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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;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import org.apache.commons.configuration2.ConfigurationUtils;
import org.apache.commons.configuration2.ImmutableConfiguration;
import org.apache.commons.configuration2.Initializable;
import org.apache.commons.configuration2.beanutils.BeanDeclaration;
import org.apache.commons.configuration2.beanutils.BeanHelper;
import org.apache.commons.configuration2.beanutils.ConstructorArg;
import org.apache.commons.configuration2.event.Event;
import org.apache.commons.configuration2.event.EventListener;
import org.apache.commons.configuration2.event.EventListenerList;
import org.apache.commons.configuration2.event.EventListenerRegistrationData;
import org.apache.commons.configuration2.event.EventSource;
import org.apache.commons.configuration2.event.EventType;
import org.apache.commons.configuration2.ex.ConfigurationException;
import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;
import org.apache.commons.configuration2.reloading.ReloadingController;
/**
*
* An implementation of the {@code ConfigurationBuilder} interface which is able
* to create different concrete {@code ImmutableConfiguration} implementations based on
* reflection.
*
*
* When constructing an instance of this class the concrete
* {@code ImmutableConfiguration} implementation class has to be provided. Then
* properties for the new {@code ImmutableConfiguration} instance can be set. The first
* call to {@code getConfiguration()} creates and initializes the new
* {@code ImmutableConfiguration} object. It is cached and returned by subsequent calls.
* This cache - and also the initialization properties set so far - can be
* flushed by calling one of the {@code reset()} methods. That way other
* {@code ImmutableConfiguration} instances with different properties can be created.
*
*
* If the newly created {@code ImmutableConfiguration} object implements the
* {@code Initializable} interface, its {@code initialize()} method is called
* after all initialization properties have been set. This way a concrete
* implementation class can perform arbitrary initialization steps.
*
*
* There are multiple options for setting up a {@code BasicConfigurationBuilder}
* instance:
*
*
* - All initialization properties can be set in one or multiple calls of the
* {@code configure()} method. In each call an arbitrary number of
* {@link BuilderParameters} objects can be passed. The API allows method
* chaining and is intended to be used from Java code.
* - If builder instances are created by other means - e.g. using a dependency
* injection framework -, the fluent API approach may not be suitable. For those
* use cases it is also possible to pass in all initialization parameters as a
* map. The keys of the map have to match initialization properties of the
* {@code ImmutableConfiguration} object to be created, the values are the corresponding
* property values. For instance, the key throwExceptionOnMissing in
* the map will cause the method {@code setThrowExceptionOnMissing()} on the
* {@code ImmutableConfiguration} object to be called with the corresponding value as
* parameter.
*
*
* A builder instance can be constructed with an allowFailOnInit
* flag. If set to true, exceptions during initialization
* of the configuration are ignored; in such a case an empty configuration
* object is returned. A use case for this flag is a scenario in which a
* configuration is optional and created on demand the first time configuration
* data is to be stored. Consider an application that stores user-specific
* configuration data in the user's home directory: When started for the first
* time by a new user there is no configuration file; so it makes sense to
* start with an empty configuration object. On application exit, settings
* can be stored in this object and written to the associated file. Then they
* are available on next application start.
*
*
* This class is thread-safe. Multiple threads can modify initialization
* properties and call {@code getConfiguration()}. However, the intended use
* case is that the builder is configured by a single thread first. Then
* {@code getConfiguration()} can be called concurrently, and it is guaranteed
* that always the same {@code ImmutableConfiguration} instance is returned until the
* builder is reset.
*
*
* @since 2.0
* @param the concrete type of {@code ImmutableConfiguration} objects created by this
* builder
*/
public class BasicConfigurationBuilder implements
ConfigurationBuilder
{
/** The class of the objects produced by this builder instance. */
private final Class resultClass;
/** An object managing the event listeners registered at this builder. */
private final EventListenerList eventListeners;
/** A flag whether exceptions on initializing configurations are allowed. */
private final boolean allowFailOnInit;
/** The map with current initialization parameters. */
private Map parameters;
/** The current bean declaration. */
private BeanDeclaration resultDeclaration;
/** The result object of this builder. */
private volatile T result;
/**
* Creates a new instance of {@code BasicConfigurationBuilder} and
* initializes it with the given result class. No initialization properties
* are set.
