ManagedServletPipeline.java revision b4b7f7209570bd75352eb322825ae79392f03978
1/**
2 * Copyright (C) 2008 Google Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16package com.google.inject.servlet;
17
18import com.google.inject.Binding;
19import com.google.inject.Inject;
20import com.google.inject.Injector;
21import com.google.inject.Singleton;
22import com.google.inject.TypeLiteral;
23import com.google.inject.internal.util.Lists;
24import com.google.inject.internal.util.Maps;
25import com.google.inject.internal.util.Preconditions;
26import com.google.inject.internal.util.Sets;
27import java.io.IOException;
28import java.util.List;
29import java.util.Set;
30import javax.servlet.RequestDispatcher;
31import javax.servlet.ServletContext;
32import javax.servlet.ServletException;
33import javax.servlet.ServletRequest;
34import javax.servlet.ServletResponse;
35import javax.servlet.http.HttpServlet;
36import javax.servlet.http.HttpServletRequest;
37import javax.servlet.http.HttpServletRequestWrapper;
38
39/**
40 * A wrapping dispatcher for servlets, in much the same way as {@link ManagedFilterPipeline} is for
41 * filters.
42 *
43 * @author dhanji@gmail.com (Dhanji R. Prasanna)
44 */
45@Singleton
46class ManagedServletPipeline {
47  private final ServletDefinition[] servletDefinitions;
48  private static final TypeLiteral<ServletDefinition> SERVLET_DEFS =
49      TypeLiteral.get(ServletDefinition.class);
50
51  @Inject
52  public ManagedServletPipeline(Injector injector) {
53    this.servletDefinitions = collectServletDefinitions(injector);
54  }
55
56  boolean hasServletsMapped() {
57    return servletDefinitions.length > 0;
58  }
59
60  /**
61   * Introspects the injector and collects all instances of bound {@code List<ServletDefinition>}
62   * into a master list.
63   *
64   * We have a guarantee that {@link com.google.inject.Injector#getBindings()} returns a map
65   * that preserves insertion order in entry-set iterators.
66   */
67  private ServletDefinition[] collectServletDefinitions(Injector injector) {
68    List<ServletDefinition> servletDefinitions = Lists.newArrayList();
69    for (Binding<ServletDefinition> entry : injector.findBindingsByType(SERVLET_DEFS)) {
70        servletDefinitions.add(entry.getProvider().get());
71    }
72
73    // Copy to a fixed size array for speed.
74    return servletDefinitions.toArray(new ServletDefinition[servletDefinitions.size()]);
75  }
76
77  public void init(ServletContext servletContext, Injector injector) throws ServletException {
78    Set<HttpServlet> initializedSoFar
79        = Sets.newSetFromMap(Maps.<HttpServlet, Boolean>newIdentityHashMap());
80
81    for (ServletDefinition servletDefinition : servletDefinitions) {
82      servletDefinition.init(servletContext, injector, initializedSoFar);
83    }
84  }
85
86  public boolean service(ServletRequest request, ServletResponse response)
87      throws IOException, ServletException {
88
89    //stop at the first matching servlet and service
90    for (ServletDefinition servletDefinition : servletDefinitions) {
91      if (servletDefinition.service(request, response)) {
92        return true;
93      }
94    }
95
96    //there was no match...
97    return false;
98  }
99
100  public void destroy() {
101    Set<HttpServlet> destroyedSoFar
102        = Sets.newSetFromMap(Maps.<HttpServlet, Boolean>newIdentityHashMap());
103    for (ServletDefinition servletDefinition : servletDefinitions) {
104      servletDefinition.destroy(destroyedSoFar);
105    }
106  }
107
108  /**
109   * @return Returns a request dispatcher wrapped with a servlet mapped to
110   * the given path or null if no mapping was found.
111   */
112  RequestDispatcher getRequestDispatcher(String path) {
113    final String newRequestUri = path;
114
115    // TODO(dhanji): check servlet spec to see if the following is legal or not.
116    // Need to strip query string if requested...
117
118    for (final ServletDefinition servletDefinition : servletDefinitions) {
119      if (servletDefinition.shouldServe(path)) {
120        return new RequestDispatcher() {
121          public void forward(ServletRequest servletRequest, ServletResponse servletResponse)
122              throws ServletException, IOException {
123            Preconditions.checkState(!servletResponse.isCommitted(),
124                "Response has been committed--you can only call forward before"
125                + " committing the response (hint: don't flush buffers)");
126
127            // clear buffer before forwarding
128            servletResponse.resetBuffer();
129
130            ServletRequest requestToProcess;
131            if (servletRequest instanceof HttpServletRequest) {
132               requestToProcess = new RequestDispatcherRequestWrapper(servletRequest, newRequestUri);
133            } else {
134              // This should never happen, but instead of throwing an exception
135              // we will allow a happy case pass thru for maximum tolerance to
136              // legacy (and internal) code.
137              requestToProcess = servletRequest;
138            }
139
140            servletRequest.setAttribute(REQUEST_DISPATCHER_REQUEST, Boolean.TRUE);
141
142            // now dispatch to the servlet
143            try {
144              servletDefinition.doService(requestToProcess, servletResponse);
145            } finally {
146              servletRequest.removeAttribute(REQUEST_DISPATCHER_REQUEST);
147            }
148          }
149
150          public void include(ServletRequest servletRequest, ServletResponse servletResponse)
151              throws ServletException, IOException {
152            servletRequest.setAttribute(REQUEST_DISPATCHER_REQUEST, Boolean.TRUE);
153
154            // route to the target servlet
155            try {
156              servletDefinition.doService(servletRequest, servletResponse);
157            } finally {
158              servletRequest.removeAttribute(REQUEST_DISPATCHER_REQUEST);
159            }
160          }
161        };
162      }
163    }
164
165    //otherwise, can't process
166    return null;
167  }
168
169  /**
170   * A Marker constant attribute that when present in the request indicates to Guice servlet that
171   * this request has been generated by a request dispatcher rather than the servlet pipeline.
172   * In accordance with section 8.4.2 of the Servlet 2.4 specification.
173   */
174  public static final String REQUEST_DISPATCHER_REQUEST = "javax.servlet.forward.servlet_path";
175
176  private static class RequestDispatcherRequestWrapper extends HttpServletRequestWrapper {
177    private final String newRequestUri;
178
179    public RequestDispatcherRequestWrapper(ServletRequest servletRequest, String newRequestUri) {
180      super((HttpServletRequest) servletRequest);
181      this.newRequestUri = newRequestUri;
182    }
183
184    @Override
185    public String getRequestURI() {
186      return newRequestUri;
187    }
188  }
189}
190