Source code
Description: source: package: org.apache.commons.configuration2.builder.combined, class: BaseConfigurationBuilderProvider

    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.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
    062    /** The types of the constructor parameters for a basic builder. */
    063    private static final Class<?>[] CTOR_PARAM_TYPES = {Class.class, Map.class, Boolean.TYPE};
    064
    065    /**
    066     * Creates an instance of a parameter class using reflection.
    067     *
    068     * @param paramcls the parameter class
    069     * @return the newly created instance
    070     * @throws Exception if an error occurs
    071     */
    072    private static BuilderParameters createParameterObject(final String paramcls) throws ReflectiveOperationException {
    073        return (BuilderParameters) ConfigurationUtils.loadClass(paramcls).getConstructor().newInstance();
    074    }
    075
    076    /**
    077     * Creates a new, unmodifiable collection for the parameter classes.
    078     *
    079     * @param paramCls the collection with parameter classes passed to the constructor
    080     * @return the collection to be stored
    081     */
    082    private static Collection<String> initParameterClasses(final Collection<String> paramCls) {
    083        if (paramCls == null) {
    084            return Collections.emptySet();
    085        }
    086        return Collections.unmodifiableCollection(new ArrayList<>(paramCls));
    087    }
    088
    089    /** The name of the builder class. */
    090    private final String builderClass;
    091
    092    /** The name of a builder class with reloading support. */
    093    private final String reloadingBuilderClass;
    094
    095    /** Stores the name of the configuration class to be created. */
    096    private final String configurationClass;
    097
    098    /** A collection with the names of parameter classes. */
    099    private final Collection<String> parameterClasses;
    100
    101    /**
    102     * Creates a new instance of {@code BaseConfigurationBuilderProvider} and initializes all its properties.
    103     *
    104     * @param bldrCls the name of the builder class (must not be <strong>null</strong>)
    105     * @param reloadBldrCls the name of a builder class to be used if reloading support is required (<strong>null</strong> if
    106     *        reloading is not supported)
    107     * @param configCls the name of the configuration class (must not be <strong>null</strong>)
    108     * @param paramCls a collection with the names of parameters classes
    109     * @throws IllegalArgumentException if a required parameter is missing
    110     */
    111    public BaseConfigurationBuilderProvider(final String bldrCls, final String reloadBldrCls, final String configCls, final Collection<String> paramCls) {
    112        if (bldrCls == null) {
    113            throw new IllegalArgumentException("Builder class must not be null.");
    114        }
    115        if (configCls == null) {
    116            throw new IllegalArgumentException("Configuration class must not be null.");
    117        }
    118
    119        builderClass = bldrCls;
    120        reloadingBuilderClass = reloadBldrCls;
    121        configurationClass = configCls;
    122        parameterClasses = initParameterClasses(paramCls);
    123    }
    124
    125    /**
    126     * Configures a newly created builder instance with its initialization parameters. This method is called after a new
    127     * instance was created using reflection. This implementation passes the parameter objects to the builder's
    128     * {@code configure()} method.
    129     *
    130     * @param builder the builder to be initialized
    131     * @param decl the current {@code ConfigurationDeclaration}
    132     * @param params the collection with initialization parameter objects
    133     * @throws Exception if an error occurs
    134     */
    135    protected void configureBuilder(final BasicConfigurationBuilder<? extends Configuration> builder, final ConfigurationDeclaration decl,
    136        final Collection<BuilderParameters> params) throws Exception {
    137        builder.configure(params.toArray(new BuilderParameters[params.size()]));
    138    }
    139
    140    /**
    141     * Creates a new, uninitialized instance of the builder class managed by this provider. This implementation determines
    142     * the builder class to be used by delegating to {@code determineBuilderClass()}. It then calls the constructor
    143     * expecting the configuration class, the map with properties, and the<em>allowFailOnInit</em> flag.
    144     *
    145     * @param decl the current {@code ConfigurationDeclaration}
    146     * @param params initialization parameters for the new builder object
    147     * @return the newly created builder instance
    148     * @throws Exception if an error occurs
    149     */
    150    protected BasicConfigurationBuilder<? extends Configuration> createBuilder(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
    151        throws Exception {
    152        final Class<?> bldCls = ConfigurationUtils.loadClass(determineBuilderClass(decl));
    153        final Class<?> configCls = ConfigurationUtils.loadClass(determineConfigurationClass(decl, params));
    154        final Constructor<?> ctor = bldCls.getConstructor(CTOR_PARAM_TYPES);
    155        // ? extends Configuration is the minimum constraint
    156        @SuppressWarnings("unchecked")
    157        final BasicConfigurationBuilder<? extends Configuration> builder = (BasicConfigurationBuilder<? extends Configuration>) ctor.newInstance(configCls,
    158            null, isAllowFailOnInit(decl));
    159        return builder;
    160    }
    161
    162    /**
    163     * Creates a collection of parameter objects to be used for configuring the builder. This method creates instances of
    164     * the parameter classes passed to the constructor.
    165     *
    166     * @return a collection with parameter objects for the builder
    167     * @throws Exception if an error occurs while creating parameter objects via reflection
    168     */
    169    protected Collection<BuilderParameters> createParameterObjects() throws Exception {
    170        final Collection<BuilderParameters> params = new ArrayList<>(getParameterClasses().size());
    171        for (final String paramcls : getParameterClasses()) {
    172            params.add(createParameterObject(paramcls));
    173        }
    174        return params;
    175    }
    176
    177    /**
    178     * Determines the name of the class to be used for a new builder instance. This implementation selects between the
    179     * normal and the reloading builder class, based on the passed in {@code ConfigurationDeclaration}. If a reloading
    180     * builder is desired, but this provider has no reloading support, an exception is thrown.
