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