    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.combined;
    018
    019import java.lang.reflect.Constructor;
    020import java.util.ArrayList;
    021import java.util.Collection;
    022import java.util.Collections;
    023import java.util.Map;
    024
    025import org.apache.commons.configuration2.Configuration;
    026import org.apache.commons.configuration2.ConfigurationUtils;
    027import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
    028import org.apache.commons.configuration2.builder.BuilderParameters;
    029import org.apache.commons.configuration2.builder.ConfigurationBuilder;
    030import org.apache.commons.configuration2.ex.ConfigurationException;
    031
    032/**
    033 * <p>
    034 * A fully-functional, reflection-based implementation of the
    035 * {@code ConfigurationBuilderProvider} interface which can deal with the
    036 * default tags defining configuration sources.
    037 * </p>
    038 * <p>
    039 * An instance of this class is initialized with the names of the
    040 * {@code ConfigurationBuilder} class used by this provider and the concrete
    041 * {@code Configuration} class. The {@code ConfigurationBuilder} class must be
    042 * derived from {@link BasicConfigurationBuilder}. When asked for the builder
    043 * object, an instance of the builder class is created and initialized from the
    044 * bean declaration associated with the current configuration source.
    045 * </p>
    046 * <p>
    047 * {@code ConfigurationBuilder} objects are configured using parameter objects.
    048 * When declaring configuration sources in XML it should not be necessary to
    049 * define the single parameter objects. Rather, simple and complex properties
    050 * are set in the typical way of a bean declaration (i.e. as attributes of the
    051 * current XML element or as child elements). This class creates all supported
    052 * parameter objects (whose names also must be provided at construction time)
    053 * and takes care that their properties are initialized according to the current
    054 * bean declaration.
    055 * </p>
    056 * <p>
    057 * The use of reflection to create builder instances allows a generic
    058 * implementation supporting many concrete builder classes. Another reason for
    059 * this approach is that builder classes are only loaded if actually needed.
    060 * Some specialized {@code Configuration} implementations require specific
    061 * external dependencies which should not be mandatory for the use of
    062 * {@code CombinedConfigurationBuilder}. Because such classes are lazily loaded,
    063 * an application only has to include the dependencies it actually uses.
    064 * </p>
    065 *
    066 * @since 2.0
    067 */
    068public class BaseConfigurationBuilderProvider implements
    069        ConfigurationBuilderProvider
    070{
    071    /** The types of the constructor parameters for a basic builder. */
    072    private static final Class<?>[] CTOR_PARAM_TYPES = {
    073            Class.class, Map.class, Boolean.TYPE
    074    };
    075
    076    /** The name of the builder class. */
    077    private final String builderClass;
    078
    079    /** The name of a builder class with reloading support. */
    080    private final String reloadingBuilderClass;
    081
    082    /** Stores the name of the configuration class to be created. */
    083    private final String configurationClass;
    084
    085    /** A collection with the names of parameter classes. */
    086    private final Collection<String> parameterClasses;
    087
    088    /**
    089     * Creates a new instance of {@code BaseConfigurationBuilderProvider} and
    090     * initializes all its properties.
    091     *
    092     * @param bldrCls the name of the builder class (must not be <b>null</b>)
    093     * @param reloadBldrCls the name of a builder class to be used if reloading
    094     *        support is required (<b>null</b> if reloading is not supported)
    095     * @param configCls the name of the configuration class (must not be
    096     *        <b>null</b>)
    097     * @param paramCls a collection with the names of parameters classes
    098     * @throws IllegalArgumentException if a required parameter is missing
    099     */
    100    public BaseConfigurationBuilderProvider(final String bldrCls,
    101            final String reloadBldrCls, final String configCls, final Collection<String> paramCls)
    102    {
    103        if (bldrCls == null)
    104        {
    105            throw new IllegalArgumentException(
    106                    "Builder class must not be null!");
    107        }
    108        if (configCls == null)
    109        {
    110            throw new IllegalArgumentException(
    111                    "Configuration class must not be null!");
    112        }
    113
    114        builderClass = bldrCls;
    115        reloadingBuilderClass = reloadBldrCls;
    116        configurationClass = configCls;
    117        parameterClasses = initParameterClasses(paramCls);
    118    }
    119
    120    /**
    121     * Returns the name of the class of the builder created by this provider.
    122     *
    123     * @return the builder class
    124     */
    125    public String getBuilderClass()
    126    {
    127        return builderClass;
    128    }
    129
    130    /**
    131     * Returns the name of the class of the builder created by this provider if
    132     * the reload flag is set. If this method returns <b>null</b>, reloading
    133     * builders are not supported by this provider.