*
* @param resCls the result class (must not be null)
* @throws IllegalArgumentException if the result class is null
*/
public BasicConfigurationBuilder(final Class resCls)
{
this(resCls, null);
}
/**
* Creates a new instance of {@code BasicConfigurationBuilder} and
* initializes it with the given result class and an initial set of builder
* parameters. The allowFailOnInit flag is set to
* false.
*
* @param resCls the result class (must not be null)
* @param params a map with initialization parameters
* @throws IllegalArgumentException if the result class is null
*/
public BasicConfigurationBuilder(final Class resCls, final Map params)
{
this(resCls, params, false);
}
/**
* Creates a new instance of {@code BasicConfigurationBuilder} and
* initializes it with the given result class, an initial set of builder
* parameters, and the allowFailOnInit flag. The map with
* parameters may be null, in this case no initialization parameters
* are set.
*
* @param resCls the result class (must not be null)
* @param params a map with initialization parameters
* @param allowFailOnInit a flag whether exceptions on initializing a newly
* created {@code ImmutableConfiguration} object are allowed
* @throws IllegalArgumentException if the result class is null
*/
public BasicConfigurationBuilder(final Class resCls,
final Map params, final boolean allowFailOnInit)
{
if (resCls == null)
{
throw new IllegalArgumentException("Result class must not be null!");
}
resultClass = resCls;
this.allowFailOnInit = allowFailOnInit;
eventListeners = new EventListenerList();
updateParameters(params);
}
/**
* Returns the result class of this builder. The objects produced by this
* builder have the class returned here.
*
* @return the result class of this builder
*/
public Class getResultClass()
{
return resultClass;
}
/**
* Returns the allowFailOnInit flag. See the header comment for
* information about this flag.
*
* @return the allowFailOnInit flag
*/
public boolean isAllowFailOnInit()
{
return allowFailOnInit;
}
/**
* Sets the initialization parameters of this builder. Already existing
* parameters are replaced by the content of the given map.
*
* @param params the new initialization parameters of this builder; can be
* null, then all initialization parameters are removed
* @return a reference to this builder for method chaining
*/
public synchronized BasicConfigurationBuilder setParameters(
final Map params)
{
updateParameters(params);
return this;
}
/**
* Adds the content of the given map to the already existing initialization
* parameters.
*
* @param params the map with additional initialization parameters; may be
* null, then this call has no effect
* @return a reference to this builder for method chaining
*/
public synchronized BasicConfigurationBuilder addParameters(
final Map params)
{
final Map newParams =
new HashMap<>(getParameters());
if (params != null)
{
newParams.putAll(params);
}
updateParameters(newParams);
return this;
}
/**
* Appends the content of the specified {@code BuilderParameters} objects to
* the current initialization parameters. Calling this method multiple times
* will create a union of the parameters provided.
*
* @param params an arbitrary number of objects with builder parameters
* @return a reference to this builder for method chaining
* @throws NullPointerException if a null array is passed
*/
public BasicConfigurationBuilder configure(final BuilderParameters... params)
{
final Map newParams = new HashMap<>();
for (final BuilderParameters p : params)
{
newParams.putAll(p.getParameters());
handleEventListenerProviders(p);
}
return setParameters(newParams);
}
/**
* {@inheritDoc} This implementation creates the result configuration on
* first access. Later invocations return the same object until this builder
* is reset. The double-check idiom for lazy initialization is used (Bloch,
* Effective Java, item 71).
*/
@Override
public T getConfiguration() throws ConfigurationException
{
fireBuilderEvent(new ConfigurationBuilderEvent(this,
ConfigurationBuilderEvent.CONFIGURATION_REQUEST));
T resObj = result;
boolean created = false;
if (resObj == null)
{
synchronized (this)
{
resObj = result;
if (resObj == null)
{
result = resObj = createResult();
created = true;
}
}
}
if (created)
{
fireBuilderEvent(new ConfigurationBuilderResultCreatedEvent(this,
ConfigurationBuilderResultCreatedEvent.RESULT_CREATED,
resObj));
}
return resObj;
}
/**
* {@inheritDoc} This implementation also takes care that the event listener
* is added to the managed configuration object.
