BuilderConfigurationWrapperFactory.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;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import org.apache.commons.configuration2.ConfigurationUtils;
import org.apache.commons.configuration2.ImmutableConfiguration;
import org.apache.commons.configuration2.event.EventSource;
import org.apache.commons.configuration2.ex.ConfigurationException;
/**
* <p>
* A class that allows the creation of configuration objects wrapping a {@link ConfigurationBuilder}.
* </p>
* <p>
* Using this class special {@code ImmutableConfiguration} proxies can be created that delegate all method invocations
* to another {@code ImmutableConfiguration} obtained from a {@code ConfigurationBuilder}. For instance, if there is a
* configuration {@code c} wrapping the builder {@code builder}, the call {@code c.getString(myKey)} is transformed to
* {@code builder.getConfiguration().getString(myKey)}.
* </p>
* <p>
* There are multiple use cases for such a constellation. One example is that client code can continue working with
* {@code ImmutableConfiguration} objects while under the hood builders are used. Another example is that dynamic
* configurations can be realized in a transparent way: a client holds a single configuration (proxy) object, but the
* underlying builder may return a different data object on each call.
* </p>
*
* @since 2.0
*/
public class BuilderConfigurationWrapperFactory {
/**
* A specialized {@code InvocationHandler} implementation for wrapper configurations. Here the logic of accessing a
* wrapped builder is implemented.
*/
private static final class BuilderConfigurationWrapperInvocationHandler implements InvocationHandler {
/** The wrapped builder. */
private final ConfigurationBuilder<? extends ImmutableConfiguration> builder;
/** The level of {@code EventSource} support. */
private final EventSourceSupport eventSourceSupport;
/**
* Creates a new instance of {@code BuilderConfigurationWrapperInvocationHandler}.
*
* @param wrappedBuilder the wrapped builder
* @param evSrcSupport the level of {@code EventSource} support
*/
public BuilderConfigurationWrapperInvocationHandler(final ConfigurationBuilder<? extends ImmutableConfiguration> wrappedBuilder,
final EventSourceSupport evSrcSupport) {
builder = wrappedBuilder;
eventSourceSupport = evSrcSupport;
}
/**
* Handles a method invocation on the associated builder's configuration object.
*
* @param method the method to be invoked
* @param args method arguments
* @return the return value of the method
* @throws Exception if an error occurs
*/
private Object handleConfigurationInvocation(final Method method, final Object[] args) throws ReflectiveOperationException, ConfigurationException {
return method.invoke(builder.getConfiguration(), args);
}
/**
* Handles a method invocation on the {@code EventSource} interface. This method evaluates the current
* {@code EventSourceSupport} object in order to find the appropriate target for the invocation.
*
* @param method the method to be invoked
* @param args method arguments
* @return the return value of the method
* @throws ReflectiveOperationException if an error occurs
*/
private Object handleEventSourceInvocation(final Method method, final Object... args) throws ReflectiveOperationException {
return method.invoke(EventSourceSupport.DUMMY == eventSourceSupport ? ConfigurationUtils.asEventSource(this, true) : builder, args);
}
/**
* Handles method invocations. This implementation handles methods of two different interfaces:
* <ul>
* <li>Methods from the {@code EventSource} interface are handled according to the current support level.</li>
* <li>Other method calls are delegated to the builder's configuration object.</li>
* </ul>
*
* @param proxy the proxy object
* @param method the method to be invoked
* @param args method arguments
* @return the return value of the method
* @throws ReflectiveOperationException if an error occurs
* @throws ConfigurationException if an error occurs
*/
@Override
public Object invoke(final Object proxy, final Method method, final Object[] args) throws ReflectiveOperationException, ConfigurationException {
return EventSource.class.equals(method.getDeclaringClass()) ? handleEventSourceInvocation(method, args)
: handleConfigurationInvocation(method, args);
}
}
/**
* <p>
* An enumeration class with different options for supporting the {@code EventSource} interface in generated
* {@code ImmutableConfiguration} proxies.
* </p>
* <p>
* Using literals of this class it is possible to specify that a {@code ImmutableConfiguration} object returned by
* {@code BuilderConfigurationWrapperFactory} also implements the {@code EventSource} interface and how this
* implementation should work. See the documentation of the single constants for more details.
* </p>
*/
public enum EventSourceSupport {
/**
* No support of the {@code EventSource} interface. If this option is set, {@code ImmutableConfiguration} objects
* generated by {@code BuilderConfigurationWrapperFactory} do not implement the {@code EventSource} interface.
