    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     https://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 implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.configuration2;
    019
    020import java.util.Collection;
    021import java.util.Map;
    022
    023import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
    024import org.apache.commons.configuration2.interpol.Lookup;
    025import org.apache.commons.configuration2.sync.SynchronizerSupport;
    026
    027/**
    028 * <p>
    029 * The main Configuration interface.
    030 * </p>
    031 * <p>
    032 * This interface allows accessing and manipulating a configuration object. The major part of the methods defined in
    033 * this interface deals with accessing properties of various data types. There is a generic {@code getProperty()}
    034 * method, which returns the value of the queried property in its raw data type. Other getter methods try to convert
    035 * this raw data type into a specific data type. If this fails, a {@code ConversionException} will be thrown.
    036 * </p>
    037 * <p>
    038 * For most of the property getter methods an overloaded version exists that allows to specify a default value, which
    039 * will be returned if the queried property cannot be found in the configuration. The behavior of the methods that do
    040 * not take a default value in case of a missing property is not defined by this interface and depends on a concrete
    041 * implementation. E.g. the {@link AbstractConfiguration} class, which is the base class of most configuration
    042 * implementations provided by this package, per default returns <strong>null</strong> if a property is not found, but provides
    043 * the {@link AbstractConfiguration#setThrowExceptionOnMissing(boolean) setThrowExceptionOnMissing()} method, with which
    044 * it can be configured to throw a {@code NoSuchElementException} exception in that case. (Note that getter methods for
    045 * primitive types in {@code AbstractConfiguration} always throw an exception for missing properties because there is no
    046 * way of overloading the return value.)
    047 * </p>
    048 * <p>
    049 * With the {@code addProperty()} and {@code setProperty()} methods new properties can be added to a configuration or
    050 * the values of properties can be changed. With {@code clearProperty()} a property can be removed. Other methods allow
    051 * to iterate over the contained properties or to create a subset configuration.
    052 * </p>
    053 */
    054public interface Configuration extends ImmutableConfiguration, SynchronizerSupport {
    055
    056    /**
    057     * Add a property to the configuration. If it already exists then the value stated here will be added to the
    058     * configuration entry. For example, if the property:
    059     *
    060     * <pre>
    061     * resource.loader = file
    062     * </pre>
    063     *
    064     * is already present in the configuration and you call
    065     *
    066     * <pre>
    067     * addProperty("resource.loader", "classpath")
    068     * </pre>
    069     *
    070     * Then you will end up with a List like the following:
    071     *
    072     * <pre>
    073     * ["file", "classpath"]
    074     * </pre>
    075     *
    076     * @param key The key to add the property to.
    077     * @param value The value to add.
    078     */
    079    void addProperty(String key, Object value);
    080
    081    /**
    082     * Remove all properties from the configuration.
    083     */
    084    void clear();
    085
    086    /**
    087     * Remove a property from the configuration.
    088     *
    089     * @param key the key to remove along with corresponding value.
    090     */
    091    void clearProperty(String key);
    092
    093    /**
    094     * Gets the {@code ConfigurationInterpolator} object used by this {@code Configuration}. This object is responsible
    095     * for variable substitution.
    096     *
    097     * @return the {@code ConfigurationInterpolator} (can be <strong>null</strong>)
    098     */
    099    ConfigurationInterpolator getInterpolator();
    100
    101    /**
    102     * Creates and installs a new {@code ConfigurationInterpolator} for this {@code Configuration} based on the passed in
    103     * arguments. This method creates a default {@code ConfigurationInterpolator} instance and initializes it with the
    104     * passed in {@code Lookup} objects. It also adds a special default {@code Lookup} object that tries to resolve
    105     * variables by matching them with properties contained in this {@code Configuration}. This is also the main difference
    106     * to the {@link #setInterpolator(ConfigurationInterpolator)} method which sets the passed in object as is without
    107     * adding this special lookup.
    108     *
    109     * @param prefixLookups the map with {@code Lookup} objects associated with specific prefixes (can be <strong>null</strong>)
    110     * @param defLookups a collection with default {@code Lookup} objects (can be <strong>null</strong>)
    111     * @see ConfigurationInterpolator
    112     */
    113    void installInterpolator(Map<String, ? extends Lookup> prefixLookups, Collection<? extends Lookup> defLookups);
    114
    115    /**
    116     * Sets the {@code ConfigurationInterpolator} object to be used by this {@code Configuration}. This object is invoked
    117     * for each access of a string property in order to substitute variables which may be contained. The argument can be
    118     * <strong>null</strong> to disable interpolation at all.
    119     *
    120     * @param ci the new {@code ConfigurationInterpolator}
    121     */
    122    void setInterpolator(ConfigurationInterpolator ci);
    123
    124    /**
    125     * Sets a property, this will replace any previously set values. Set values is implicitly a call to clearProperty(key),
    126     * addProperty(key, value).
    127     *
    128     * @param key The key of the property to change
    129     * @param value The new value
    130     */
    131    void setProperty(String key, Object value);
    132
    133    /**
    134     * Return a decorator Configuration containing every key from the current Configuration that starts with the specified
    135     * prefix. The prefix is removed from the keys in the subset. For example, if the configuration contains the following
    136     * properties:
    137     *
    138     * <pre>
    139     *    prefix.number = 1
    140     *    prefix.string = Apache
    141     *    prefixed.foo = bar
    142     *    prefix = Jakarta
    143     * </pre>
    144     *
    145     * the Configuration returned by {@code subset("prefix")} will contain the properties:
    146     *
    147     * <pre>
    148     *    number = 1
    149     *    string = Apache
    150     *    = Jakarta
    151     * </pre>
    152     *
    153     * (The key for the value "Jakarta" is an empty string)
    154     * <p>
    155     * Since the subset is a decorator and not a modified copy of the initial Configuration, any change made to the subset
    156     * is available to the Configuration, and reciprocally.
    157     *
    158     * @param prefix The prefix used to select the properties.
    159     * @return a subset configuration
    160     * @see SubsetConfiguration
    161     */
    162    Configuration subset(String prefix);
    163}