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Java example source code file (ManagedFilterPipeline.java)

This example Java source code file (ManagedFilterPipeline.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, filter_defs, filterdefinition, http, httpservletrequest, inject, injector, list, managedfilterpipeline, managedservletpipeline, provider, request, requestdispatcher, response, servlet, servletexception, servletresponse, set, util

The ManagedFilterPipeline.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,
 * 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.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.Provider;
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.Filter;
import javax.servlet.FilterChain;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

/**
 * Central routing/dispatch class handles lifecycle of managed filters, and delegates to the servlet
 * pipeline.
 *
 * @author dhanji@gmail.com (Dhanji R. Prasanna)
 */
@Singleton
class ManagedFilterPipeline implements FilterPipeline{
  private final FilterDefinition[] filterDefinitions;
  private final ManagedServletPipeline servletPipeline;
  private final Provider<ServletContext> servletContext;

  //Unfortunately, we need the injector itself in order to create filters + servlets
  private final Injector injector;

  //Guards a DCL, so needs to be volatile
  private volatile boolean initialized = false;
  private static final TypeLiteral<FilterDefinition> FILTER_DEFS =
      TypeLiteral.get(FilterDefinition.class);

  @Inject
  public ManagedFilterPipeline(Injector injector, ManagedServletPipeline servletPipeline,
      Provider<ServletContext> servletContext) {
    this.injector = injector;
    this.servletPipeline = servletPipeline;
    this.servletContext = servletContext;

    this.filterDefinitions = collectFilterDefinitions(injector);
  }

  /**
   * Introspects the injector and collects all instances of bound {@code List<FilterDefinition>}
   * 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 FilterDefinition[] collectFilterDefinitions(Injector injector) {
    List<FilterDefinition> filterDefinitions = Lists.newArrayList();
    for (Binding<FilterDefinition> entry : injector.findBindingsByType(FILTER_DEFS)) {
      filterDefinitions.add(entry.getProvider().get());
    }
    
    // Copy to a fixed-size array for speed of iteration.
    return filterDefinitions.toArray(new FilterDefinition[filterDefinitions.size()]);
  }

  public synchronized void initPipeline(ServletContext servletContext)
      throws ServletException {

    //double-checked lock, prevents duplicate initialization
    if (initialized)
      return;

    // Used to prevent duplicate initialization.
    Set<Filter> initializedSoFar = Sets.newIdentityHashSet();

    for (FilterDefinition filterDefinition : filterDefinitions) {
      filterDefinition.init(servletContext, injector, initializedSoFar);
    }

    //next, initialize servlets...
    servletPipeline.init(servletContext, injector);

    //everything was ok...
    initialized = true;
  }

  public void dispatch(ServletRequest request, ServletResponse response,
      FilterChain proceedingFilterChain) throws IOException, ServletException {

    //lazy init of filter pipeline (OK by the servlet specification). This is needed
    //in order for us not to force users to create a GuiceServletContextListener subclass.
    if (!initialized) {
      initPipeline(servletContext.get());
    }

    //obtain the servlet pipeline to dispatch against
    new FilterChainInvocation(filterDefinitions, servletPipeline, proceedingFilterChain)
        .doFilter(withDispatcher(request, servletPipeline), response);

  }

  /**
   * Used to create an proxy that dispatches either to the guice-servlet pipeline or the regular
   * pipeline based on uri-path match. This proxy also provides minimal forwarding support.
   *
   * We cannot forward from a web.xml Servlet/JSP to a guice-servlet (because the filter pipeline
   * is not called again). However, we can wrap requests with our own dispatcher to forward the
   * *other* way. web.xml Servlets/JSPs can forward to themselves as per normal.
   *
   * This is not a problem cuz we intend for people to migrate from web.xml to guice-servlet,
   * incrementally, but not the other way around (which, we should actively discourage).
   */
  @SuppressWarnings({ "JavaDoc", "deprecation" })
  private ServletRequest withDispatcher(ServletRequest servletRequest,
      final ManagedServletPipeline servletPipeline) {

    // don't wrap the request if there are no servlets mapped. This prevents us from inserting our
    // wrapper unless it's actually going to be used. This is necessary for compatibility for apps
    // that downcast their HttpServletRequests to a concrete implementation.
    if (!servletPipeline.hasServletsMapped()) {
      return servletRequest;
    }

    HttpServletRequest request = (HttpServletRequest) servletRequest;
    //noinspection OverlyComplexAnonymousInnerClass
    return new HttpServletRequestWrapper(request) {

      @Override
      public RequestDispatcher getRequestDispatcher(String path) {
        final RequestDispatcher dispatcher = servletPipeline.getRequestDispatcher(path);

        return (null != dispatcher) ? dispatcher : super.getRequestDispatcher(path);
      }
    };
  }

  public void destroyPipeline() {
    //destroy servlets first
    servletPipeline.destroy();

    //go down chain and destroy all our filters
    Set<Filter> destroyedSoFar = Sets.newIdentityHashSet();
    for (FilterDefinition filterDefinition : filterDefinitions) {
      filterDefinition.destroy(destroyedSoFar);
    }
  }
}

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