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/**
029 * <p>The main Configuration interface.</p>
030 * <p>This interface allows accessing and manipulating a configuration object.
031 * The major part of the methods defined in this interface deals with accessing
032 * properties of various data types. There is a generic {@code getProperty()}
033 * method, which returns the value of the queried property in its raw data
034 * type. Other getter methods try to convert this raw data type into a specific
035 * data type. If this fails, a {@code ConversionException} will be thrown.</p>
036 * <p>For most of the property getter methods an overloaded version exists that
037 * allows to specify a default value, which will be returned if the queried
038 * property cannot be found in the configuration. The behavior of the methods
039 * that do not take a default value in case of a missing property is not defined
040 * by this interface and depends on a concrete implementation. E.g. the
041 * {@link AbstractConfiguration} class, which is the base class
042 * of most configuration implementations provided by this package, per default
043 * returns <b>null</b> if a property is not found, but provides the
044 * {@link AbstractConfiguration#setThrowExceptionOnMissing(boolean)
045 * setThrowExceptionOnMissing()}
046 * method, with which it can be configured to throw a {@code NoSuchElementException}
047 * exception in that case. (Note that getter methods for primitive types in
048 * {@code AbstractConfiguration} always throw an exception for missing
049 * properties because there is no way of overloading the return value.)</p>
050 * <p>With the {@code addProperty()} and {@code setProperty()} methods
051 * new properties can be added to a configuration or the values of properties
052 * can be changed. With {@code clearProperty()} a property can be removed.
053 * Other methods allow to iterate over the contained properties or to create
054 * a subset configuration.</p>
055 *
056 */
057public interface Configuration extends ImmutableConfiguration, SynchronizerSupport
058{
059    /**
060     * Return a decorator Configuration containing every key from the current
061     * Configuration that starts with the specified prefix. The prefix is
062     * removed from the keys in the subset. For example, if the configuration
063     * contains the following properties:
064     *
065     * <pre>
066     *    prefix.number = 1
067     *    prefix.string = Apache
068     *    prefixed.foo = bar
069     *    prefix = Jakarta</pre>
070     *
071     * the Configuration returned by {@code subset("prefix")} will contain
072     * the properties:
073     *
074     * <pre>
075     *    number = 1
076     *    string = Apache
077     *    = Jakarta</pre>
078     *
079     * (The key for the value "Jakarta" is an empty string)
080     * <p>
081     * Since the subset is a decorator and not a modified copy of the initial
082     * Configuration, any change made to the subset is available to the
083     * Configuration, and reciprocally.
084     *
085     * @param prefix The prefix used to select the properties.
086     * @return a subset configuration
087     *
088     * @see SubsetConfiguration
089     */
090    Configuration subset(String prefix);
091
092    /**
093     * Add a property to the configuration. If it already exists then the value
094     * stated here will be added to the configuration entry. For example, if
095     * the property:
096     *
097     * <pre>resource.loader = file</pre>
098     *
099     * is already present in the configuration and you call
100     *
101     * <pre>addProperty("resource.loader", "classpath")</pre>
102     *
103     * Then you will end up with a List like the following:
104     *
105     * <pre>["file", "classpath"]</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
114     * is implicitly a call to clearProperty(key), 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     * Returns the {@code ConfigurationInterpolator} object used by this
135     * {@code Configuration}. This object is responsible for variable
136     * substitution.
137     *
138     * @return the {@code ConfigurationInterpolator} (can be <b>null</b>)
139     */
140    ConfigurationInterpolator getInterpolator();
141
142    /**
143     * Sets the {@code ConfigurationInterpolator} object to be used by this
144     * {@code Configuration}. This object is invoked for each access of a string
145     * property in order to substitute variables which may be contained. The
146     * argument can be <b>null</b> to disable interpolation at all.
147     *
148     * @param ci the new {@code ConfigurationInterpolator}
149     */
150    void setInterpolator(ConfigurationInterpolator ci);
151
152    /**
153     * Creates and installs a new {@code ConfigurationInterpolator} for this
154     * {@code Configuration} based on the passed in arguments. This method
155     * creates a default {@code ConfigurationInterpolator} instance and
156     * initializes it with the passed in {@code Lookup} objects. It also adds a
157     * special default {@code Lookup} object that tries to resolve variables by
158     * matching them with properties contained in this {@code Configuration}.
159     * This is also the main difference to the
160     * {@link #setInterpolator(ConfigurationInterpolator)} method
161     * which sets the passed in object as is without adding this special lookup.
162     *
163     * @param prefixLookups the map with {@code Lookup} objects associated with
164     *        specific prefixes (can be <b>null</b>)
165     * @param defLookups a collection with default {@code Lookup} objects (can
166     *        be <b>null</b>)
167     * @see ConfigurationInterpolator
168     */
169    void installInterpolator(Map<String, ? extends Lookup> prefixLookups,
170            Collection<? extends Lookup> defLookups);
171}