return list of names
     */
    public static String[] configsToNames(List<UpdateConfig> configs) {
        return configs.stream().map(UpdateConfig::getName).toArray(String[]::new);
    }

    /**
     * @param context app context
     * @return configs root directory
     */
    public static String getConfigsRoot(Context context) {
        return Paths.get(context.getFilesDir().toString(),
                UPDATE_CONFIGS_ROOT).toString();
    }

    /**
     * It parses only {@code .json} files.
     *
     * @param context application context
     * @return list of configs from directory {@link UpdateConfigs#getConfigsRoot}
     */
    public static List<UpdateConfig> getUpdateConfigs(Context context) {
        File root = new File(getConfigsRoot(context));
        ArrayList<UpdateConfig> configs = new ArrayList<>();
        if (!root.exists()) {
            return configs;
        }
        for (final File f : root.listFiles()) {
            if (!f.isDirectory() && f.getName().endsWith(".json")) {
                try {
                    String json = new String(Files.readAllBytes(f.toPath()),
                            StandardCharsets.UTF_8);
                    configs.add(UpdateConfig.fromJson(json));
                } catch (Exception e) {
                    throw new RuntimeException(
                            "Can't read/parse config file " + f.getName(), e);
                }
            }
        }
        return configs;
    }

    private UpdateConfigs() {}
}