Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.configuration; import java.math.BigDecimal; import java.math.BigInteger; import java.util.Iterator; import java.util.List; import java.util.Properties; /** * <p>The main Configuration interface.</p> * <p>This interface allows accessing and manipulating a configuration object. * The major part of the methods defined in this interface deals with accessing * properties of various data types. There is a generic <code>getProperty()</code> * method, which returns the value of the queried property in its raw data * type. Other getter methods try to convert this raw data type into a specific * data type. If this fails, a <code>ConversionException</code> will be thrown.</p> * <p>For most of the property getter methods an overloaded version exists that * allows to specify a default value, which will be returned if the queried * property cannot be found in the configuration. The behavior of the methods * that do not take a default value in case of a missing property is not defined * by this interface and depends on a concrete implementation. E.g. the * <code>{@link AbstractConfiguration}</code> class, which is the base class * of most configuration implementations provided by this package, per default * returns <b>null</b> if a property is not found, but provides the * <code>{@link org.apache.commons.configuration.AbstractConfiguration#setThrowExceptionOnMissing(boolean) * setThrowExceptionOnMissing()}</code> * method, with which it can be configured to throw a <code>NoSuchElementException</code> * exception in that case. (Note that getter methods for primitive types in * <code>AbstractConfiguration</code> always throw an exception for missing * properties because there is no way of overloading the return value.)</p> * <p>With the <code>addProperty()</code> and <code>setProperty()</code> methods * new properties can be added to a configuration or the values of properties * can be changed. With <code>clearProperty()</code> a property can be removed. * Other methods allow to iterate over the contained properties or to create * a subset configuration.</p> * * @author Commons Configuration team * @version $Id: Configuration.java 449017 2006-09-22 17:27:00Z oheger $ */ public interface Configuration { /** * Return a decorator Configuration containing every key from the current * Configuration that starts with the specified prefix. The prefix is * removed from the keys in the subset. For example, if the configuration * contains the following properties: * * <pre> * prefix.number = 1 * prefix.string = Apache * prefixed.foo = bar * prefix = Jakarta</pre> * * the Configuration returned by <code>subset("prefix")</code> will contain * the properties: * * <pre> * number = 1 * string = Apache * = Jakarta</pre> * * (The key for the value "Jakarta" is an empty string) * <p> * Since the subset is a decorator and not a modified copy of the initial * Configuration, any change made to the subset is available to the * Configuration, and reciprocally. * * @param prefix The prefix used to select the properties. * @return a subset configuration * * @see SubsetConfiguration */ Configuration subset(String prefix); /** * Check if the configuration is empty. * * @return <code>true</code> if the configuration contains no property, * <code>false</code> otherwise. */ boolean isEmpty(); /** * Check if the configuration contains the specified key. * * @param key the key whose presence in this configuration is to be tested * * @return <code>true</code> if the configuration contains a value for this * key, <code>false</code> otherwise */ boolean containsKey(String key); /** * Add a property to the configuration. If it already exists then the value * stated here will be added to the configuration entry. For example, if * the property: * * <pre>resource.loader = file</pre> * * is already present in the configuration and you call * * <pre>addProperty("resource.loader", "classpath")</pre> * * Then you will end up with a List like the following: * * <pre>["file", "classpath"]</pre> * * @param key The key to add the property to. * @param value The value to add. */ void addProperty(String key, Object value); /** * Set a property, this will replace any previously set values. Set values * is implicitly a call to clearProperty(key), addProperty(key, value). * * @param key The key of the property to change * @param value The new value */ void setProperty(String key, Object value); /** * Remove a property from the configuration. * * @param key the key to remove along with corresponding value. */ void clearProperty(String key); /** * Remove all properties from the configuration. */ void clear(); /** * Gets a property from the configuration. This is the most basic get * method for retrieving values of properties. In a typical implementation * of the <code>Configuration</code> interface the other get methods (that * return specific data types) will internally make use of this method. On * this level variable substitution is not yet performed. The returned * object is an internal representation of the property value for the passed * in key. It is owned by the <code>Configuration</code> object. So a caller * should