    134     *
    135     * @return the reloading builder class
    136     */
    137    public String getReloadingBuilderClass()
    138    {
    139        return reloadingBuilderClass;
    140    }
    141
    142    /**
    143     * Returns the name of the configuration class created by the builder
    144     * produced by this provider.
    145     *
    146     * @return the configuration class
    147     */
    148    public String getConfigurationClass()
    149    {
    150        return configurationClass;
    151    }
    152
    153    /**
    154     * Returns an unmodifiable collection with the names of parameter classes
    155     * supported by this provider.
    156     *
    157     * @return the parameter classes
    158     */
    159    public Collection<String> getParameterClasses()
    160    {
    161        return parameterClasses;
    162    }
    163
    164    /**
    165     * {@inheritDoc} This implementation delegates to some protected methods to
    166     * create a new builder instance using reflection and to configure it with
    167     * parameter values defined by the passed in {@code BeanDeclaration}.
    168     */
    169    @Override
    170    public ConfigurationBuilder<? extends Configuration> getConfigurationBuilder(
    171            final ConfigurationDeclaration decl) throws ConfigurationException
    172    {
    173        try
    174        {
    175            final Collection<BuilderParameters> params = createParameterObjects();
    176            initializeParameterObjects(decl, params);
    177            final BasicConfigurationBuilder<? extends Configuration> builder =
    178                    createBuilder(decl, params);
    179            configureBuilder(builder, decl, params);
    180            return builder;
    181        }
    182        catch (final ConfigurationException cex)
    183        {
    184            throw cex;
    185        }
    186        catch (final Exception ex)
    187        {
    188            throw new ConfigurationException(ex);
    189        }
    190    }
    191
    192    /**
    193     * Determines the <em>allowFailOnInit</em> flag for the newly created
    194     * builder based on the given {@code ConfigurationDeclaration}. Some
    195     * combinations of flags in the declaration say that a configuration source
    196     * is optional, but an empty instance should be created if its creation
    197     * fail.
    198     *
    199     * @param decl the current {@code ConfigurationDeclaration}
    200     * @return the value of the <em>allowFailOnInit</em> flag
    201     */
    202    protected boolean isAllowFailOnInit(final ConfigurationDeclaration decl)
    203    {
    204        return decl.isOptional() && decl.isForceCreate();
    205    }
    206
    207    /**
    208     * Creates a collection of parameter objects to be used for configuring the
    209     * builder. This method creates instances of the parameter classes passed to
    210     * the constructor.
    211     *
    212     * @return a collection with parameter objects for the builder
    213     * @throws Exception if an error occurs while creating parameter objects via
    214     *         reflection
    215     */
    216    protected Collection<BuilderParameters> createParameterObjects()
    217            throws Exception
    218    {
    219        final Collection<BuilderParameters> params =
    220                new ArrayList<>(
    221                        getParameterClasses().size());
    222        for (final String paramcls : getParameterClasses())
    223        {
    224            params.add(createParameterObject(paramcls));
    225        }
    226        return params;
    227    }
    228
    229    /**
    230     * Initializes the parameter objects with data stored in the current bean
    231     * declaration. This method is called before the newly created builder
    232     * instance is configured with the parameter objects. It maps attributes of
    233     * the bean declaration to properties of parameter objects. In addition,
    234     * it invokes the parent {@code CombinedConfigurationBuilder} so that the
    235     * parameters object can inherit properties already defined for this
    236     * builder.
    237     *
    238     * @param decl the current {@code ConfigurationDeclaration}
    239     * @param params the collection with (uninitialized) parameter objects
    240     * @throws Exception if an error occurs
    241     */
    242    protected void initializeParameterObjects(final ConfigurationDeclaration decl,
    243            final Collection<BuilderParameters> params) throws Exception
    244    {
    245        inheritParentBuilderProperties(decl, params);
    246        final MultiWrapDynaBean wrapBean = new MultiWrapDynaBean(params);
    247        decl.getConfigurationBuilder().initBean(wrapBean, decl);
    248    }
    249
    250    /**
    251     * Passes all parameter objects to the parent
    252     * {@code CombinedConfigurationBuilder} so that properties already defined
    253     * for the parent builder can be added. This method is called before the
    254     * parameter objects are initialized from the definition configuration. This
    255     * way properties from the parent builder are inherited, but can be
    256     * overridden for child configurations.
    257     *
    258     * @param decl the current {@code ConfigurationDeclaration}
    259     * @param params the collection with (uninitialized) parameter objects
    260     */
    261    protected void inheritParentBuilderProperties(
    262            final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
    263    {
    264        for (final BuilderParameters p : params)
    265        {
    266            decl.getConfigurationBuilder().initChildBuilderParameters(p);
    267        }
    268    }
    269
    270    /**
    271     * Creates a new, uninitialized instance of the builder class managed by
    272     * this provider. This implementation determines the builder class to be
    273     * used by delegating to {@code determineBuilderClass()}. It then calls the
    274     * constructor expecting the configuration class, the map with properties,
    275     * and the<em>allowFailOnInit</em> flag.
