    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 */
    017package org.apache.commons.configuration2.builder.fluent;
    018
    019import java.lang.reflect.InvocationHandler;
    020import java.lang.reflect.Method;
    021import java.lang.reflect.Proxy;
    022
    023import org.apache.commons.configuration2.builder.BasicBuilderParameters;
    024import org.apache.commons.configuration2.builder.BuilderParameters;
    025import org.apache.commons.configuration2.builder.DatabaseBuilderParametersImpl;
    026import org.apache.commons.configuration2.builder.DefaultParametersHandler;
    027import org.apache.commons.configuration2.builder.DefaultParametersManager;
    028import org.apache.commons.configuration2.builder.FileBasedBuilderParametersImpl;
    029import org.apache.commons.configuration2.builder.HierarchicalBuilderParametersImpl;
    030import org.apache.commons.configuration2.builder.INIBuilderParametersImpl;
    031import org.apache.commons.configuration2.builder.JndiBuilderParametersImpl;
    032import org.apache.commons.configuration2.builder.PropertiesBuilderParametersImpl;
    033import org.apache.commons.configuration2.builder.XMLBuilderParametersImpl;
    034import org.apache.commons.configuration2.builder.combined.CombinedBuilderParametersImpl;
    035import org.apache.commons.configuration2.builder.combined.MultiFileBuilderParametersImpl;
    036
    037//@formatter:off
    038/**
    039 * A convenience class for creating parameter objects for initializing configuration builder objects.
    040 * <p>
    041 * For setting initialization properties of new configuration objects, a number of specialized parameter classes exists.
    042 * These classes use inheritance to organize the properties they support in a logic way. For instance, parameters for
    043 * file-based configurations also support the basic properties common to all configuration implementations, parameters
    044 * for XML configurations also include file-based and basic properties, etc.
    045 * </p>
    046 * <p>
    047 * When constructing a configuration builder, an easy-to-use fluent API is desired to define specific properties for the
    048 * configuration to be created. However, the inheritance structure of the parameter classes makes it surprisingly
    049 * difficult to provide such an API. This class comes to rescue by defining a set of methods for the creation of
    050 * interface-based parameter objects offering a truly fluent API. The methods provided can be called directly when
    051 * setting up a configuration builder as shown in the following example code fragment:
    052 * </p>
    053 * <pre>
    054 * Parameters params = new Parameters();
    055 * configurationBuilder.configure(params.fileBased()
    056 *   .setThrowExceptionOnMissing(true)
    057 *   .setEncoding(&quot;UTF-8&quot;)
    058 *   .setListDelimiter('#')
    059 *   .setFileName(&quot;test.xml&quot;));
    060 * </pre>
    061 * <p>
    062 * Using this class it is not only possible to create new parameters objects but also to initialize the newly created
    063 * objects with default values. This is via the associated {@link DefaultParametersManager} object. Such an object can
    064 * be passed to the constructor, or a new (uninitialized) instance is created. There are convenience methods for
    065 * interacting with the associated {@code DefaultParametersManager}, namely to register or remove
    066 * {@link DefaultParametersHandler} objects. On all newly created parameters objects the handlers registered at the
    067 * associated {@code DefaultParametersHandler} are automatically applied.
    068 * </p>
    069 * <p>
    070 * Implementation note: This class is thread-safe.
    071 * </p>
    072 *
    073 * @since 2.0
    074 */
    075//@formatter:off
    076public final class Parameters {
    077    /** The manager for default handlers. */
    078    private final DefaultParametersManager defaultParametersManager;
    079
    080    /**
    081     * Creates a new instance of {@code Parameters}. A new, uninitialized {@link DefaultParametersManager} is created.
    082     */
    083    public Parameters() {
    084        this(null);
    085    }
    086
    087    /**
    088     * Creates a new instance of {@code Parameters} and initializes it with the given {@code DefaultParametersManager}.
    089     * Because {@code DefaultParametersManager} is thread-safe, it makes sense to share a single instance between multiple
    090     * {@code Parameters} objects; that way the same initialization is performed on newly created parameters objects.