not modify this object. It cannot be guaranteed that this object * will stay constant over time (i.e. further update operations on the * configuration may change its internal state). * * @param key property to retrieve * @return the value to which this configuration maps the specified key, or * null if the configuration contains no mapping for this key. */ Object getProperty(String key); /** * Get the list of the keys contained in the configuration that match the * specified prefix. * * @param prefix The prefix to test against. * @return An Iterator of keys that match the prefix. * @see #getKeys() */ Iterator getKeys(String prefix); /** * Get the list of the keys contained in the configuration. The returned * iterator can be used to obtain all defined keys. Note that the exact * behavior of the iterator's <code>remove()</code> method is specific to * a concrete implementation. It <em>may</em> remove the corresponding * property from the configuration, but this is not guaranteed. In any case * it is no replacement for calling * <code>{@link #clearProperty(String)}</code> for this property. So it is * highly recommended to avoid using the iterator's <code>remove()</code> * method. * * @return An Iterator. */ Iterator getKeys(); /** * Get a list of properties associated with the given configuration key. * This method expects the given key to have an arbitrary number of String * values, each of which is of the form <code>key=value</code>. These * strings are splitted at the equals sign, and the key parts will become * keys of the returned <code>Properties</code> object, the value parts * become values. * * @param key The configuration key. * @return The associated properties if key is found. * * @throws ConversionException is thrown if the key maps to an * object that is not a String/List. * * @throws IllegalArgumentException if one of the tokens is * malformed (does not contain an equals sign). */ Properties getProperties(String key); /** * Get a boolean associated with the given configuration key. * * @param key The configuration key. * @return The associated boolean. * * @throws ConversionException is thrown if the key maps to an * object that is not a Boolean. */ boolean getBoolean(String key); /** * Get a boolean associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated boolean. * * @throws ConversionException is thrown if the key maps to an * object that is not a Boolean. */ boolean getBoolean(String key, boolean defaultValue); /** * Get a {@link Boolean} associated with the given configuration key. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated boolean if key is found and has valid * format, default value otherwise. * * @throws ConversionException is thrown if the key maps to an * object that is not a Boolean. */ Boolean getBoolean(String key, Boolean defaultValue); /** * Get a byte associated with the given configuration key. * * @param key The configuration key. * @return The associated byte. * * @throws ConversionException is thrown if the key maps to an * object that is not a Byte. */ byte getByte(String key); /** * Get a byte associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated byte. * * @throws ConversionException is thrown if the key maps to an * object that is not a Byte. */ byte getByte(String key, byte defaultValue); /** * Get a {@link Byte} associated with the given configuration key. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated byte if key is found and has valid format, default * value otherwise. * * @throws ConversionException is thrown if the key maps to an object that * is not a Byte. */ Byte getByte(String key, Byte defaultValue); /** * Get a double associated with the given configuration key. * * @param key The configuration key. * @return The associated double. * * @throws ConversionException is thrown if the key maps to an * object that is not a Double. */ double getDouble(String key); /** * Get a double associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated double. * * @throws ConversionException is thrown if the key maps to an * object that is not a Double. */ double getDouble(String key, double defaultValue); /** * Get a {@link Double} associated with the given configuration key. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated double if key is found and has valid * format, default value otherwise. * * @throws ConversionException is thrown if the key maps to an * object that is not a Double. */ Double getDouble(String key, Double defaultValue); /** * Get a float associated with the given configuration key. * * @param key The configuration key. * @return The associated float. * @throws ConversionException is thrown if the key maps to an * object that is not a Float. */ float getFloat(String key); /** * Get a float associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated float. * * @throws ConversionException is thrown if the key maps to an * object that is not a Float. */ float getFloat(String key, float defaultValue); /** * Get a {@link Float} associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated float if key is found and has valid * format, default value otherwise. * * @throws ConversionException is thrown