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These are just a few common tools shared across various vlingo projects.

There is a newer version: 1.7.5

// Copyright © 2012-2020 VLINGO LABS. All rights reserved.
//
// This Source Code Form is subject to the terms of the
// Mozilla Public License, v. 2.0. If a copy of the MPL
// was not distributed with this file, You can obtain
// one at https://mozilla.org/MPL/2.0/.

package io.vlingo.common.config;

import java.util.Properties;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Properties implementation that supports interpolating properties from environment
 * variable values.
 *
 * 

 * Value syntax: ${<env var name>[:<default value>]}
 *
 * 

 * Examples:
 *
 * 
 *     a=${FOO}; FOO=bar -> a=bar
 *     a=${FOO}trag${BAZ}; FOO=un; BAZ=bar -> a=untragbar
 *     a=${FOO:qux}; FOO=bar; -> a=bar
 *     a=${FOO:qux}; FOO=<not set> -> a=qux
 * 
 */
public class EnvVarProperties extends Properties {
    private static final long serialVersionUID = 1L;

    private static final Pattern envVarPattern = Pattern.compile("\\$\\{(?[0-9a-zA-Z_]+)(:(?[^\\}]+))?\\}");

    /**
     * Checks if the value contains a sequence to be interpolated (${<ENV_VAR>}) and
     * replaces it with the value of the corresponding environment variable.
     * 
     * Default values can be specified after a colon in the variable: ${ENV_VAR:default}
     * 
     * The implementation overrides put of the underlying HashMap
     * to hook into the process of setting the value.
     *
     * @throws IllegalArgumentException if the environment variable is not set or either key or value are null
     * @see Properties#setProperty
     * @see Properties#load
     */
    @Override
    public synchronized Object put(Object key, Object value) {
        ensureKeyAndValueAreStrings(key, value);

        StringBuffer interpolated = new StringBuffer();
        Matcher matcher = envVarPattern.matcher((String) value);

        while (matcher.find()) {
            String envVal = System.getenv(matcher.group("envVar"));
            String defaultVal = matcher.group("default");

            ensureValueOrDefault((String) key, envVal, defaultVal);
            matcher.appendReplacement(interpolated, envVal == null ? defaultVal : envVal);
        }
        matcher.appendTail(interpolated);

        return super.put(key, interpolated.toString());
    }

    private void ensureKeyAndValueAreStrings(Object key, Object value) {
        if (!(key instanceof String && value instanceof String)) {
            throw new IllegalArgumentException("Both key and value need to be Strings");
        }
    }

    private void ensureValueOrDefault(String key, String envVal, String defaultVal) {
        if (envVal == null && defaultVal == null) {
            throw new IllegalArgumentException("Environment variable " + key + " not set and has no default.");
        }
    }
}