*
* @throws IllegalArgumentException if the event type or the listener is
* null
*/
@Override
public void addEventListener(
final EventType eventType, final EventListener listener)
{
installEventListener(eventType, listener);
}
/**
* {@inheritDoc} This implementation also takes care that the event listener
* is removed from the managed configuration object.
*/
@Override
public boolean removeEventListener(
final EventType eventType, final EventListener listener)
{
fetchEventSource().removeEventListener(eventType, listener);
return eventListeners.removeEventListener(eventType, listener);
}
/**
* Clears an existing result object. An invocation of this method causes a
* new {@code ImmutableConfiguration} object to be created the next time
* {@link #getConfiguration()} is called.
*/
public void resetResult()
{
T oldResult;
synchronized (this)
{
oldResult = result;
result = null;
resultDeclaration = null;
}
if (oldResult != null)
{
removeEventListeners(oldResult);
}
fireBuilderEvent(new ConfigurationBuilderEvent(this,
ConfigurationBuilderEvent.RESET));
}
/**
* Removes all initialization parameters of this builder. This method can be
* called if this builder is to be reused for creating result objects with a
* different configuration.
*/
public void resetParameters()
{
setParameters(null);
}
/**
* Resets this builder. This is a convenience method which combines calls to
* {@link #resetResult()} and {@link #resetParameters()}.
*/
public synchronized void reset()
{
resetParameters();
resetResult();
}
/**
* Connects this builder with a {@code ReloadingController}. With this
* method support for reloading can be added to an arbitrary builder object.
* Event listeners are registered at the reloading controller and this
* builder with connect both objects:
*
* - When the reloading controller detects that a reload is required, the
* builder's {@link #resetResult()} method is called; so the managed result
* object is invalidated.
* - When a new result object has been created the controller's reloading
* state is reset, so that new changes can be detected again.
*
*
* @param controller the {@code ReloadingController} to connect to (must not
* be null)
* @throws IllegalArgumentException if the controller is null
*/
public final void connectToReloadingController(
final ReloadingController controller)
{
if (controller == null)
{
throw new IllegalArgumentException(
"ReloadingController must not be null!");
}
ReloadingBuilderSupportListener.connect(this, controller);
}
/**
* Creates a new, initialized result object. This method is called by
* {@code getConfiguration()} if no valid result object exists. This base
* implementation performs two steps:
*
* - {@code createResultInstance()} is called to create a new,
* uninitialized result object.
* - {@code initResultInstance()} is called to process all initialization
* parameters.
*
* It also evaluates the allowFailOnInit flag, i.e. if
* initialization causes an exception and this flag is set, the exception is
* ignored, and the newly created, uninitialized configuration is returned.
* Note that this method is called in a synchronized block.
*
* @return the newly created result object
* @throws ConfigurationException if an error occurs
*/
protected T createResult() throws ConfigurationException
{
final T resObj = createResultInstance();
try
{
initResultInstance(resObj);
}
catch (final ConfigurationException cex)
{
if (!isAllowFailOnInit())
{
throw cex;
}
}
return resObj;
}
/**
* Creates the new, uninitialized result object. This is the first step of
* the process of producing a result object for this builder. This
* implementation uses the {@link BeanHelper} class to create a new object
* based on the {@link BeanDeclaration} returned by
* {@link #getResultDeclaration()}. Note: This method is invoked in a
* synchronized block.
*
* @return the newly created, yet uninitialized result object
* @throws ConfigurationException if an exception occurs
*/
protected T createResultInstance() throws ConfigurationException
{
final Object bean = fetchBeanHelper().createBean(getResultDeclaration());
checkResultInstance(bean);
return getResultClass().cast(bean);
}
/**
* Initializes a newly created result object. This is the second step of the
* process of producing a result object for this builder. This
* implementation uses the {@link BeanHelper} class to initialize the
* object's property based on the {@link BeanDeclaration} returned by
* {@link #getResultDeclaration()}. Note: This method is invoked in a
* synchronized block. This is required because internal state is accessed.
