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Tools to assist in the reading of configuration/preferences files in
various formats
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/*
* 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;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Iterator;
import org.apache.commons.configuration2.event.ConfigurationErrorEvent;
import org.apache.commons.configuration2.event.Event;
import org.apache.commons.configuration2.event.EventListener;
import org.apache.commons.configuration2.event.EventSource;
import org.apache.commons.configuration2.event.EventType;
import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;
import org.apache.commons.configuration2.sync.NoOpSynchronizer;
import org.apache.commons.configuration2.sync.Synchronizer;
import org.apache.commons.configuration2.tree.ExpressionEngine;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* Miscellaneous utility methods for configurations.
*
* @see ConfigurationConverter Utility methods to convert configurations.
*/
public final class ConfigurationUtils {
/** Constant for the name of the clone() method. */
private static final String METHOD_CLONE = "clone";
/**
* An array with interfaces to be implemented by a proxy for an immutable configuration.
*/
private static final Class[] IMMUTABLE_CONFIG_IFCS = {ImmutableConfiguration.class};
/**
* An array with interfaces to be implemented by a proxy for an immutable hierarchical configuration.
*/
private static final Class[] IMMUTABLE_HIERARCHICAL_CONFIG_IFCS = {ImmutableHierarchicalConfiguration.class};
/**
* A dummy event source that is returned by {@code asEventSource()} if a mock object has to be returned. It provides
* empty dummy implementations for all interface methods.
*/
private static final EventSource DUMMY_EVENT_SOURCE = new EventSource() {
@Override
public void addEventListener(final EventType eventType, final EventListener listener) {
// empty
}
@Override
public boolean removeEventListener(final EventType eventType, final EventListener listener) {
return false;
}
};
/** The logger. */
private static final Log LOG = LogFactory.getLog(ConfigurationUtils.class);
/**
*
* Append all properties from the source configuration to the target configuration. Properties in the source
* configuration are appended to the properties with the same key in the target configuration.
*
*
* Note: This method is not able to handle some specifics of configurations derived from
* {@code AbstractConfiguration} (e.g. list delimiters). For a full support of all of these features the {@code copy()}
* method of {@code AbstractConfiguration} should be used. In a future release this method might become deprecated.
*
*
* @param source the source configuration
* @param target the target configuration
* @since 1.1
*/
public static void append(final Configuration source, final Configuration target) {
append((ImmutableConfiguration) source, target);
}
/**
*
* Append all properties from the source configuration to the target configuration. Properties in the source
* configuration are appended to the properties with the same key in the target configuration.
*
*
* Note: This method is not able to handle some specifics of configurations derived from
* {@code AbstractConfiguration} (e.g. list delimiters). For a full support of all of these features the {@code copy()}
* method of {@code AbstractConfiguration} should be used. In a future release this method might become deprecated.
*
*
* @param source the source configuration
* @param target the target configuration
* @since 2.2
*/
public static void append(final ImmutableConfiguration source, final Configuration target) {
source.getKeys().forEachRemaining(key -> target.addProperty(key, source.getProperty(key)));
}
/**
* Casts the specified object to an {@code EventSource} if possible. The boolean argument determines the method's
* behavior if the object does not implement the {@code EventSource} event: if set to false, a
* {@code ConfigurationRuntimeException} is thrown; if set to true, a dummy {@code EventSource} is returned; on
* this object all methods can be called, but they do not have any effect.
*
* @param obj the object to be cast as {@code EventSource}
* @param mockIfUnsupported a flag whether a mock object should be returned if necessary
* @return an {@code EventSource}
* @throws ConfigurationRuntimeException if the object cannot be cast to {@code EventSource} and the mock flag is
* false
* @since 2.0
*/
public static EventSource asEventSource(final Object obj, final boolean mockIfUnsupported) {
if (obj instanceof EventSource) {
return (EventSource) obj;
}
if (!mockIfUnsupported) {
throw new ConfigurationRuntimeException("Cannot cast to EventSource: " + obj);
}
return DUMMY_EVENT_SOURCE;
}
/**
* An internally used helper method for cloning objects. This implementation is not very sophisticated nor efficient.
* Maybe it can be replaced by an implementation from Commons Lang later. The method checks whether the passed in object
* implements the {@code Cloneable} interface. If this is the case, the {@code clone()} method is invoked by reflection.
* Errors that occur during the cloning process are re-thrown as runtime exceptions.
