1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.apache.commons.configuration2;
19
20 import java.util.Collection;
21 import java.util.Map;
22
23 import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
24 import org.apache.commons.configuration2.interpol.Lookup;
25 import org.apache.commons.configuration2.sync.SynchronizerSupport;
26
27 /**
28 * <p>
29 * The main Configuration interface.
30 * </p>
31 * <p>
32 * This interface allows accessing and manipulating a configuration object. The major part of the methods defined in
33 * this interface deals with accessing properties of various data types. There is a generic {@code getProperty()}
34 * method, which returns the value of the queried property in its raw data type. Other getter methods try to convert
35 * this raw data type into a specific data type. If this fails, a {@code ConversionException} will be thrown.
36 * </p>
37 * <p>
38 * For most of the property getter methods an overloaded version exists that allows to specify a default value, which
39 * will be returned if the queried property cannot be found in the configuration. The behavior of the methods that do
40 * not take a default value in case of a missing property is not defined by this interface and depends on a concrete
41 * implementation. E.g. the {@link AbstractConfiguration} class, which is the base class of most configuration
42 * implementations provided by this package, per default returns <b>null</b> if a property is not found, but provides
43 * the {@link AbstractConfiguration#setThrowExceptionOnMissing(boolean) setThrowExceptionOnMissing()} method, with which
44 * it can be configured to throw a {@code NoSuchElementException} exception in that case. (Note that getter methods for
45 * primitive types in {@code AbstractConfiguration} always throw an exception for missing properties because there is no
46 * way of overloading the return value.)
47 * </p>
48 * <p>
49 * With the {@code addProperty()} and {@code setProperty()} methods new properties can be added to a configuration or
50 * the values of properties can be changed. With {@code clearProperty()} a property can be removed. Other methods allow
51 * to iterate over the contained properties or to create a subset configuration.
52 * </p>
53 */
54 public interface Configuration extends ImmutableConfiguration, SynchronizerSupport {
55 /**
56 * Add a property to the configuration. If it already exists then the value stated here will be added to the
57 * configuration entry. For example, if the property:
58 *
59 * <pre>
60 * resource.loader = file
61 * </pre>
62 *
63 * is already present in the configuration and you call
64 *
65 * <pre>
66 * addProperty("resource.loader", "classpath")
67 * </pre>
68 *
69 * Then you will end up with a List like the following:
70 *
71 * <pre>
72 * ["file", "classpath"]
73 * </pre>
74 *
75 * @param key The key to add the property to.
76 * @param value The value to add.
77 */
78 void addProperty(String key, Object value);
79
80 /**
81 * Remove all properties from the configuration.
82 */
83 void clear();
84
85 /**
86 * Remove a property from the configuration.
87 *
88 * @param key the key to remove along with corresponding value.
89 */
90 void clearProperty(String key);
91
92 /**
93 * Gets the {@code ConfigurationInterpolator} object used by this {@code Configuration}. This object is responsible
94 * for variable substitution.
95 *
96 * @return the {@code ConfigurationInterpolator} (can be <b>null</b>)
97 */
98 ConfigurationInterpolator getInterpolator();
99
100 /**
101 * Creates and installs a new {@code ConfigurationInterpolator} for this {@code Configuration} based on the passed in
102 * arguments. This method creates a default {@code ConfigurationInterpolator} instance and initializes it with the
103 * passed in {@code Lookup} objects. It also adds a special default {@code Lookup} object that tries to resolve
104 * variables by matching them with properties contained in this {@code Configuration}. This is also the main difference
105 * to the {@link #setInterpolator(ConfigurationInterpolator)} method which sets the passed in object as is without
106 * adding this special lookup.
107 *
108 * @param prefixLookups the map with {@code Lookup} objects associated with specific prefixes (can be <b>null</b>)
109 * @param defLookups a collection with default {@code Lookup} objects (can be <b>null</b>)
110 * @see ConfigurationInterpolator
111 */
112 void installInterpolator(Map<String, ? extends Lookup> prefixLookups, Collection<? extends Lookup> defLookups);
113
114 /**
115 * Sets the {@code ConfigurationInterpolator} object to be used by this {@code Configuration}. This object is invoked
116 * for each access of a string property in order to substitute variables which may be contained. The argument can be
117 * <b>null</b> to disable interpolation at all.
118 *
119 * @param ci the new {@code ConfigurationInterpolator}
120 */
121 void setInterpolator(ConfigurationInterpolator ci);
122
123 /**
124 * Sets a property, this will replace any previously set values. Set values is implicitly a call to clearProperty(key),
125 * addProperty(key, value).
126 *
127 * @param key The key of the property to change
128 * @param value The new value
129 */
130 void setProperty(String key, Object value);
131
132 /**
133 * Return a decorator Configuration containing every key from the current Configuration that starts with the specified
134 * prefix. The prefix is removed from the keys in the subset. For example, if the configuration contains the following
135 * properties:
136 *
137 * <pre>
138 * prefix.number = 1
139 * prefix.string = Apache
140 * prefixed.foo = bar
141 * prefix = Jakarta
142 * </pre>
143 *
144 * the Configuration returned by {@code subset("prefix")} will contain the properties:
145 *
146 * <pre>
147 * number = 1
148 * string = Apache
149 * = Jakarta
150 * </pre>
151 *
152 * (The key for the value "Jakarta" is an empty string)
153 * <p>
154 * Since the subset is a decorator and not a modified copy of the initial Configuration, any change made to the subset
155 * is available to the Configuration, and reciprocally.
156 *
157 * @param prefix The prefix used to select the properties.
158 * @return a subset configuration
159 *
160 * @see SubsetConfiguration
161 */
162 Configuration subset(String prefix);
163 }