/* Copyright 2005-2006 Tim Fennell
*
* Licensed 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 net.sourceforge.stripes.exception;
import net.sourceforge.stripes.config.BootstrapPropertyResolver;
import net.sourceforge.stripes.config.Configuration;
import net.sourceforge.stripes.controller.AnnotatedClassActionResolver;
import net.sourceforge.stripes.util.Log;
import net.sourceforge.stripes.util.ResolverUtil;
import net.sourceforge.stripes.util.StringUtil;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.reflect.Modifier;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* <p>An alternative implementation of {@link ExceptionHandler} that discovers and automatically
* configures individual {@link AutoExceptionHandler} classes to handle specific types of
* exceptions. This implementation is most useful when ActionBeans may produce many different
* types of exceptions and it is desirable to separate exception handling logic for different
* groups or classes of exceptions. Using this approach multiple AutoExceptionHandlers can be
* configured simultaneously but do not have to be co-located.</p>
*
* <p>Searches for implementations of AutoExceptionHandler using the same mechanism as is used
* to discover ActionBean implementations - a search of the classpath for classes that implement
* the interface. The search requires one parameter, DelegatingExceptionHandler.Packages, which
* should contain a comma separated list of root packages to search for AutoExceptionHandler
* classes. If this parameter is <i>not</i> specified, the DelegatingExceptionHandler will use
* the configuration parameter that is used for discovering ActionBean instances
* (ActionResolver.Packages). The configuration parameter is usually specified as an
* init-param for the Stripes Filter, e.g.:</p>
*
*<pre>
*<init-param>
* <param-name>DelegatingExceptionHandler.Packages</param-name>
* <param-value>com.myco.web,com.myco.shared</param-value>
*</init-param>
*</pre>
*
* <p>When the {@link #handle(Throwable, HttpServletRequest, HttpServletResponse)} is invoked
* the set of AutoExceptionHandlers is examined to find the handler with the most specific
* signature that is capable of handling the exception. If no handler is available to handle the
* exception type supplied then the exception will be rethrown; if the exception is not a
* ServletException it will be wrapped in a StripesServletException before being rethrown.</p>
*
* <p>If it is desirable to ensure that all exceptions are handled simply create an
* AutoExceptionHandler that takes with {@link java.lang.Exception} (preferable) or
* {@link java.lang.Throwable} (this may catch unhandlable errors like OutOfMemoryError).</p>
*
* @author Jeppe Cramon, Tim Fennell
* @since Stripes 1.3
*/
public class DelegatingExceptionHandler extends DefaultExceptionHandler {
/** Log instance for use within in this class. */
private static final Log log = Log.getInstance(DelegatingExceptionHandler.class);
/**
* Configuration key used to lookup the list of packages to scan for auto handlers.
* @since Stripes 1.5
*/
public static final String PACKAGES = "DelegatingExceptionHandler.Packages";
/**
* Looks up the filters as defined in the Configuration and then invokes the
* {@link ResolverUtil} to find implementations of AutoExceptionHandler. Each
* implementation found is then examined and cached by calling
* {@link #addHandler(Class)}
*
* @param configuration the Configuration for this Stripes application
* @throws Exception thrown if any of the discovered handler types cannot be safely
* instantiated
*/
@Override
public void init(Configuration configuration) throws Exception {
super.init(configuration);
// Fetch the AutoExceptionHandler implementations and add them to the cache
Set<Class<? extends AutoExceptionHandler>> handlers = findClasses();
for (Class<? extends AutoExceptionHandler> handler : handlers) {
if (!Modifier.isAbstract(handler.getModifiers())) {
log.debug("Processing class ", handler, " looking for exception handling methods.");
addHandler(handler);
}
}
}
/**
* Helper method to find implementations of AutoExceptionHandler in the packages specified in
* Configuration using the {@link ResolverUtil} class.
*
* @return a set of Class objects that represent subclasses of AutoExceptionHandler
*/
protected Set<Class<? extends AutoExceptionHandler>> findClasses() {
BootstrapPropertyResolver bootstrap = getConfiguration().getBootstrapPropertyResolver();
// Try the config param that is specific to this class
String[] packages = StringUtil.standardSplit(bootstrap.getProperty(PACKAGES));
if (packages == null || packages.length == 0) {
// Config param not found so try autodiscovery
log.info("No config parameter '", PACKAGES, "' found. Trying autodiscovery instead.");
List<Class<? extends AutoExceptionHandler>> classes = bootstrap
.getClassPropertyList(AutoExceptionHandler.class);
if (!classes.isEmpty()) {
return new HashSet<Class<? extends AutoExceptionHandler>>(classes);
}
else {
// Autodiscovery found nothing so resort to looking at the ActionBean packages
log.info("Autodiscovery found no implementations of AutoExceptionHandler. Using ",
"the value of '", AnnotatedClassActionResolver.PACKAGES, "' instead.");
packages = StringUtil.standardSplit(bootstrap
.getProperty(AnnotatedClassActionResolver.PACKAGES));
}
}
if (packages != null && packages.length > 0) {
ResolverUtil<AutoExceptionHandler> resolver = new ResolverUtil<AutoExceptionHandler>();
resolver.findImplementations(AutoExceptionHandler.class, packages);
return resolver.getClasses();
}
else {
return Collections.emptySet();
}
}
}