* Sub classes must not call this method without proper synchronization.
*
* @param obj the object to be initialized
* @throws ConfigurationException if an error occurs
*/
protected void initResultInstance(final T obj) throws ConfigurationException
{
fetchBeanHelper().initBean(obj, getResultDeclaration());
registerEventListeners(obj);
handleInitializable(obj);
}
/**
* Returns the {@code BeanDeclaration} that is used to create and initialize
* result objects. The declaration is created on first access (by invoking
* {@link #createResultDeclaration(Map)}) based on the current
* initialization parameters.
*
* @return the {@code BeanDeclaration} for dynamically creating a result
* object
* @throws ConfigurationException if an error occurs
*/
protected final synchronized BeanDeclaration getResultDeclaration()
throws ConfigurationException
{
if (resultDeclaration == null)
{
resultDeclaration = createResultDeclaration(getFilteredParameters());
}
return resultDeclaration;
}
/**
* Returns a (unmodifiable) map with the current initialization parameters
* set for this builder. The map is populated with the parameters set using
* the various configuration options.
*
* @return a map with the current set of initialization parameters
*/
protected final synchronized Map getParameters()
{
if (parameters != null)
{
return parameters;
}
return Collections.emptyMap();
}
/**
* Obtains the {@code BeanHelper} object to be used when dealing with bean
* declarations. This method checks whether this builder was configured with
* a specific {@code BeanHelper} instance. If so, this instance is used.
* Otherwise, the default {@code BeanHelper} is returned.
*
* @return the {@code BeanHelper} to be used
*/
protected final BeanHelper fetchBeanHelper()
{
final BeanHelper helper =
BasicBuilderParameters.fetchBeanHelper(getParameters());
return helper != null ? helper : BeanHelper.INSTANCE;
}
/**
* Creates a new {@code BeanDeclaration} which is used for creating new
* result objects dynamically. This implementation creates a specialized
* {@code BeanDeclaration} object that is initialized from the given map of
* initialization parameters. The {@code BeanDeclaration} must be
* initialized with the result class of this builder, otherwise exceptions
* will be thrown when the result object is created. Note: This method is
* invoked in a synchronized block.
*
* @param params a snapshot of the current initialization parameters
* @return the {@code BeanDeclaration} for creating result objects
* @throws ConfigurationException if an error occurs
*/
protected BeanDeclaration createResultDeclaration(
final Map params) throws ConfigurationException
{
return new BeanDeclaration()
{
@Override
public Map getNestedBeanDeclarations()
{
// no nested beans
return Collections.emptyMap();
}
@Override
public Collection getConstructorArgs()
{
// no constructor arguments
return Collections.emptySet();
}
@Override
public Map getBeanProperties()
{
// the properties are equivalent to the parameters
return params;
}
@Override
public Object getBeanFactoryParameter()
{
return null;
}
@Override
public String getBeanFactoryName()
{
return null;
}
@Override
public String getBeanClassName()
{
return getResultClass().getName();
}
};
}
/**
* Copies all {@code EventListener} objects registered at this builder to
* the specified target configuration builder. This method is intended to be
* used by derived classes which support inheritance of their properties to
* other builder objects.
*
* @param target the target configuration builder (must not be null)
* @throws NullPointerException if the target builder is null
*/
protected synchronized void copyEventListeners(
final BasicConfigurationBuilder target)
{
copyEventListeners(target, eventListeners);
}
/**
* Copies all event listeners in the specified list to the specified target
* configuration builder. This method is intended to be used by derived
* classes which have to deal with managed configuration builders that need
* to be initialized with event listeners.
*
* @param target the target configuration builder (must not be null)
* @param listeners the event listeners to be copied over
* @throws NullPointerException if the target builder is null
*/
protected void copyEventListeners(final BasicConfigurationBuilder target,
final EventListenerList listeners)
{
target.eventListeners.addAll(listeners);
}
/**
* Adds the specified event listener to this object. This method is called
* by {@code addEventListener()}, it does the actual listener registration.
* Because it is final it can be called by sub classes in the constructor if
* there is already the need to register an event listener.
