BaseConfigurationBuilderProvider.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2.builder.combined;
import java.lang.reflect.Constructor;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import org.apache.commons.configuration2.Configuration;
import org.apache.commons.configuration2.ConfigurationUtils;
import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
import org.apache.commons.configuration2.builder.BuilderParameters;
import org.apache.commons.configuration2.builder.ConfigurationBuilder;
import org.apache.commons.configuration2.ex.ConfigurationException;
/**
* <p>
* A fully-functional, reflection-based implementation of the {@code ConfigurationBuilderProvider} interface which can
* deal with the default tags defining configuration sources.
* </p>
* <p>
* An instance of this class is initialized with the names of the {@code ConfigurationBuilder} class used by this
* provider and the concrete {@code Configuration} class. The {@code ConfigurationBuilder} class must be derived from
* {@link BasicConfigurationBuilder}. When asked for the builder object, an instance of the builder class is created and
* initialized from the bean declaration associated with the current configuration source.
* </p>
* <p>
* {@code ConfigurationBuilder} objects are configured using parameter objects. When declaring configuration sources in
* XML it should not be necessary to define the single parameter objects. Rather, simple and complex properties are set
* in the typical way of a bean declaration (i.e. as attributes of the current XML element or as child elements). This
* class creates all supported parameter objects (whose names also must be provided at construction time) and takes care
* that their properties are initialized according to the current bean declaration.
* </p>
* <p>
* The use of reflection to create builder instances allows a generic implementation supporting many concrete builder
* classes. Another reason for this approach is that builder classes are only loaded if actually needed. Some
* specialized {@code Configuration} implementations require specific external dependencies which should not be
* mandatory for the use of {@code CombinedConfigurationBuilder}. Because such classes are lazily loaded, an application
* only has to include the dependencies it actually uses.
* </p>
*
* @since 2.0
*/
public class BaseConfigurationBuilderProvider implements ConfigurationBuilderProvider {
/** The types of the constructor parameters for a basic builder. */
private static final Class<?>[] CTOR_PARAM_TYPES = {Class.class, Map.class, Boolean.TYPE};
/**
* Creates an instance of a parameter class using reflection.
*
* @param paramcls the parameter class
* @return the newly created instance
* @throws Exception if an error occurs
*/
private static BuilderParameters createParameterObject(final String paramcls) throws ReflectiveOperationException {
return (BuilderParameters) ConfigurationUtils.loadClass(paramcls).getConstructor().newInstance();
}
/**
* Creates a new, unmodifiable collection for the parameter classes.
*
* @param paramCls the collection with parameter classes passed to the constructor
* @return the collection to be stored
*/
private static Collection<String> initParameterClasses(final Collection<String> paramCls) {
if (paramCls == null) {
return Collections.emptySet();
}
return Collections.unmodifiableCollection(new ArrayList<>(paramCls));
}
/** The name of the builder class. */
private final String builderClass;
/** The name of a builder class with reloading support. */
private final String reloadingBuilderClass;
/** Stores the name of the configuration class to be created. */
private final String configurationClass;
/** A collection with the names of parameter classes. */
private final Collection<String> parameterClasses;
/**
* Creates a new instance of {@code BaseConfigurationBuilderProvider} and initializes all its properties.
*
* @param bldrCls the name of the builder class (must not be <b>null</b>)
* @param reloadBldrCls the name of a builder class to be used if reloading support is required (<b>null</b> if
* reloading is not supported)
* @param configCls the name of the configuration class (must not be <b>null</b>)
* @param paramCls a collection with the names of parameters classes
* @throws IllegalArgumentException if a required parameter is missing
*/
public BaseConfigurationBuilderProvider(final String bldrCls, final String reloadBldrCls, final String configCls, final Collection<String> paramCls) {
if (bldrCls == null) {
throw new IllegalArgumentException("Builder class must not be null!");
}
if (configCls == null) {
throw new IllegalArgumentException("Configuration class must not be null!");
}
builderClass = bldrCls;
reloadingBuilderClass = reloadBldrCls;
configurationClass = configCls;
parameterClasses = initParameterClasses(paramCls);
}
/**
* Configures a newly created builder instance with its initialization parameters. This method is called after a new
* instance was created using reflection. This implementation passes the parameter objects to the builder's
* {@code configure()} method.
*
* @param builder the builder to be initialized
* @param decl the current {@code ConfigurationDeclaration}
* @param params the collection with initialization parameter objects
* @throws Exception if an error occurs
*/
protected void configureBuilder(final BasicConfigurationBuilder<? extends Configuration> builder, final ConfigurationDeclaration decl,
final Collection<BuilderParameters> params) throws Exception {
builder.configure(params.toArray(new BuilderParameters[params.size()]));
}
/**
* Creates a new, uninitialized instance of the builder class managed by this provider. This implementation determines
* the builder class to be used by delegating to {@code determineBuilderClass()}. It then calls the constructor
* expecting the configuration class, the map with properties, and the<em>allowFailOnInit</em> flag.
