001/* -*- mode: Java; c-basic-offset: 2; indent-tabs-mode: nil; coding: utf-8-unix -*-
002 *
003 * Copyright © 2020 microBean™.
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
014 * implied.  See the License for the specific language governing
015 * permissions and limitations under the License.
016 */
017package org.microbean.settings;
018
019import java.lang.annotation.Annotation;
020
021import java.util.Collections;
022import java.util.Set;
023
024import javax.enterprise.context.ApplicationScoped;
025
026/**
027 * A {@link Source} that retrieves values from system properties.
028 *
029 * @author <a href="https://about.me/lairdnelson"
030 * target="_parent">Laird Nelson</a>
031 *
032 * @see #getValue(String, Set)
033 */
034@ApplicationScoped
035public class SystemPropertiesSource extends Source {
036
037
038  /*
039   * Constructors.
040   */
041
042
043  /**
044   * Creates a new {@link SystemPropertiesSource}.
045   */
046  public SystemPropertiesSource() {
047    super();
048  }
049
050
051  /*
052   * Instance methods.
053   */
054  
055
056  /**
057   * Returns a {@link Value} suitable for the supplied {@code name} by
058   * making use of the {@link System#getProperty(String)} method.
059   *
060   * @param name the name of the setting; must not be {@code null}
061   *
062   * @param qualifiers a {@link Set} of {@link Annotation}s qualifying
063   * the request; the {@link Value} returned by this method will
064   * {@linkplain Value#getQualifiers() have} a subset of these
065   * qualifiers; must not be {@code null}
066   *
067   * @return a suitable {@link Value}, or {@code null} if an
068   * invocation of {@link System#getProperty(String)} with the
069   * supplied {@code name} returns {@code null}
070   *
071   * @exception NullPointerException if either {@code name} or {@code
072   * qualifiers} is {@code null}
073   *
074   * @threadsafety This method is safe for concurrent use by multiple
075   * threads.
076   *
077   * @idempotency No guarantees with respect to idempotency are made
078   * about this method.
079   *
080   * @nullability This method may return {@code null}.
081   */
082  @Override
083  public Value getValue(final String name, final Set<Annotation> qualifiers) {
084    final Value returnValue;
085    final String stringValue = System.getProperty(name);
086    if (stringValue == null) {
087      returnValue = null;
088    } else {
089      returnValue = new Value(this, name, Collections.emptySet(), false, stringValue);
090    }
091    return returnValue;
092  }
093  
094}