*/
NONE,
/**
* Dummy support of the {@code EventSource} interface. This option causes {@code ImmutableConfiguration} objects
* generated by {@code BuilderConfigurationWrapperFactory} to implement the {@code EventSource} interface, however, this
* implementation consists only of empty dummy methods without real functionality.
*/
DUMMY,
/**
* {@code EventSource} support is implemented by delegating to the associated {@code ConfigurationBuilder} object. If
* this option is used, generated {@code ImmutableConfiguration} objects provide a fully functional implementation of
* {@code EventSource} by delegating to the builder. Because the {@code ConfigurationBuilder} interface extends
* {@code EventSource} this delegation is always possible.
*/
BUILDER
}
/**
* Creates a {@code ImmutableConfiguration} object which wraps the specified {@code ConfigurationBuilder}. Each access
* of the configuration is delegated to a corresponding call on the {@code ImmutableConfiguration} object managed by the
* builder. This is a convenience method which allows creating wrapper configurations without having to instantiate this
* class.
*
* @param <T> the type of the configuration objects returned by this method
* @param ifcClass the class of the configuration objects returned by this method; this must be an interface class and
* must not be <b>null</b>
* @param builder the wrapped {@code ConfigurationBuilder} (must not be <b>null</b>)
* @param evSrcSupport the level of {@code EventSource} support
* @return the wrapper configuration
* @throws IllegalArgumentException if a required parameter is missing
* @throws org.apache.commons.configuration2.ex.ConfigurationRuntimeException if an error occurs when creating the
* result {@code ImmutableConfiguration}
*/
public static <T extends ImmutableConfiguration> T createBuilderConfigurationWrapper(final Class<T> ifcClass,
final ConfigurationBuilder<? extends T> builder, final EventSourceSupport evSrcSupport) {
if (ifcClass == null) {
throw new IllegalArgumentException("Interface class must not be null!");
}
if (builder == null) {
throw new IllegalArgumentException("Builder must not be null!");
}
return ifcClass.cast(Proxy.newProxyInstance(BuilderConfigurationWrapperFactory.class.getClassLoader(), getSupportedInterfaces(ifcClass, evSrcSupport),
new BuilderConfigurationWrapperInvocationHandler(builder, evSrcSupport)));
}
/**
* Gets an array with the classes the generated proxy has to support.
*
* @param ifcClass the class of the configuration objects returned by this method; this must be an interface class and
* must not be <b>null</b>
* @param evSrcSupport the level of {@code EventSource} support
* @return an array with the interface classes to implement
*/
private static Class<?>[] getSupportedInterfaces(final Class<?> ifcClass, final EventSourceSupport evSrcSupport) {
return EventSourceSupport.NONE == evSrcSupport ? new Class<?>[] {ifcClass} : new Class<?>[] {EventSource.class, ifcClass};
}
/** The current {@code EventSourceSupport} value. */
private final EventSourceSupport eventSourceSupport;
/**
* Creates a new instance of {@code BuilderConfigurationWrapperFactory} setting the default {@code EventSourceSupport}
* <em>NONE</em>.
*/
public BuilderConfigurationWrapperFactory() {
this(EventSourceSupport.NONE);
}
/**
* Creates a new instance of {@code BuilderConfigurationWrapperFactory} and sets the property for supporting the
* {@code EventSource} interface.
*
* @param evSrcSupport the level of {@code EventSource} support
*/
public BuilderConfigurationWrapperFactory(final EventSourceSupport evSrcSupport) {
eventSourceSupport = evSrcSupport;
}
/**
* Creates a wrapper {@code ImmutableConfiguration} on top of the specified {@code ConfigurationBuilder}. This
* implementation delegates to
* {@link #createBuilderConfigurationWrapper(Class, ConfigurationBuilder, EventSourceSupport)} .
*
* @param <T> the type of the configuration objects returned by this method
* @param ifcClass the class of the configuration objects returned by this method; this must be an interface class and
* must not be <b>null</b>
* @param builder the wrapped {@code ConfigurationBuilder} (must not be <b>null</b>)
* @return the wrapper configuration
* @throws IllegalArgumentException if a required parameter is missing
* @throws org.apache.commons.configuration2.ex.ConfigurationRuntimeException if an error occurs when creating the
* result {@code ImmutableConfiguration}
*/
public <T extends ImmutableConfiguration> T createBuilderConfigurationWrapper(final Class<T> ifcClass, final ConfigurationBuilder<? extends T> builder) {
return createBuilderConfigurationWrapper(ifcClass, builder, getEventSourceSupport());
}
/**
* Gets the level of {@code EventSource} support used when generating {@code ImmutableConfiguration} objects.
*
* @return the level of {@code EventSource} support
*/
public EventSourceSupport getEventSourceSupport() {
return eventSourceSupport;
}
}