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Tools to assist in the reading of configuration/preferences files in
various formats
/*
* 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;
/**
*
* A fully-functional, reflection-based implementation of the
* {@code ConfigurationBuilderProvider} interface which can deal with the
* default tags defining configuration sources.
*
*
* 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.
*
*
* {@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.
*
*
* 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.
*
*
* @version $Id: BaseConfigurationBuilderProvider.java 1624601 2014-09-12 18:04:36Z oheger $
* @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
};
/** 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 parameterClasses;
/**
* Creates a new instance of {@code BaseConfigurationBuilderProvider} and
* initializes all its properties.
*
* @param bldrCls the name of the builder class (must not be null)
* @param reloadBldrCls the name of a builder class to be used if reloading
* support is required (null if reloading is not supported)
* @param configCls the name of the configuration class (must not be
* null)
* @param paramCls a collection with the names of parameters classes
* @throws IllegalArgumentException if a required parameter is missing
*/
public BaseConfigurationBuilderProvider(String bldrCls,
String reloadBldrCls, String configCls, Collection 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);
}
/**
* Returns the name of the class of the builder created by this provider.
*
* @return the builder class
*/
public String getBuilderClass()
{
return builderClass;
}
/**
* Returns the name of the class of the builder created by this provider if
* the reload flag is set. If this method returns null, reloading
* builders are not supported by this provider.
*
* @return the reloading builder class
*/
public String getReloadingBuilderClass()
{
return reloadingBuilderClass;
}
/**
* Returns the name of the configuration class created by the builder
* produced by this provider.
*
* @return the configuration class
*/
public String getConfigurationClass()
{
return configurationClass;
}
/**
* Returns an unmodifiable collection with the names of parameter classes
* supported by this provider.
*
* @return the parameter classes
*/
public Collection getParameterClasses()
{
return parameterClasses;
}
/**
* {@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 getConfigurationBuilder(
ConfigurationDeclaration decl) throws ConfigurationException
{
try
{
Collection params = createParameterObjects();
initializeParameterObjects(decl, params);
BasicConfigurationBuilder builder =
createBuilder(decl, params);
configureBuilder(builder, decl, params);
return builder;
}
catch (ConfigurationException cex)
{
throw cex;
}
catch (Exception ex)
{
throw new ConfigurationException(ex);
}
}
/**
* Determines the allowFailOnInit 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 allowFailOnInit flag
*/
protected boolean isAllowFailOnInit(ConfigurationDeclaration decl)
{
return decl.isOptional() && decl.isForceCreate();
}
/**
* 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 createParameterObjects()
throws Exception
{
Collection params =
new ArrayList(
getParameterClasses().size());
for (String paramcls : getParameterClasses())
{
params.add(createParameterObject(paramcls));
}
return params;
}
/**
* 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(ConfigurationDeclaration decl,
Collection params) throws Exception
{
inheritParentBuilderProperties(decl, params);
MultiWrapDynaBean wrapBean = new MultiWrapDynaBean(params);
decl.getConfigurationBuilder().initBean(wrapBean, decl);
}
/**
* 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(
ConfigurationDeclaration decl, Collection params)
{
for (BuilderParameters p : params)
{
decl.getConfigurationBuilder().initChildBuilderParameters(p);
}
}
/**
* 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 theallowFailOnInit 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 createBuilder(
ConfigurationDeclaration decl, Collection params)
throws Exception
{
Class bldCls =
ConfigurationUtils.loadClass(determineBuilderClass(decl));
Class configCls =
ConfigurationUtils.loadClass(determineConfigurationClass(decl,
params));
Constructor ctor = bldCls.getConstructor(CTOR_PARAM_TYPES);
// ? extends Configuration is the minimum constraint
@SuppressWarnings("unchecked")
BasicConfigurationBuilder builder =
(BasicConfigurationBuilder) ctor
.newInstance(configCls, null, isAllowFailOnInit(decl));
return builder;
}
/**
* 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(
BasicConfigurationBuilder builder,
ConfigurationDeclaration decl, Collection params)
throws Exception
{
builder.configure(params.toArray(new BuilderParameters[params.size()]));
}
/**
* 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(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(ConfigurationDeclaration decl,
Collection params) throws ConfigurationException
{
return getConfigurationClass();
}
/**
* 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(String paramcls)
throws Exception
{
Class cls = ConfigurationUtils.loadClass(paramcls);
BuilderParameters p = (BuilderParameters) cls.newInstance();
return p;
}
/**
* 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 initParameterClasses(
Collection paramCls)
{
if (paramCls == null)
{
return Collections.emptySet();
}
else
{
return Collections.unmodifiableCollection(new ArrayList(
paramCls));
}
}
}