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Java example source code file (ManagedServletPipeline.java)

This example Java source code file (ManagedServletPipeline.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

binding, http, httpservletrequest, ioexception, list, managedservletpipeline, override, request, requestdispatcherrequestwrapper, response, servlet, servletdefinition, servletexception, servletrequest, servletresponse, set, string, stringbuffer, util

The ManagedServletPipeline.java Java example source code

 * 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,
 * 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)
class ManagedServletPipeline {
  private final ServletDefinition[] servletDefinitions;
  private static final TypeLiteral<ServletDefinition> SERVLET_DEFS =

  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)) {

    // 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) {

   * @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 {
                "Response has been committed--you can only call forward before"
                + " committing the response (hint: don't flush buffers)");

            // clear buffer before forwarding

            ServletRequest requestToProcess;
            if (servletRequest instanceof HttpServletRequest) {
               requestToProcess = wrapRequest((HttpServletRequest)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 {

    //otherwise, can't process
    return null;

  // visible for testing
  static HttpServletRequest wrapRequest(HttpServletRequest request, String newUri) {
    return new RequestDispatcherRequestWrapper(request, newUri);

   * 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(HttpServletRequest servletRequest, String newRequestUri) {
      this.newRequestUri = newRequestUri;

    public String getRequestURI() {
      return newRequestUri;

    public StringBuffer getRequestURL() {
      StringBuffer url = new StringBuffer();
      String scheme = getScheme();
      int port = getServerPort();

      // port might be -1 in some cases (see java.net.URL.getPort)
      if (port > 0 &&
          (("http".equals(scheme) && (port != 80)) ||
           ("https".equals(scheme) && (port != 443)))) {

      return (url);

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