*
* @param obj the object to be cloned
* @return the cloned object
* @throws CloneNotSupportedException if the object cannot be cloned
*/
static Object clone(final Object obj) throws CloneNotSupportedException {
if (obj instanceof Cloneable) {
try {
final Method m = obj.getClass().getMethod(METHOD_CLONE);
return m.invoke(obj);
} catch (final NoSuchMethodException nmex) {
throw new CloneNotSupportedException("No clone() method found for class" + obj.getClass().getName());
} catch (final IllegalAccessException | InvocationTargetException itex) {
throw new ConfigurationRuntimeException(itex);
}
}
throw new CloneNotSupportedException(obj.getClass().getName() + " does not implement Cloneable");
}
/**
* Clones the given configuration object if this is possible. If the passed in configuration object implements the
* {@code Cloneable} interface, its {@code clone()} method will be invoked. Otherwise an exception will be thrown.
*
* @param config the configuration object to be cloned (can be null)
* @return the cloned configuration (null if the argument was null, too)
* @throws ConfigurationRuntimeException if cloning is not supported for this object
* @since 1.3
*/
public static Configuration cloneConfiguration(final Configuration config) throws ConfigurationRuntimeException {
if (config == null) {
return null;
}
try {
return (Configuration) clone(config);
} catch (final CloneNotSupportedException cnex) {
throw new ConfigurationRuntimeException(cnex);
}
}
/**
* Returns a clone of the passed in object if cloning is supported or the object itself if not. This method checks
* whether the passed in object implements the {@code Cloneable} interface. If this is the case, the {@code clone()}
* method is invoked. Otherwise, the object is directly returned. Errors that might occur during reflection calls are
* caught and also cause this method to return the original object.
*
* @param obj the object to be cloned
* @return the result of the cloning attempt
* @since 2.0
*/
public static Object cloneIfPossible(final Object obj) {
try {
return clone(obj);
} catch (final Exception ex) {
return obj;
}
}
/**
* Creates a clone of the specified {@code Synchronizer}. This method can be called by {@code clone()} implementations
* in configuration classes that also need to copy the {@code Synchronizer} object. This method can handle some
* well-known {@code Synchronizer} implementations directly. For other classes, it uses the following algorithm:
*
* - If the class of the {@code Synchronizer} has a standard constructor, a new instance is created using
* reflection.
* - If this is not possible, it is tried whether the object can be cloned.
*
* If all attempts fail, a {@code ConfigurationRuntimeException} is thrown.
*
* @param sync the {@code Synchronizer} object to be cloned
* @return the clone of this {@code Synchronizer}
* @throws ConfigurationRuntimeException if no clone can be created
* @throws IllegalArgumentException if null is passed in
*/
public static Synchronizer cloneSynchronizer(final Synchronizer sync) {
if (sync == null) {
throw new IllegalArgumentException("Synchronizer must not be null!");
}
if (NoOpSynchronizer.INSTANCE == sync) {
return sync;
}
try {
return sync.getClass().getConstructor().newInstance();
} catch (final Exception ex) {
LOG.info("Cannot create new instance of " + sync.getClass());
}
try {
return (Synchronizer) clone(sync);
} catch (final CloneNotSupportedException cnex) {
throw new ConfigurationRuntimeException("Cannot clone Synchronizer " + sync);
}
}
/**
* Converts the passed in configuration to a hierarchical one. If the configuration is already hierarchical, it is
* directly returned. Otherwise all properties are copied into a new hierarchical configuration.
*
* @param conf the configuration to convert
* @return the new hierarchical configuration (the result is null if and only if the passed in configuration is
* null)
* @since 1.3
*/
public static HierarchicalConfiguration convertToHierarchical(final Configuration conf) {
return convertToHierarchical(conf, null);
}
/**
* Converts the passed in {@code Configuration} object to a hierarchical one using the specified
* {@code ExpressionEngine}. This conversion works by adding the keys found in the configuration to a newly created
* hierarchical configuration. When adding new keys to a hierarchical configuration the keys are interpreted by its
* {@code ExpressionEngine}. If they contain special characters (e.g. brackets) that are treated in a special way by the
* default expression engine, it may be necessary using a specific engine that can deal with such characters. Otherwise
* null can be passed in for the {@code ExpressionEngine}; then the default expression engine is used. If the
* passed in configuration is already hierarchical, it is directly returned. (However, the {@code ExpressionEngine} is
* set if it is not null.) Otherwise all properties are copied into a new hierarchical configuration.