    276     *
    277     * @param decl the current {@code ConfigurationDeclaration}
    278     * @param params initialization parameters for the new builder object
    279     * @return the newly created builder instance
    280     * @throws Exception if an error occurs
    281     */
    282    protected BasicConfigurationBuilder<? extends Configuration> createBuilder(
    283            final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
    284            throws Exception
    285    {
    286        final Class<?> bldCls =
    287                ConfigurationUtils.loadClass(determineBuilderClass(decl));
    288        final Class<?> configCls =
    289                ConfigurationUtils.loadClass(determineConfigurationClass(decl,
    290                        params));
    291        final Constructor<?> ctor = bldCls.getConstructor(CTOR_PARAM_TYPES);
    292        // ? extends Configuration is the minimum constraint
    293        @SuppressWarnings("unchecked")
    294        final
    295        BasicConfigurationBuilder<? extends Configuration> builder =
    296                (BasicConfigurationBuilder<? extends Configuration>) ctor
    297                        .newInstance(configCls, null, isAllowFailOnInit(decl));
    298        return builder;
    299    }
    300
    301    /**
    302     * Configures a newly created builder instance with its initialization
    303     * parameters. This method is called after a new instance was created using
    304     * reflection. This implementation passes the parameter objects to the
    305     * builder's {@code configure()} method.
    306     *
    307     * @param builder the builder to be initialized
    308     * @param decl the current {@code ConfigurationDeclaration}
    309     * @param params the collection with initialization parameter objects
    310     * @throws Exception if an error occurs
    311     */
    312    protected void configureBuilder(
    313            final BasicConfigurationBuilder<? extends Configuration> builder,
    314            final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
    315            throws Exception
    316    {
    317        builder.configure(params.toArray(new BuilderParameters[params.size()]));
    318    }
    319
    320    /**
    321     * Determines the name of the class to be used for a new builder instance.
    322     * This implementation selects between the normal and the reloading builder
    323     * class, based on the passed in {@code ConfigurationDeclaration}. If a
    324     * reloading builder is desired, but this provider has no reloading support,
    325     * an exception is thrown.
    326     *
    327     * @param decl the current {@code ConfigurationDeclaration}
    328     * @return the name of the builder class
    329     * @throws ConfigurationException if the builder class cannot be determined
    330     */
    331    protected String determineBuilderClass(final ConfigurationDeclaration decl)
    332            throws ConfigurationException
    333    {
    334        if (decl.isReload())
    335        {
    336            if (getReloadingBuilderClass() == null)
    337            {
    338                throw new ConfigurationException(
    339                        "No support for reloading for builder class "
    340                                + getBuilderClass());
    341            }
    342            return getReloadingBuilderClass();
    343        }
    344        return getBuilderClass();
    345    }
    346
    347    /**
    348     * Determines the name of the configuration class produced by the builder.
    349     * This method is called when obtaining the arguments for invoking the
    350     * constructor of the builder class. This implementation just returns the
    351     * pre-configured configuration class name. Derived classes may determine
    352     * this class name dynamically based on the passed in parameters.
    353     *
    354     * @param decl the current {@code ConfigurationDeclaration}
    355     * @param params the collection with parameter objects
    356     * @return the name of the builder's result configuration class
    357     * @throws ConfigurationException if an error occurs
    358     */
    359    protected String determineConfigurationClass(final ConfigurationDeclaration decl,
    360            final Collection<BuilderParameters> params) throws ConfigurationException
    361    {
    362        return getConfigurationClass();
    363    }
    364
    365    /**
    366     * Creates an instance of a parameter class using reflection.
    367     *
    368     * @param paramcls the parameter class
    369     * @return the newly created instance
    370     * @throws Exception if an error occurs
    371     */
    372    private static BuilderParameters createParameterObject(final String paramcls)
    373            throws Exception
    374    {
    375        final Class<?> cls = ConfigurationUtils.loadClass(paramcls);
    376        final BuilderParameters p = (BuilderParameters) cls.newInstance();
    377        return p;
    378    }
    379
    380    /**
    381     * Creates a new, unmodifiable collection for the parameter classes.
    382     *
    383     * @param paramCls the collection with parameter classes passed to the
    384     *        constructor
    385     * @return the collection to be stored
    386     */
    387    private static Collection<String> initParameterClasses(
    388            final Collection<String> paramCls)
    389    {
    390        if (paramCls == null)
    391        {
    392            return Collections.emptySet();
    393        }
    394        return Collections.unmodifiableCollection(new ArrayList<>(
    395                paramCls));
    396    }
    397}