    091     *
    092     * @param manager the {@code DefaultParametersHandler} (may be <b>null</b>, then a new default instance is created)
    093     */
    094    public Parameters(final DefaultParametersManager manager) {
    095        defaultParametersManager = manager != null ? manager : new DefaultParametersManager();
    096    }
    097
    098    /**
    099     * Returns the {@code DefaultParametersManager} associated with this object.
    100     *
    101     * @return the {@code DefaultParametersManager}
    102     */
    103    public DefaultParametersManager getDefaultParametersManager() {
    104        return defaultParametersManager;
    105    }
    106
    107    /**
    108     * Registers the specified {@code DefaultParametersHandler} object for the given parameters class. This is a convenience
    109     * method which just delegates to the associated {@code DefaultParametersManager}.
    110     *
    111     * @param <T> the type of the parameters supported by this handler
    112     * @param paramsClass the parameters class supported by this handler (must not be <b>null</b>)
    113     * @param handler the {@code DefaultParametersHandler} to be registered (must not be <b>null</b>)
    114     * @throws IllegalArgumentException if a required parameter is missing
    115     * @see DefaultParametersManager
    116     */
    117    public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler) {
    118        getDefaultParametersManager().registerDefaultsHandler(paramsClass, handler);
    119    }
    120
    121    /**
    122     * Registers the specified {@code DefaultParametersHandler} object for the given parameters class and start class in the
    123     * inheritance hierarchy. This is a convenience method which just delegates to the associated
    124     * {@code DefaultParametersManager}.
    125     *
    126     * @param <T> the type of the parameters supported by this handler
    127     * @param paramsClass the parameters class supported by this handler (must not be <b>null</b>)
    128     * @param handler the {@code DefaultParametersHandler} to be registered (must not be <b>null</b>)
    129     * @param startClass an optional start class in the hierarchy of parameter objects for which this handler should be
    130     *        applied
    131     * @throws IllegalArgumentException if a required parameter is missing
    132     */
    133    public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler, final Class<?> startClass) {
    134        getDefaultParametersManager().registerDefaultsHandler(paramsClass, handler, startClass);
    135    }
    136
    137    /**
    138     * Creates a new instance of a parameters object for basic configuration properties.
    139     *
    140     * @return the new parameters object
    141     */
    142    public BasicBuilderParameters basic() {
    143        return new BasicBuilderParameters();
    144    }
    145
    146    /**
    147     * Creates a new instance of a parameters object for file-based configuration properties.
    148     *
    149     * @return the new parameters object
    150     */
    151    public FileBasedBuilderParameters fileBased() {
    152        return createParametersProxy(new FileBasedBuilderParametersImpl(), FileBasedBuilderParameters.class);
    153    }
    154
    155    /**
    156     * Creates a new instance of a parameters object for combined configuration builder properties.
    157     *
    158     * @return the new parameters object
    159     */
    160    public CombinedBuilderParameters combined() {
    161        return createParametersProxy(new CombinedBuilderParametersImpl(), CombinedBuilderParameters.class);
    162    }
    163
    164    /**
    165     * Creates a new instance of a parameters object for JNDI configurations.
    166     *
    167     * @return the new parameters object
    168     */
    169    public JndiBuilderParameters jndi() {
    170        return createParametersProxy(new JndiBuilderParametersImpl(), JndiBuilderParameters.class);
    171    }
    172
    173    /**
    174     * Creates a new instance of a parameters object for hierarchical configurations.
    175     *
    176     * @return the new parameters object
    177     */
    178    public HierarchicalBuilderParameters hierarchical() {
    179        return createParametersProxy(new HierarchicalBuilderParametersImpl(), HierarchicalBuilderParameters.class, FileBasedBuilderParameters.class);
    180    }
    181
    182    /**
    183     * Creates a new instance of a parameters object for XML configurations.
    184     *
    185     * @return the new parameters object
    186     */
    187    public XMLBuilderParameters xml() {
    188        return createParametersProxy(new XMLBuilderParametersImpl(), XMLBuilderParameters.class, FileBasedBuilderParameters.class,
    189            HierarchicalBuilderParameters.class);
    190    }
    191
    192    /**
    193     * Creates a new instance of a parameters object for properties configurations.