if the key maps to an * object that is not a Float. */ Float getFloat(String key, Float defaultValue); /** * Get a int associated with the given configuration key. * * @param key The configuration key. * @return The associated int. * * @throws ConversionException is thrown if the key maps to an * object that is not a Integer. */ int getInt(String key); /** * Get a int associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated int. * * @throws ConversionException is thrown if the key maps to an * object that is not a Integer. */ int getInt(String key, int defaultValue); /** * Get an {@link Integer} associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated int if key is found and has valid format, default * value otherwise. * * @throws ConversionException is thrown if the key maps to an object that * is not a Integer. */ Integer getInteger(String key, Integer defaultValue); /** * Get a long associated with the given configuration key. * * @param key The configuration key. * @return The associated long. * * @throws ConversionException is thrown if the key maps to an * object that is not a Long. */ long getLong(String key); /** * Get a long associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated long. * * @throws ConversionException is thrown if the key maps to an * object that is not a Long. */ long getLong(String key, long defaultValue); /** * Get a {@link Long} associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated long if key is found and has valid * format, default value otherwise. * * @throws ConversionException is thrown if the key maps to an * object that is not a Long. */ Long getLong(String key, Long defaultValue); /** * Get a short associated with the given configuration key. * * @param key The configuration key. * @return The associated short. * * @throws ConversionException is thrown if the key maps to an * object that is not a Short. */ short getShort(String key); /** * Get a short associated with the given configuration key. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated short. * * @throws ConversionException is thrown if the key maps to an * object that is not a Short. */ short getShort(String key, short defaultValue); /** * Get a {@link Short} associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated short if key is found and has valid * format, default value otherwise. * * @throws ConversionException is thrown if the key maps to an * object that is not a Short. */ Short getShort(String key, Short defaultValue); /** * Get a {@link BigDecimal} associated with the given configuration key. * * @param key The configuration key. * @return The associated BigDecimal if key is found and has valid format */ BigDecimal getBigDecimal(String key); /** * Get a {@link BigDecimal} associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * * @return The associated BigDecimal if key is found and has valid * format, default value otherwise. */ BigDecimal getBigDecimal(String key, BigDecimal defaultValue); /** * Get a {@link BigInteger} associated with the given configuration key. * * @param key The configuration key. * * @return The associated BigInteger if key is found and has valid format */ BigInteger getBigInteger(String key); /** * Get a {@link BigInteger} associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * * @return The associated BigInteger if key is found and has valid * format, default value otherwise. */ BigInteger getBigInteger(String key, BigInteger defaultValue); /** * Get a string associated with the given configuration key. * * @param key The configuration key. * @return The associated string. * * @throws ConversionException is thrown if the key maps to an object that * is not a String. */ String getString(String key); /** * Get a string associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated string if key is found and has valid * format, default value otherwise. * * @throws ConversionException is thrown if the key maps to an object that * is not a String. */ String getString(String key, String defaultValue); /** * Get an array of strings associated with the given configuration key. * If the key doesn't map to an existing object an empty array is returned * * @param key The configuration key. * @return The associated string array if key is found. * * @throws ConversionException is thrown if the key maps to an * object that is not a String/List of Strings. */ String[] getStringArray(String key); /** * Get a List of strings associated with the given configuration key. * If the key doesn't map to an existing object an empty List is returned. * * @param key The configuration key. * @return The associated List. * * @throws ConversionException is thrown if the key maps to an * object that is not a List. */ List getList(String key); /** * Get a List of strings associated with the given configuration key. * If the key doesn't map to an existing object, the default value * is returned. * * @param key The configuration key. * @param defaultValue The default value. * @return The associated List of strings. * * @throws ConversionException is thrown if the key maps to an * object that is not a List. */ List getList(String key, List defaultValue); }