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A lightweight abstraction for configuration access

There is a newer version: 0.25.1

/**
 * Copyright (C) Telicent Ltd
 *
 * 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 io.telicent.smart.cache.configuration.sources;

import java.util.Objects;
import java.util.Properties;

/**
 * A configuration source backed by a Java {@link Properties} object
 */
public class PropertiesSource implements ConfigurationSource {

    private final Properties properties;

    /**
     * Properties to use as the configuration source
     *
     * @param properties Properties
     */
    public PropertiesSource(Properties properties) {
        Objects.requireNonNull("Properties cannot be null");
        this.properties = properties;
    }

    @Override
    public String get(String key) {
        return getFromProperties(this.properties, key);
    }

    /**
     * Gets a configuration value from the given {@link Properties} object
     * 
     * This will convert the provided {@code key} into System property style key using
     * {@link ConfigurationSource#asSystemPropertyKey(String)} and use that as the primary search key.  If the value
     * does not exist with that key within the given properties then it falls back
     * 
     *
     * @param properties Properties
     * @param key        Key
     * @return Value (if available), otherwise {@code null}
     */
    static String getFromProperties(Properties properties, String key) {
        String variableKey = ConfigurationSource.asSystemPropertyKey(key);
        String value = properties.getProperty(variableKey);
        // May be stored as a non-String property in which case just convert toString()
        // Or may be stored with the key exactly, not the key as converted to a system property style key
        if (value == null && properties.containsKey(variableKey)) {
            value = properties.get(variableKey).toString();
        } else if (value == null && properties.containsKey(key)) {
            value = properties.get(key).toString();
        }
        return value;
    }
}