    194     *
    195     * @return the new parameters object
    196     */
    197    public PropertiesBuilderParameters properties() {
    198        return createParametersProxy(new PropertiesBuilderParametersImpl(), PropertiesBuilderParameters.class, FileBasedBuilderParameters.class);
    199    }
    200
    201    /**
    202     * Creates a new instance of a parameters object for a builder for multiple file-based configurations.
    203     *
    204     * @return the new parameters object
    205     */
    206    public MultiFileBuilderParameters multiFile() {
    207        return createParametersProxy(new MultiFileBuilderParametersImpl(), MultiFileBuilderParameters.class);
    208    }
    209
    210    /**
    211     * Creates a new instance of a parameters object for database configurations.
    212     *
    213     * @return the new parameters object
    214     */
    215    public DatabaseBuilderParameters database() {
    216        return createParametersProxy(new DatabaseBuilderParametersImpl(), DatabaseBuilderParameters.class);
    217    }
    218
    219    /**
    220     * Creates a new instance of a parameters object for INI configurations.
    221     *
    222     * @return the new parameters object
    223     */
    224    public INIBuilderParameters ini() {
    225        return createParametersProxy(new INIBuilderParametersImpl(), INIBuilderParameters.class, FileBasedBuilderParameters.class,
    226            HierarchicalBuilderParameters.class);
    227    }
    228
    229    /**
    230     * Creates a proxy object for a given parameters interface based on the given implementation object. The newly created
    231     * object is initialized with default values if there are matching {@link DefaultParametersHandler} objects.
    232     *
    233     * @param <T> the type of the parameters interface
    234     * @param target the implementing target object
    235     * @param ifcClass the interface class
    236     * @param superIfcs an array with additional interface classes to be implemented
    237     * @return the proxy object
    238     */
    239    private <T> T createParametersProxy(final Object target, final Class<T> ifcClass, final Class<?>... superIfcs) {
    240        final Class<?>[] ifcClasses = new Class<?>[1 + superIfcs.length];
    241        ifcClasses[0] = ifcClass;
    242        System.arraycopy(superIfcs, 0, ifcClasses, 1, superIfcs.length);
    243        final Object obj = Proxy.newProxyInstance(Parameters.class.getClassLoader(), ifcClasses, new ParametersIfcInvocationHandler(target));
    244        getDefaultParametersManager().initializeParameters((BuilderParameters) obj);
    245        return ifcClass.cast(obj);
    246    }
    247
    248    /**
    249     * A specialized {@code InvocationHandler} implementation which maps the methods of a parameters interface to an
    250     * implementation of the corresponding property interfaces. The parameters interface is a union of multiple property
    251     * interfaces. The wrapped object implements all of these, but not the union interface. Therefore, a reflection-based
    252     * approach is required. A special handling is required for the method of the {@code BuilderParameters} interface
    253     * because here no fluent return value is used.
    254     */
    255    private static class ParametersIfcInvocationHandler implements InvocationHandler {
    256        /** The target object of reflection calls. */
    257        private final Object target;
    258
    259        /**
    260         * Creates a new instance of {@code ParametersIfcInvocationHandler} and sets the wrapped parameters object.
    261         *
    262         * @param targetObj the target object for reflection calls
    263         */
    264        public ParametersIfcInvocationHandler(final Object targetObj) {
    265            target = targetObj;
    266        }
    267
    268        /**
    269         * {@inheritDoc} This implementation delegates method invocations to the target object and handles the return value
    270         * correctly.
    271         */
    272        @Override
    273        public Object invoke(final Object proxy, final Method method, final Object[] args) throws Throwable {
    274            final Object result = method.invoke(target, args);
    275            return isFluentResult(method) ? proxy : result;
    276        }
    277
    278        /**
    279         * Checks whether the specified method belongs to an interface which requires fluent result values.
    280         *
    281         * @param method the method to be checked
    282         * @return a flag whether the method's result should be handled as a fluent result value
    283         */
    284        private static boolean isFluentResult(final Method method) {
    285            final Class<?> declaringClass = method.getDeclaringClass();
    286            return declaringClass.isInterface() && !declaringClass.equals(BuilderParameters.class);
    287        }
    288    }
    289}