    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 *     https://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    /**
    078     * A specialized {@code InvocationHandler} implementation which maps the methods of a parameters interface to an
    079     * implementation of the corresponding property interfaces. The parameters interface is a union of multiple property
    080     * interfaces. The wrapped object implements all of these, but not the union interface. Therefore, a reflection-based
    081     * approach is required. A special handling is required for the method of the {@code BuilderParameters} interface
    082     * because here no fluent return value is used.
    083     */
    084    private static final class ParametersIfcInvocationHandler implements InvocationHandler {
    085        /**
    086         * Checks whether the specified method belongs to an interface which requires fluent result values.
    087         *
    088         * @param method the method to be checked
    089         * @return a flag whether the method's result should be handled as a fluent result value
    090         */
    091        private static boolean isFluentResult(final Method method) {
    092            final Class<?> declaringClass = method.getDeclaringClass();
    093            return declaringClass.isInterface() && !declaringClass.equals(BuilderParameters.class);
    094        }
    095
    096        /** The target object of reflection calls. */
    097        private final Object target;
    098
    099        /**
    100         * Creates a new instance of {@code ParametersIfcInvocationHandler} and sets the wrapped parameters object.
    101         *
    102         * @param targetObj the target object for reflection calls
    103         */
    104        public ParametersIfcInvocationHandler(final Object targetObj) {
    105            target = targetObj;
    106        }
    107
    108        /**
    109         * {@inheritDoc} This implementation delegates method invocations to the target object and handles the return value
    110         * correctly.
    111         */
    112        @Override
    113        public Object invoke(final Object proxy, final Method method, final Object[] args) throws Throwable {
    114            final Object result = method.invoke(target, args);
    115            return isFluentResult(method) ? proxy : result;
    116        }
    117    }
    118
    119    /** The manager for default handlers. */
    120    private final DefaultParametersManager defaultParametersManager;
    121
    122    /**
    123     * Creates a new instance of {@code Parameters}. A new, uninitialized {@link DefaultParametersManager} is created.
    124     */
    125    public Parameters() {
    126        this(null);
    127    }
    128
    129    /**
    130     * Creates a new instance of {@code Parameters} and initializes it with the given {@code DefaultParametersManager}.
    131     * Because {@code DefaultParametersManager} is thread-safe, it makes sense to share a single instance between multiple
    132     * {@code Parameters} objects; that way the same initialization is performed on newly created parameters objects.
    133     *
    134     * @param manager the {@code DefaultParametersHandler} (may be <strong>null</strong>, then a new default instance is created)
    135     */
    136    public Parameters(final DefaultParametersManager manager) {
    137        defaultParametersManager = manager != null ? manager : new DefaultParametersManager();
    138    }
    139
    140    /**
    141     * Creates a new instance of a parameters object for basic configuration properties.
    142     *
    143     * @return the new parameters object
    144     */
    145    public BasicBuilderParameters basic() {
    146        return new BasicBuilderParameters();
    147    }
    148
    149    /**
    150     * Creates a new instance of a parameters object for combined configuration builder properties.
    151     *
    152     * @return the new parameters object
    153     */
    154    public CombinedBuilderParameters combined() {
    155        return createParametersProxy(new CombinedBuilderParametersImpl(), CombinedBuilderParameters.class);
    156    }
    157
    158    /**
    159     * Creates a proxy object for a given parameters interface based on the given implementation object. The newly created
    160     * object is initialized with default values if there are matching {@link DefaultParametersHandler} objects.
    161     *
    162     * @param <T> the type of the parameters interface
    163     * @param target the implementing target object
    164     * @param ifcClass the interface class
    165     * @param superIfcs an array with additional interface classes to be implemented
    166     * @return the proxy object
    167     */
    168    private <T> T createParametersProxy(final Object target, final Class<T> ifcClass, final Class<?>... superIfcs) {
    169        final Class<?>[] ifcClasses = new Class<?>[1 + superIfcs.length];
    170        ifcClasses[0] = ifcClass;
    171        System.arraycopy(superIfcs, 0, ifcClasses, 1, superIfcs.length);
    172        final Object obj = Proxy.newProxyInstance(Parameters.class.getClassLoader(), ifcClasses, new ParametersIfcInvocationHandler(target));
    173        getDefaultParametersManager().initializeParameters((BuilderParameters) obj);
    174        return ifcClass.cast(obj);
    175    }
    176
    177    /**
    178     * Creates a new instance of a parameters object for database configurations.
