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 * @author Commons Configuration team
057 */
058public interface Configuration extends ImmutableConfiguration, SynchronizerSupport
059{
060    /**
061     * Return a decorator Configuration containing every key from the current
062     * Configuration that starts with the specified prefix. The prefix is
063     * removed from the keys in the subset. For example, if the configuration
064     * contains the following properties:
065     *
066     * <pre>
067     *    prefix.number = 1
068     *    prefix.string = Apache
069     *    prefixed.foo = bar
070     *    prefix = Jakarta</pre>
071     *
072     * the Configuration returned by {@code subset("prefix")} will contain
073     * the properties:
074     *
075     * <pre>
076     *    number = 1
077     *    string = Apache
078     *    = Jakarta</pre>
079     *
080     * (The key for the value "Jakarta" is an empty string)
081     * <p>
082     * Since the subset is a decorator and not a modified copy of the initial
083     * Configuration, any change made to the subset is available to the
084     * Configuration, and reciprocally.
085     *
086     * @param prefix The prefix used to select the properties.
087     * @return a subset configuration
088     *
089     * @see SubsetConfiguration
090     */
091    Configuration subset(String prefix);
092
093    /**
094     * Add a property to the configuration. If it already exists then the value
095     * stated here will be added to the configuration entry. For example, if
096     * the property:
097     *
098     * <pre>resource.loader = file</pre>
099     *
100     * is already present in the configuration and you call
101     *
102     * <pre>addProperty("resource.loader", "classpath")</pre>
103     *
104     * Then you will end up with a List like the following:
105     *
106     * <pre>["file", "classpath"]</pre>
107     *
108     * @param key The key to add the property to.
109     * @param value The value to add.
110     */
111    void addProperty(String key, Object value);
112
113    /**
114     * Set a property, this will replace any previously set values. Set values
115     * is implicitly a call to clearProperty(key), addProperty(key, value).
116     *
117     * @param key The key of the property to change
118     * @param value The new value
119     */
120    void setProperty(String key, Object value);
121
122    /**
123     * Remove a property from the configuration.
124     *
125     * @param key the key to remove along with corresponding value.
126     */
127    void clearProperty(String key);
128
129    /**
130     * Remove all properties from the configuration.
131     */
132    void clear();
133
134    /**
135     * Returns the {@code ConfigurationInterpolator} object used by this
136     * {@code Configuration}. This object is responsible for variable
137     * substitution.
138     *
139     * @return the {@code ConfigurationInterpolator} (can be <b>null</b>)
140     */
141    ConfigurationInterpolator getInterpolator();
142
143    /**
144     * Sets the {@code ConfigurationInterpolator} object to be used by this
145     * {@code Configuration}. This object is invoked for each access of a string
146     * property in order to substitute variables which may be contained. The
147     * argument can be <b>null</b> to disable interpolation at all.
148     *
149     * @param ci the new {@code ConfigurationInterpolator}
150     */
151    void setInterpolator(ConfigurationInterpolator ci);
152
153    /**
154     * Creates and installs a new {@code ConfigurationInterpolator} for this
155     * {@code Configuration} based on the passed in arguments. This method
156     * creates a default {@code ConfigurationInterpolator} instance and
157     * initializes it with the passed in {@code Lookup} objects. It also adds a
158     * special default {@code Lookup} object that tries to resolve variables by
159     * matching them with properties contained in this {@code Configuration}.
160     * This is also the main difference to the
161     * {@link #setInterpolator(ConfigurationInterpolator)} method
162     * which sets the passed in object as is without adding this special lookup.
163     *
164     * @param prefixLookups the map with {@code Lookup} objects associated with
165     *        specific prefixes (can be <b>null</b>)
166     * @param defLookups a collection with default {@code Lookup} objects (can
167     *        be <b>null</b>)
168     * @see ConfigurationInterpolator
169     */
170    void installInterpolator(Map<String, ? extends Lookup> prefixLookups,
171            Collection<? extends Lookup> defLookups);
172}