001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2026 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle;
021
022import java.util.Map;
023import java.util.Properties;
024import java.util.function.Function;
025import java.util.stream.Collectors;
026
027/**
028 * Resolves external properties from an underlying {@code Properties} object.
029 *
030 */
031public final class PropertiesExpander implements PropertyResolver {
032
033    /** The underlying values. */
034    private final Map<String, String> values;
035
036    /**
037     * Creates a new PropertiesExpander.
038     *
039     * @param properties the underlying properties to use for property resolution.
040     * @throws IllegalArgumentException when properties argument is null
041     */
042    public PropertiesExpander(Properties properties) {
043        if (properties == null) {
044            throw new IllegalArgumentException("cannot pass null");
045        }
046        values = properties.stringPropertyNames()
047                .stream()
048                .collect(
049                    Collectors.toUnmodifiableMap(Function.identity(), properties::getProperty));
050    }
051
052    @Override
053    public String resolve(String name) {
054        return values.get(name);
055    }
056
057}