*
* @param eventType the event type object
* @param listener the listener to be registered
* @param the event type
*/
protected final void installEventListener(
final EventType eventType, final EventListener listener)
{
fetchEventSource().addEventListener(eventType, listener);
eventListeners.addEventListener(eventType, listener);
}
/**
* Sends the specified builder event to all registered listeners.
*
* @param event the event to be fired
*/
protected void fireBuilderEvent(final ConfigurationBuilderEvent event)
{
eventListeners.fire(event);
}
/**
* Replaces the current map with parameters by a new one.
*
* @param newParams the map with new parameters (may be null)
*/
private void updateParameters(final Map newParams)
{
final Map map = new HashMap<>();
if (newParams != null)
{
map.putAll(newParams);
}
parameters = Collections.unmodifiableMap(map);
}
/**
* Registers the available event listeners at the given object. This method
* is called for each result object created by the builder.
*
* @param obj the object to initialize
*/
private void registerEventListeners(final T obj)
{
final EventSource evSrc = ConfigurationUtils.asEventSource(obj, true);
for (final EventListenerRegistrationData regData : eventListeners
.getRegistrations())
{
registerListener(evSrc, regData);
}
}
/**
* Removes all available event listeners from the given result object. This
* method is called when the result of this builder is reset. Then the old
* managed configuration should no longer generate events.
*
* @param obj the affected result object
*/
private void removeEventListeners(final T obj)
{
final EventSource evSrc = ConfigurationUtils.asEventSource(obj, true);
for (final EventListenerRegistrationData regData : eventListeners
.getRegistrations())
{
removeListener(evSrc, regData);
}
}
/**
* Returns an {@code EventSource} for the current result object. If there is
* no current result or if it does not extend {@code EventSource}, a dummy
* event source is returned.
*
* @return the {@code EventSource} for the current result object
*/
private EventSource fetchEventSource()
{
return ConfigurationUtils.asEventSource(result, true);
}
/**
* Checks whether the specified parameters object implements the
* {@code EventListenerProvider} interface. If so, the event listeners it
* provides are added to this builder.
*
* @param params the parameters object
*/
private void handleEventListenerProviders(final BuilderParameters params)
{
if (params instanceof EventListenerProvider)
{
eventListeners.addAll(((EventListenerProvider) params)
.getListeners());
}
}
/**
* Checks whether the class of the result configuration is compatible with
* this builder's result class. This is done to ensure that only objects of
* the expected result class are created.
*
* @param inst the result instance to be checked
* @throws ConfigurationRuntimeException if an invalid result class is
* detected
*/
private void checkResultInstance(final Object inst)
{
if (!getResultClass().isInstance(inst))
{
throw new ConfigurationRuntimeException(
"Incompatible result object: " + inst);
}
}
/**
* Returns a map with initialization parameters where all parameters
* starting with the reserved prefix have been filtered out.
*
* @return the filtered parameters map
*/
private Map getFilteredParameters()
{
final Map filteredMap =
new HashMap<>(getParameters());
for (final Iterator it = filteredMap.keySet().iterator(); it
.hasNext();)
{
final String key = it.next();
if (key.startsWith(BuilderParameters.RESERVED_PARAMETER_PREFIX))
{
it.remove();
}
}
return filteredMap;
}
/**
* Performs special initialization of the result object. This method is
* called after parameters have been set on a newly created result instance.
* If supported by the result class, the {@code initialize()} method is now
* called.
*
* @param obj the newly created result object
*/
private void handleInitializable(final T obj)
{
if (obj instanceof Initializable)
{
((Initializable) obj).initialize();
}
}
/**
* Registers an event listener at an event source object.
*
* @param evSrc the event source
* @param regData the registration data object
* @param the type of the event listener
*/
private static void registerListener(final EventSource evSrc,
final EventListenerRegistrationData regData)
{
evSrc.addEventListener(regData.getEventType(), regData.getListener());
}
/**
* Removes an event listener from an event source object.
*
* @param evSrc the event source
* @param regData the registration data object
* @param the type of the event listener
*/
private static void removeListener(final EventSource evSrc,
final EventListenerRegistrationData regData)
{
evSrc.removeEventListener(regData.getEventType(), regData.getListener());
}
}