*
* @param conf the configuration to convert
* @param engine the {@code ExpressionEngine} for the hierarchical configuration or null for the default
* @return the new hierarchical configuration (the result is null if and only if the passed in configuration is
* null)
* @since 1.6
*/
public static HierarchicalConfiguration convertToHierarchical(final Configuration conf, final ExpressionEngine engine) {
if (conf == null) {
return null;
}
if (conf instanceof HierarchicalConfiguration) {
final HierarchicalConfiguration hc = (HierarchicalConfiguration) conf;
if (engine != null) {
hc.setExpressionEngine(engine);
}
return hc;
}
final BaseHierarchicalConfiguration hc = new BaseHierarchicalConfiguration();
if (engine != null) {
hc.setExpressionEngine(engine);
}
// Per default, a DisabledListDelimiterHandler is set.
// So list delimiters in property values are not an issue.
hc.copy(conf);
return hc;
}
/**
*
* Copy all properties from the source configuration to the target configuration. Properties in the target configuration
* are replaced with the properties with the same key in the source configuration.
*
*
* Note: This method is not able to handle some specifics of configurations derived from
* {@code AbstractConfiguration} (e.g. list delimiters). For a full support of all of these features the {@code copy()}
* method of {@code AbstractConfiguration} should be used. In a future release this method might become deprecated.
*
*
* @param source the source configuration
* @param target the target configuration
* @since 1.1
*/
public static void copy(final Configuration source, final Configuration target) {
copy((ImmutableConfiguration) source, target);
}
/**
*
* Copy all properties from the source configuration to the target configuration. Properties in the target configuration
* are replaced with the properties with the same key in the source configuration.
*
*
* Note: This method is not able to handle some specifics of configurations derived from
* {@code AbstractConfiguration} (e.g. list delimiters). For a full support of all of these features the {@code copy()}
* method of {@code AbstractConfiguration} should be used. In a future release this method might become deprecated.
*
*
* @param source the source configuration
* @param target the target configuration
* @since 2.2
*/
public static void copy(final ImmutableConfiguration source, final Configuration target) {
source.getKeys().forEachRemaining(key -> target.setProperty(key, source.getProperty(key)));
}
/**
* Helper method for creating a proxy for an unmodifiable configuration. The interfaces the proxy should implement are
* passed as argument.
*
* @param ifcs an array with the interface classes the proxy must implement
* @param c the configuration object to be wrapped
* @return a proxy object for an immutable configuration
* @throws NullPointerException if the configuration is null
*/
private static ImmutableConfiguration createUnmodifiableConfiguration(final Class[] ifcs, final Configuration c) {
return (ImmutableConfiguration) Proxy.newProxyInstance(ConfigurationUtils.class.getClassLoader(), ifcs, new ImmutableConfigurationInvocationHandler(c));
}
/**
* Dump the configuration key/value mappings to some ouput stream. This version of the method exists only for backwards
* compatibility reason.
*
* @param configuration the configuration
* @param out the output stream to dump the configuration to
*/
public static void dump(final Configuration configuration, final PrintStream out) {
dump((ImmutableConfiguration) configuration, out);
}
/**
* Dump the configuration key/value mappings to some writer. This version of the method exists only for backwards
* compatibility reason.
*
* @param configuration the configuration
* @param out the writer to dump the configuration to
*/
public static void dump(final Configuration configuration, final PrintWriter out) {
dump((ImmutableConfiguration) configuration, out);
}
/**
* Dump the configuration key/value mappings to some ouput stream.
*
* @param configuration the configuration
* @param out the output stream to dump the configuration to
* @since 2.2
*/
public static void dump(final ImmutableConfiguration configuration, final PrintStream out) {
dump(configuration, new PrintWriter(out));
}
/**
* Dump the configuration key/value mappings to some writer.
*
* @param configuration the configuration
* @param out the writer to dump the configuration to
* @since 2.2
*/
public static void dump(final ImmutableConfiguration configuration, final PrintWriter out) {
for (final Iterator keys = configuration.getKeys(); keys.hasNext();) {
final String key = keys.next();
final Object value = configuration.getProperty(key);
out.print(key);
out.print("=");
out.print(value);
if (keys.hasNext()) {
out.println();
}
}
out.flush();
}
/**
* Enables runtime exceptions for the specified configuration object. This method can be used for configuration
* implementations that may face errors on normal property access, e.g. {@code DatabaseConfiguration} or
* {@code JNDIConfiguration}. Per default such errors are simply logged and then ignored. This implementation will
* register a special {@link EventListener} that throws a runtime exception (namely a
* {@code ConfigurationRuntimeException}) on each received error event.
