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Java example source code file (FilterChainInvocation.java)

This example Java source code file (FilterChainInvocation.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

filter, filterchain, filterchaininvocation, filterdefinition, http, httpservletrequest, httpservletresponse, ioexception, managedservletpipeline, request, response, servlet, servlet_internal_methods, servletexception, set, stacktraceelement, string, throwable, util

The FilterChainInvocation.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.base.Throwables;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;

import java.io.IOException;
import java.util.List;
import java.util.Set;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * A Filter chain impl which basically passes itself to the "current" filter and iterates the chain
 * on {@code doFilter()}. Modeled on something similar in Apache Tomcat.
 *
 * Following this, it attempts to dispatch to guice-servlet's registered servlets using the
 * ManagedServletPipeline.
 *
 * And the end, it proceeds to the web.xml (default) servlet filter chain, if needed.
 *
 * @author Dhanji R. Prasanna
 * @since 1.0
 */
class FilterChainInvocation implements FilterChain {
  
  private static final Set<String> SERVLET_INTERNAL_METHODS = ImmutableSet.of(
      FilterChainInvocation.class.getName() + ".doFilter");
  
  private final FilterDefinition[] filterDefinitions;
  private final FilterChain proceedingChain;
  private final ManagedServletPipeline servletPipeline;

  //state variable tracks current link in filterchain
  private int index = -1;
  // whether or not we've caught an exception & cleaned up stack traces
  private boolean cleanedStacks = false;

  public FilterChainInvocation(FilterDefinition[] filterDefinitions,
      ManagedServletPipeline servletPipeline, FilterChain proceedingChain) {

    this.filterDefinitions = filterDefinitions;
    this.servletPipeline = servletPipeline;
    this.proceedingChain = proceedingChain;
  }

  public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse)
      throws IOException, ServletException {
    GuiceFilter.Context previous = GuiceFilter.localContext.get();
    HttpServletRequest request = (HttpServletRequest) servletRequest;
    HttpServletResponse response = (HttpServletResponse) servletResponse;
    HttpServletRequest originalRequest
        = (previous != null) ? previous.getOriginalRequest() : request;
    GuiceFilter.localContext.set(new GuiceFilter.Context(originalRequest, request, response));
    try {
      Filter filter = findNextFilter(request);
      if (filter != null) {
        // call to the filter, which can either consume the request or
        // recurse back into this method. (in which case we will go to find the next filter,
        // or dispatch to the servlet if no more filters are left)
        filter.doFilter(servletRequest, servletResponse, this);
      } else {
        //we've reached the end of the filterchain, let's try to dispatch to a servlet
        final boolean serviced = servletPipeline.service(servletRequest, servletResponse);

        //dispatch to the normal filter chain only if one of our servlets did not match
        if (!serviced) {
          proceedingChain.doFilter(servletRequest, servletResponse);
        }
      }
    } catch (Throwable t) {
      // Only clean on the first pass through -- one exception deep in a filter
      // will propogate upward & hit this catch clause multiple times.  We don't
      // want to iterate through the stack elements for every filter.
      if (!cleanedStacks) {
        cleanedStacks = true;
        pruneStacktrace(t);
      }
      Throwables.propagateIfInstanceOf(t, ServletException.class);
      Throwables.propagateIfInstanceOf(t, IOException.class);
      throw Throwables.propagate(t);
    } finally {
      GuiceFilter.localContext.set(previous);
    }
  }

  /**
   * Iterates over the remaining filter definitions.
   * Returns the first applicable filter, or null if none apply.
   */
  private Filter findNextFilter(HttpServletRequest request) {
    while (++index < filterDefinitions.length) {
      Filter filter = filterDefinitions[index].getFilterIfMatching(request);
      if (filter != null) {
        return filter;
      }
    }
    return null;
  }
  
  /**
   * Removes stacktrace elements related to AOP internal mechanics from the
   * throwable's stack trace and any causes it may have.
   */
  private void pruneStacktrace(Throwable throwable) {
    for (Throwable t = throwable; t != null; t = t.getCause()) {
      StackTraceElement[] stackTrace = t.getStackTrace();
      List<StackTraceElement> pruned = Lists.newArrayList();
      for (StackTraceElement element : stackTrace) {
        String name = element.getClassName() + "." + element.getMethodName();
        if (!SERVLET_INTERNAL_METHODS.contains(name)) {
          pruned.add(element);
        }
      }
      t.setStackTrace(pruned.toArray(new StackTraceElement[pruned.size()]));
    }
  }
}

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