*
* @param decl the current {@code ConfigurationDeclaration}
* @param params initialization parameters for the new builder object
* @return the newly created builder instance
* @throws Exception if an error occurs
*/
protected BasicConfigurationBuilder<? extends Configuration> createBuilder(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
throws Exception {
final Class<?> bldCls = ConfigurationUtils.loadClass(determineBuilderClass(decl));
final Class<?> configCls = ConfigurationUtils.loadClass(determineConfigurationClass(decl, params));
final Constructor<?> ctor = bldCls.getConstructor(CTOR_PARAM_TYPES);
// ? extends Configuration is the minimum constraint
@SuppressWarnings("unchecked")
final BasicConfigurationBuilder<? extends Configuration> builder = (BasicConfigurationBuilder<? extends Configuration>) ctor.newInstance(configCls,
null, isAllowFailOnInit(decl));
return builder;
}
/**
* Creates a collection of parameter objects to be used for configuring the builder. This method creates instances of
* the parameter classes passed to the constructor.
*
* @return a collection with parameter objects for the builder
* @throws Exception if an error occurs while creating parameter objects via reflection
*/
protected Collection<BuilderParameters> createParameterObjects() throws Exception {
final Collection<BuilderParameters> params = new ArrayList<>(getParameterClasses().size());
for (final String paramcls : getParameterClasses()) {
params.add(createParameterObject(paramcls));
}
return params;
}
/**
* Determines the name of the class to be used for a new builder instance. This implementation selects between the
* normal and the reloading builder class, based on the passed in {@code ConfigurationDeclaration}. If a reloading
* builder is desired, but this provider has no reloading support, an exception is thrown.
*
* @param decl the current {@code ConfigurationDeclaration}
* @return the name of the builder class
* @throws ConfigurationException if the builder class cannot be determined
*/
protected String determineBuilderClass(final ConfigurationDeclaration decl) throws ConfigurationException {
if (decl.isReload()) {
if (getReloadingBuilderClass() == null) {
throw new ConfigurationException("No support for reloading for builder class " + getBuilderClass());
}
return getReloadingBuilderClass();
}
return getBuilderClass();
}
/**
* Determines the name of the configuration class produced by the builder. This method is called when obtaining the
* arguments for invoking the constructor of the builder class. This implementation just returns the pre-configured
* configuration class name. Derived classes may determine this class name dynamically based on the passed in
* parameters.
*
* @param decl the current {@code ConfigurationDeclaration}
* @param params the collection with parameter objects
* @return the name of the builder's result configuration class
* @throws ConfigurationException if an error occurs
*/
protected String determineConfigurationClass(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
throws ConfigurationException {
return getConfigurationClass();
}
/**
* Gets the name of the class of the builder created by this provider.
*
* @return the builder class
*/
public String getBuilderClass() {
return builderClass;
}
/**
* {@inheritDoc} This implementation delegates to some protected methods to create a new builder instance using
* reflection and to configure it with parameter values defined by the passed in {@code BeanDeclaration}.
*/
@Override
public ConfigurationBuilder<? extends Configuration> getConfigurationBuilder(final ConfigurationDeclaration decl) throws ConfigurationException {
try {
final Collection<BuilderParameters> params = createParameterObjects();
initializeParameterObjects(decl, params);
final BasicConfigurationBuilder<? extends Configuration> builder = createBuilder(decl, params);
configureBuilder(builder, decl, params);
return builder;
} catch (final ConfigurationException cex) {
throw cex;
} catch (final Exception ex) {
throw new ConfigurationException(ex);
}
}
/**
* Gets the name of the configuration class created by the builder produced by this provider.
*
* @return the configuration class
*/
public String getConfigurationClass() {
return configurationClass;
}
/**
* Gets an unmodifiable collection with the names of parameter classes supported by this provider.
*
* @return the parameter classes
*/
public Collection<String> getParameterClasses() {
return parameterClasses;
}
/**
* Gets the name of the class of the builder created by this provider if the reload flag is set. If this method
* returns <b>null</b>, reloading builders are not supported by this provider.
*
* @return the reloading builder class
*/
public String getReloadingBuilderClass() {
return reloadingBuilderClass;
}
/**
* Passes all parameter objects to the parent {@code CombinedConfigurationBuilder} so that properties already defined
* for the parent builder can be added. This method is called before the parameter objects are initialized from the
* definition configuration. This way properties from the parent builder are inherited, but can be overridden for child
* configurations.
*
* @param decl the current {@code ConfigurationDeclaration}
* @param params the collection with (uninitialized) parameter objects
*/
protected void inheritParentBuilderProperties(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params) {
params.forEach(p -> decl.getConfigurationBuilder().initChildBuilderParameters(p));
}
/**
* Initializes the parameter objects with data stored in the current bean declaration. This method is called before the
* newly created builder instance is configured with the parameter objects. It maps attributes of the bean declaration
* to properties of parameter objects. In addition, it invokes the parent {@code CombinedConfigurationBuilder} so that
* the parameters object can inherit properties already defined for this builder.
*
* @param decl the current {@code ConfigurationDeclaration}
* @param params the collection with (uninitialized) parameter objects
* @throws Exception if an error occurs
*/
protected void initializeParameterObjects(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params) throws Exception {
inheritParentBuilderProperties(decl, params);
final MultiWrapDynaBean wrapBean = new MultiWrapDynaBean(params);
decl.getConfigurationBuilder().initBean(wrapBean, decl);
}
/**
* Determines the <em>allowFailOnInit</em> flag for the newly created builder based on the given
* {@code ConfigurationDeclaration}. Some combinations of flags in the declaration say that a configuration source is
* optional, but an empty instance should be created if its creation fail.
*
* @param decl the current {@code ConfigurationDeclaration}
* @return the value of the <em>allowFailOnInit</em> flag
*/
protected boolean isAllowFailOnInit(final ConfigurationDeclaration decl) {
return decl.isOptional() && decl.isForceCreate();
}
}