*
* @param src the configuration, for which runtime exceptions are to be enabled; this configuration must implement
* {@link EventSource}
*/
public static void enableRuntimeExceptions(final Configuration src) {
if (!(src instanceof EventSource)) {
throw new IllegalArgumentException("Configuration must implement EventSource!");
}
((EventSource) src).addEventListener(ConfigurationErrorEvent.ANY, event -> {
// Throw a runtime exception
throw new ConfigurationRuntimeException(event.getCause());
});
}
/**
* Loads the class with the given name. This method is used whenever a class has to be loaded dynamically. It first
* tries the current thread's context class loader. If this fails, the class loader of this class is tried.
*
* @param clsName the name of the class to be loaded
* @return the loaded class
* @throws ClassNotFoundException if the class cannot be resolved
* @since 2.0
*/
public static Class loadClass(final String clsName) throws ClassNotFoundException {
if (LOG.isDebugEnabled()) {
LOG.debug("Loading class " + clsName);
}
final ClassLoader cl = Thread.currentThread().getContextClassLoader();
try {
if (cl != null) {
return cl.loadClass(clsName);
}
} catch (final ClassNotFoundException cnfex) {
LOG.info("Could not load class " + clsName + " using CCL. Falling back to default CL.", cnfex);
}
return ConfigurationUtils.class.getClassLoader().loadClass(clsName);
}
/**
* Loads the class with the specified name re-throwing {@code ClassNotFoundException} exceptions as runtime exceptions.
* This method works like {@link #loadClass(String)}. However, checked exceptions are caught and re-thrown as
* {@code ConfigurationRuntimeException}.
*
* @param clsName the name of the class to be loaded
* @return the loaded class
* @throws ConfigurationRuntimeException if the class cannot be resolved
* @since 2.0
*/
public static Class loadClassNoEx(final String clsName) {
try {
return loadClass(clsName);
} catch (final ClassNotFoundException cnfex) {
throw new ConfigurationRuntimeException("Cannot load class " + clsName, cnfex);
}
}
/**
* Gets a string representation of the key/value mappings of a configuration. This version of the method exists only for
* backwards compatibility reason.
*
* @param configuration the configuration
* @return a string representation of the configuration
*/
public static String toString(final Configuration configuration) {
return toString((ImmutableConfiguration) configuration);
}
/**
* Gets a string representation of the key/value mappings of a configuration.
*
* @param configuration the configuration
* @return a string representation of the configuration
* @since 2.2
*/
public static String toString(final ImmutableConfiguration configuration) {
final StringWriter writer = new StringWriter();
dump(configuration, new PrintWriter(writer));
return writer.toString();
}
/**
* Creates an {@code ImmutableConfiguration} from the given {@code Configuration} object. This method creates a proxy
* object wrapping the original configuration and making it available under the {@code ImmutableConfiguration}
* interface. Through this interface the configuration cannot be manipulated. It is also not possible to cast the
* returned object back to a {@code Configuration} instance to circumvent this protection.
*
* @param c the {@code Configuration} to be wrapped (must not be null)
* @return an {@code ImmutableConfiguration} view on the specified {@code Configuration} object
* @throws NullPointerException if the passed in {@code Configuration} is null
* @since 2.0
*/
public static ImmutableConfiguration unmodifiableConfiguration(final Configuration c) {
return createUnmodifiableConfiguration(IMMUTABLE_CONFIG_IFCS, c);
}
/**
* Creates an {@code ImmutableHierarchicalConfiguration} from the given {@code HierarchicalConfiguration} object. This
* method works exactly like the method with the same name, but it operates on hierarchical configurations.
*
* @param c the {@code HierarchicalConfiguration} to be wrapped (must not be null)
* @return an {@code ImmutableHierarchicalConfiguration} view on the specified {@code HierarchicalConfiguration} object
* @throws NullPointerException if the passed in {@code HierarchicalConfiguration} is null
* @since 2.0
*/
public static ImmutableHierarchicalConfiguration unmodifiableConfiguration(final HierarchicalConfiguration c) {
return (ImmutableHierarchicalConfiguration) createUnmodifiableConfiguration(IMMUTABLE_HIERARCHICAL_CONFIG_IFCS, c);
}
/**
* Private constructor. Prevents instances from being created.
*/
private ConfigurationUtils() {
// to prevent instantiation...
}
}