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 *     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 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 <b>null</b> 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     * Return a decorator Configuration containing every key from the current Configuration that starts with the specified
057     * prefix. The prefix is removed from the keys in the subset. For example, if the configuration contains the following
058     * properties:
059     *
060     * <pre>
061     *    prefix.number = 1
062     *    prefix.string = Apache
063     *    prefixed.foo = bar
064     *    prefix = Jakarta
065     * </pre>
066     *
067     * the Configuration returned by {@code subset("prefix")} will contain the properties:
068     *
069     * <pre>
070     *    number = 1
071     *    string = Apache
072     *    = Jakarta
073     * </pre>
074     *
075     * (The key for the value "Jakarta" is an empty string)
076     * <p>
077     * Since the subset is a decorator and not a modified copy of the initial Configuration, any change made to the subset
078     * is available to the Configuration, and reciprocally.
079     *
080     * @param prefix The prefix used to select the properties.
081     * @return a subset configuration
082     *
083     * @see SubsetConfiguration
084     */
085    Configuration subset(String prefix);
086
087    /**
088     * Add a property to the configuration. If it already exists then the value stated here will be added to the
089     * configuration entry. For example, if the property:
090     *
091     * <pre>
092     * resource.loader = file
093     * </pre>
094     *
095     * is already present in the configuration and you call
096     *
097     * <pre>
098     * addProperty("resource.loader", "classpath")
099     * </pre>
100     *
101     * Then you will end up with a List like the following:
102     *
103     * <pre>
104     * ["file", "classpath"]
105     * </pre>
106     *
107     * @param key The key to add the property to.
108     * @param value The value to add.
109     */
110    void addProperty(String key, Object value);
111
112    /**
113     * Set a property, this will replace any previously set values. Set values is implicitly a call to clearProperty(key),
114     * addProperty(key, value).
115     *
116     * @param key The key of the property to change
117     * @param value The new value
118     */
119    void setProperty(String key, Object value);
120
121    /**
122     * Remove a property from the configuration.
123     *
124     * @param key the key to remove along with corresponding value.
125     */
126    void clearProperty(String key);
127
128    /**
129     * Remove all properties from the configuration.
130     */
131    void clear();
132
133    /**
134     * Gets the {@code ConfigurationInterpolator} object used by this {@code Configuration}. This object is responsible
135     * for variable substitution.
136     *
137     * @return the {@code ConfigurationInterpolator} (can be <b>null</b>)
138     */
139    ConfigurationInterpolator getInterpolator();
140
141    /**
142     * Sets the {@code ConfigurationInterpolator} object to be used by this {@code Configuration}. This object is invoked
143     * for each access of a string property in order to substitute variables which may be contained. The argument can be
144     * <b>null</b> to disable interpolation at all.
145     *
146     * @param ci the new {@code ConfigurationInterpolator}
147     */
148    void setInterpolator(ConfigurationInterpolator ci);
149
150    /**
151     * Creates and installs a new {@code ConfigurationInterpolator} for this {@code Configuration} based on the passed in
152     * arguments. This method creates a default {@code ConfigurationInterpolator} instance and initializes it with the
153     * passed in {@code Lookup} objects. It also adds a special default {@code Lookup} object that tries to resolve
154     * variables by matching them with properties contained in this {@code Configuration}. This is also the main difference
155     * to the {@link #setInterpolator(ConfigurationInterpolator)} method which sets the passed in object as is without
156     * adding this special lookup.
157     *
158     * @param prefixLookups the map with {@code Lookup} objects associated with specific prefixes (can be <b>null</b>)
159     * @param defLookups a collection with default {@code Lookup} objects (can be <b>null</b>)
160     * @see ConfigurationInterpolator
161     */
162    void installInterpolator(Map<String, ? extends Lookup> prefixLookups, Collection<? extends Lookup> defLookups);
163}