    179     *
    180     * @return the new parameters object
    181     */
    182    public DatabaseBuilderParameters database() {
    183        return createParametersProxy(new DatabaseBuilderParametersImpl(), DatabaseBuilderParameters.class);
    184    }
    185
    186    /**
    187     * Creates a new instance of a parameters object for file-based configuration properties.
    188     *
    189     * @return the new parameters object
    190     */
    191    public FileBasedBuilderParameters fileBased() {
    192        return createParametersProxy(new FileBasedBuilderParametersImpl(), FileBasedBuilderParameters.class);
    193    }
    194
    195    /**
    196     * Gets the {@code DefaultParametersManager} associated with this object.
    197     *
    198     * @return the {@code DefaultParametersManager}
    199     */
    200    public DefaultParametersManager getDefaultParametersManager() {
    201        return defaultParametersManager;
    202    }
    203
    204    /**
    205     * Creates a new instance of a parameters object for hierarchical configurations.
    206     *
    207     * @return the new parameters object
    208     */
    209    public HierarchicalBuilderParameters hierarchical() {
    210        return createParametersProxy(new HierarchicalBuilderParametersImpl(), HierarchicalBuilderParameters.class, FileBasedBuilderParameters.class);
    211    }
    212
    213    /**
    214     * Creates a new instance of a parameters object for INI configurations.
    215     *
    216     * @return the new parameters object
    217     */
    218    public INIBuilderParameters ini() {
    219        return createParametersProxy(new INIBuilderParametersImpl(), INIBuilderParameters.class, FileBasedBuilderParameters.class,
    220            HierarchicalBuilderParameters.class);
    221    }
    222
    223    /**
    224     * Creates a new instance of a parameters object for JNDI configurations.
    225     *
    226     * @return the new parameters object
    227     */
    228    public JndiBuilderParameters jndi() {
    229        return createParametersProxy(new JndiBuilderParametersImpl(), JndiBuilderParameters.class);
    230    }
    231
    232    /**
    233     * Creates a new instance of a parameters object for a builder for multiple file-based configurations.
    234     *
    235     * @return the new parameters object
    236     */
    237    public MultiFileBuilderParameters multiFile() {
    238        return createParametersProxy(new MultiFileBuilderParametersImpl(), MultiFileBuilderParameters.class);
    239    }
    240
    241    /**
    242     * Creates a new instance of a parameters object for properties configurations.
    243     *
    244     * @return the new parameters object
    245     */
    246    public PropertiesBuilderParameters properties() {
    247        return createParametersProxy(new PropertiesBuilderParametersImpl(), PropertiesBuilderParameters.class, FileBasedBuilderParameters.class);
    248    }
    249
    250    /**
    251     * Registers the specified {@code DefaultParametersHandler} object for the given parameters class. This is a convenience
    252     * method which just delegates to the associated {@code DefaultParametersManager}.
    253     *
    254     * @param <T> the type of the parameters supported by this handler
    255     * @param paramsClass the parameters class supported by this handler (must not be <strong>null</strong>)
    256     * @param handler the {@code DefaultParametersHandler} to be registered (must not be <strong>null</strong>)
    257     * @throws IllegalArgumentException if a required parameter is missing
    258     * @see DefaultParametersManager
    259     */
    260    public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler) {
    261        getDefaultParametersManager().registerDefaultsHandler(paramsClass, handler);
    262    }
    263
    264    /**
    265     * Registers the specified {@code DefaultParametersHandler} object for the given parameters class and start class in the
    266     * inheritance hierarchy. This is a convenience method which just delegates to the associated
    267     * {@code DefaultParametersManager}.
    268     *
    269     * @param <T> the type of the parameters supported by this handler
    270     * @param paramsClass the parameters class supported by this handler (must not be <strong>null</strong>)
    271     * @param handler the {@code DefaultParametersHandler} to be registered (must not be <strong>null</strong>)
    272     * @param startClass an optional start class in the hierarchy of parameter objects for which this handler should be
    273     *        applied
    274     * @throws IllegalArgumentException if a required parameter is missing
    275     */
    276    public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler, final Class<?> startClass) {
    277        getDefaultParametersManager().registerDefaultsHandler(paramsClass, handler, startClass);
    278    }
    279
    280    /**
    281     * Creates a new instance of a parameters object for XML configurations.
    282     *
    283     * @return the new parameters object
    284     */
    285    public XMLBuilderParameters xml() {
    286        return createParametersProxy(new XMLBuilderParametersImpl(), XMLBuilderParameters.class, FileBasedBuilderParameters.class,
    287            HierarchicalBuilderParameters.class);
    288    }
    289}