    181     *
    182     * @param decl the current {@code ConfigurationDeclaration}
    183     * @return the name of the builder class
    184     * @throws ConfigurationException if the builder class cannot be determined
    185     */
    186    protected String determineBuilderClass(final ConfigurationDeclaration decl) throws ConfigurationException {
    187        if (decl.isReload()) {
    188            if (getReloadingBuilderClass() == null) {
    189                throw new ConfigurationException("No support for reloading for builder class %s", getBuilderClass());
    190            }
    191            return getReloadingBuilderClass();
    192        }
    193        return getBuilderClass();
    194    }
    195
    196    /**
    197     * Determines the name of the configuration class produced by the builder. This method is called when obtaining the
    198     * arguments for invoking the constructor of the builder class. This implementation just returns the pre-configured
    199     * configuration class name. Derived classes may determine this class name dynamically based on the passed in
    200     * parameters.
    201     *
    202     * @param decl the current {@code ConfigurationDeclaration}
    203     * @param params the collection with parameter objects
    204     * @return the name of the builder's result configuration class
    205     * @throws ConfigurationException if an error occurs
    206     */
    207    protected String determineConfigurationClass(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
    208        throws ConfigurationException {
    209        return getConfigurationClass();
    210    }
    211
    212    /**
    213     * Gets the name of the class of the builder created by this provider.
    214     *
    215     * @return the builder class
    216     */
    217    public String getBuilderClass() {
    218        return builderClass;
    219    }
    220
    221    /**
    222     * {@inheritDoc} This implementation delegates to some protected methods to create a new builder instance using
    223     * reflection and to configure it with parameter values defined by the passed in {@code BeanDeclaration}.
    224     */
    225    @Override
    226    public ConfigurationBuilder<? extends Configuration> getConfigurationBuilder(final ConfigurationDeclaration decl) throws ConfigurationException {
    227        try {
    228            final Collection<BuilderParameters> params = createParameterObjects();
    229            initializeParameterObjects(decl, params);
    230            final BasicConfigurationBuilder<? extends Configuration> builder = createBuilder(decl, params);
    231            configureBuilder(builder, decl, params);
    232            return builder;
    233        } catch (final ConfigurationException cex) {
    234            throw cex;
    235        } catch (final Exception ex) {
    236            throw new ConfigurationException(ex);
    237        }
    238    }
    239
    240    /**
    241     * Gets the name of the configuration class created by the builder produced by this provider.
    242     *
    243     * @return the configuration class
    244     */
    245    public String getConfigurationClass() {
    246        return configurationClass;
    247    }
    248
    249    /**
    250     * Gets an unmodifiable collection with the names of parameter classes supported by this provider.
    251     *
    252     * @return the parameter classes
    253     */
    254    public Collection<String> getParameterClasses() {
    255        return parameterClasses;
    256    }
    257
    258    /**
    259     * Gets the name of the class of the builder created by this provider if the reload flag is set. If this method
    260     * returns <strong>null</strong>, reloading builders are not supported by this provider.
    261     *
    262     * @return the reloading builder class
    263     */
    264    public String getReloadingBuilderClass() {
    265        return reloadingBuilderClass;
    266    }
    267
    268    /**
    269     * Passes all parameter objects to the parent {@code CombinedConfigurationBuilder} so that properties already defined
    270     * for the parent builder can be added. This method is called before the parameter objects are initialized from the
    271     * definition configuration. This way properties from the parent builder are inherited, but can be overridden for child
    272     * configurations.
    273     *
    274     * @param decl the current {@code ConfigurationDeclaration}
    275     * @param params the collection with (uninitialized) parameter objects
    276     */
    277    protected void inheritParentBuilderProperties(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params) {
    278        params.forEach(p -> decl.getConfigurationBuilder().initChildBuilderParameters(p));
    279    }
    280
    281    /**
    282     * Initializes the parameter objects with data stored in the current bean declaration. This method is called before the
    283     * newly created builder instance is configured with the parameter objects. It maps attributes of the bean declaration
    284     * to properties of parameter objects. In addition, it invokes the parent {@code CombinedConfigurationBuilder} so that
    285     * the parameters object can inherit properties already defined for this builder.
    286     *
    287     * @param decl the current {@code ConfigurationDeclaration}
    288     * @param params the collection with (uninitialized) parameter objects
    289     * @throws Exception if an error occurs
    290     */
    291    protected void initializeParameterObjects(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params) throws Exception {
    292        inheritParentBuilderProperties(decl, params);
    293        final MultiWrapDynaBean wrapBean = new MultiWrapDynaBean(params);
    294        decl.getConfigurationBuilder().initBean(wrapBean, decl);
    295    }
    296
    297    /**
    298     * Determines the <em>allowFailOnInit</em> flag for the newly created builder based on the given
    299     * {@code ConfigurationDeclaration}. Some combinations of flags in the declaration say that a configuration source is
    300     * optional, but an empty instance should be created if its creation fail.
    301     *
    302     * @param decl the current {@code ConfigurationDeclaration}
    303     * @return the value of the <em>allowFailOnInit</em> flag
    304     */
    305    protected boolean isAllowFailOnInit(final ConfigurationDeclaration decl) {
    306        return decl.isOptional() && decl.isForceCreate();
    307    }
    308}