1 /**
2  * Copyright (C) 2010 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  */
16 
17 package com.google.inject.persist;
18 
19 import com.google.inject.Inject;
20 import com.google.inject.Singleton;
21 
22 import java.io.IOException;
23 
24 import javax.servlet.Filter;
25 import javax.servlet.FilterChain;
26 import javax.servlet.FilterConfig;
27 import javax.servlet.ServletException;
28 import javax.servlet.ServletRequest;
29 import javax.servlet.ServletResponse;
30 
31 /**
32  * Apply this filter to enable the HTTP Request unit of work and to have
33  * guice-persist manage the lifecycle of active units of work.
34  * The filter automatically starts and stops the relevant {@link PersistService}
35  * upon {@link javax.servlet.Filter#init(javax.servlet.FilterConfig)} and
36  * {@link javax.servlet.Filter#destroy()} respectively.
37  *
38  * <p> To be able to use the open session-in-view pattern (i.e. work per request),
39  * register this filter <b>once</b> in your Guice {@code ServletModule}. It is
40  * important that you register this filter before any other filter.
41  *
42  * For multiple providers, you should register this filter once per provider, inside
43  * a private module for each persist module installed (this must be the same private
44  * module where the specific persist module is itself installed).
45  *
46  * <p>
47  * Example configuration:
48  * <pre>{@code
49  *  public class MyModule extends ServletModule {
50  *    public void configureServlets() {
51  *      filter("/*").through(PersistFilter.class);
52  *
53  *      serve("/index.html").with(MyHtmlServlet.class);
54  *      // Etc.
55  *    }
56  *  }
57  * }</pre>
58  * <p>
59  * This filter is thread safe and allows you to create injectors concurrently
60  * and deploy multiple guice-persist modules within the same injector, or even
61  * multiple injectors with persist modules withing the same JVM or web app.
62  * <p>
63  * This filter requires the Guice Servlet extension.
64  *
65  * @author Dhanji R. Prasanna (dhanji@gmail.com)
66  */
67 @Singleton
68 public final class PersistFilter implements Filter {
69   private final UnitOfWork unitOfWork;
70   private final PersistService persistService;
71 
72   @Inject
PersistFilter(UnitOfWork unitOfWork, PersistService persistService)73   public PersistFilter(UnitOfWork unitOfWork, PersistService persistService) {
74     this.unitOfWork = unitOfWork;
75     this.persistService = persistService;
76   }
77 
init(FilterConfig filterConfig)78   public void init(FilterConfig filterConfig) throws ServletException {
79     persistService.start();
80   }
81 
destroy()82   public void destroy() {
83     persistService.stop();
84   }
85 
doFilter(final ServletRequest servletRequest, final ServletResponse servletResponse, final FilterChain filterChain)86   public void doFilter(final ServletRequest servletRequest, final ServletResponse servletResponse,
87       final FilterChain filterChain) throws IOException, ServletException {
88 
89     unitOfWork.begin();
90     try {
91       filterChain.doFilter(servletRequest, servletResponse);
92     } finally {
93       unitOfWork.end();
94     }
95   }
96 }
97