GuiceExceptionResolver.java

/*****************************************************************************
 * Copyright 2011 Zdenko Vrabel
 *
 * 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 org.zdevra.guice.mvc;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.zdevra.guice.mvc.exceptions.MethodInvokingException;

import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Singleton;
import com.google.inject.name.Named;

/**
 * Lime's Exception resolver implementation which resolves all throwed exceptions from controllers.
 * 
 * For all exceptions is used generally {@link DefaultExceptionHandler}. If you want to handle the
 * exception, just make binding between exception and your handler.
 * 
 * Example of custom exception handling.
 * <pre class="prettypring">
 * public void configureControllers() {
 *    ...
 *    bindException(Custom1Exception.class).toHandler(Custom1ExceptionHandler.class);
 *    bindException(Custom2Exception.class).toHandlerInstance( new Custom2ExceptionHandler() );
 *    ...
 * }
 * </pre>
 * 
 * Exception handling is executed simmilar as catching block. This means if Custom2Exception in the 
 * example will be derived from Custom1Exception, the resolver uses for Custom2 a first registered handler.
 * In this case Custom1ExceptionHandler.
 *
 */
@Singleton
class GuiceExceptionResolver implements ExceptionResolver {

    @Inject
    private Injector injector;
    private final ExceptionHandler defaultHandler;
    private final Collection<ExceptionBind> binds;


    /**
     * Constructor for Guice
     *
     * @param exceptionBinds
     * @param defaultHandler
     */
    @Inject
    public GuiceExceptionResolver(Set<ExceptionBind> exceptionBinds, @Named(ExceptionResolver.DEFAULT_EXCEPTIONHANDLER_NAME) ExceptionHandler defaultHandler) {
        List<ExceptionBind> bindsArray = new ArrayList<ExceptionBind>(exceptionBinds);
        Collections.sort(bindsArray);
        this.binds = Collections.unmodifiableCollection(bindsArray);
        this.defaultHandler = defaultHandler;
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public void handleException(Throwable t, HttpServlet servlet, HttpServletRequest req, HttpServletResponse resp) {
        if (t instanceof MethodInvokingException) {
            t = t.getCause();
        }

        for (ExceptionBind bind : binds) {
            if (bind.getExceptionClass().isInstance(t)) {
                bind.getHandler(injector).handleException(t, servlet, req, resp);
                return;
            }
        }

        defaultHandler.handleException(t, servlet, req, resp);
    }
}