Java tutorial
/** * Copyright (C) 2008 Google Inc. * * 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 com.google.inject.servlet; import com.google.common.base.Preconditions; import com.google.common.collect.Lists; import com.google.common.collect.Sets; import com.google.inject.Binding; import com.google.inject.Inject; import com.google.inject.Injector; import com.google.inject.Singleton; import com.google.inject.TypeLiteral; import java.io.IOException; import java.util.List; import java.util.Set; import javax.servlet.RequestDispatcher; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletRequestWrapper; /** * A wrapping dispatcher for servlets, in much the same way as {@link ManagedFilterPipeline} is for * filters. * * @author dhanji@gmail.com (Dhanji R. Prasanna) */ @Singleton class ManagedServletPipeline { private final ServletDefinition[] servletDefinitions; private static final TypeLiteral<ServletDefinition> SERVLET_DEFS = TypeLiteral.get(ServletDefinition.class); @Inject public ManagedServletPipeline(Injector injector) { this.servletDefinitions = collectServletDefinitions(injector); } boolean hasServletsMapped() { return servletDefinitions.length > 0; } /** * Introspects the injector and collects all instances of bound {@code List<ServletDefinition>} * into a master list. * * We have a guarantee that {@link com.google.inject.Injector#getBindings()} returns a map * that preserves insertion order in entry-set iterators. */ private ServletDefinition[] collectServletDefinitions(Injector injector) { List<ServletDefinition> servletDefinitions = Lists.newArrayList(); for (Binding<ServletDefinition> entry : injector.findBindingsByType(SERVLET_DEFS)) { servletDefinitions.add(entry.getProvider().get()); } // Copy to a fixed size array for speed. return servletDefinitions.toArray(new ServletDefinition[servletDefinitions.size()]); } public void init(ServletContext servletContext, Injector injector) throws ServletException { Set<HttpServlet> initializedSoFar = Sets.newIdentityHashSet(); for (ServletDefinition servletDefinition : servletDefinitions) { servletDefinition.init(servletContext, injector, initializedSoFar); } } public boolean service(ServletRequest request, ServletResponse response) throws IOException, ServletException { //stop at the first matching servlet and service for (ServletDefinition servletDefinition : servletDefinitions) { if (servletDefinition.service(request, response)) { return true; } } //there was no match... return false; } public void destroy() { Set<HttpServlet> destroyedSoFar = Sets.newIdentityHashSet(); for (ServletDefinition servletDefinition : servletDefinitions) { servletDefinition.destroy(destroyedSoFar); } } /** * @return Returns a request dispatcher wrapped with a servlet mapped to * the given path or null if no mapping was found. */ RequestDispatcher getRequestDispatcher(String path) { final String newRequestUri = path; // TODO(dhanji): check servlet spec to see if the following is legal or not. // Need to strip query string if requested... for (final ServletDefinition servletDefinition : servletDefinitions) { if (servletDefinition.shouldServe(path)) { return new RequestDispatcher() { public void forward(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { Preconditions.checkState(!servletResponse.isCommitted(), "Response has been committed--you can only call forward before" + " committing the response (hint: don't flush buffers)"); // clear buffer before forwarding servletResponse.resetBuffer(); ServletRequest requestToProcess; if (servletRequest instanceof HttpServletRequest) { requestToProcess = new RequestDispatcherRequestWrapper(servletRequest, newRequestUri); } else { // This should never happen, but instead of throwing an exception // we will allow a happy case pass thru for maximum tolerance to // legacy (and internal) code. requestToProcess = servletRequest; } // now dispatch to the servlet doServiceImpl(servletDefinition, requestToProcess, servletResponse); } public void include(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { // route to the target servlet doServiceImpl(servletDefinition, servletRequest, servletResponse); } private void doServiceImpl(ServletDefinition servletDefinition, ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { servletRequest.setAttribute(REQUEST_DISPATCHER_REQUEST, Boolean.TRUE); try { servletDefinition.doService(servletRequest, servletResponse); } finally { servletRequest.removeAttribute(REQUEST_DISPATCHER_REQUEST); } } }; } } //otherwise, can't process return null; } /** * A Marker constant attribute that when present in the request indicates to Guice servlet that * this request has been generated by a request dispatcher rather than the servlet pipeline. * In accordance with section 8.4.2 of the Servlet 2.4 specification. */ public static final String REQUEST_DISPATCHER_REQUEST = "javax.servlet.forward.servlet_path"; private static class RequestDispatcherRequestWrapper extends HttpServletRequestWrapper { private final String newRequestUri; public RequestDispatcherRequestWrapper(ServletRequest servletRequest, String newRequestUri) { super((HttpServletRequest) servletRequest); this.newRequestUri = newRequestUri; } @Override public String getRequestURI() { return newRequestUri; } } }