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Java example source code file (FilterDefinition.java)

This example Java source code file (FilterDefinition.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

atomicreference, filter, filterdefinition, http, instancefilterbindingimpl, key, map, providerinstancebinding, request, response, servlet, servletcontext, servletexception, servletmoduletargetvisitor, string, uripatternmatcher, util

The FilterDefinition.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.collect.Iterators;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Scopes;
import com.google.inject.spi.BindingTargetVisitor;
import com.google.inject.spi.ProviderInstanceBinding;
import com.google.inject.spi.ProviderWithExtensionVisitor;

import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.atomic.AtomicReference;

import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;

 * An internal representation of a filter definition against a particular URI pattern.
 * @author dhanji@gmail.com (Dhanji R. Prasanna)
class FilterDefinition implements ProviderWithExtensionVisitor<FilterDefinition> {
  private final Key<? extends Filter> filterKey;
  private final UriPatternMatcher patternMatcher;
  private final Map<String, String> initParams;
  // set only if this was bound to an instance of a Filter.
  private final Filter filterInstance;

  // always set after init is called.
  private final AtomicReference<Filter> filter = new AtomicReference();

  public FilterDefinition(
      Key<? extends Filter> filterKey,
      UriPatternMatcher patternMatcher,
      Map<String, String> initParams,
      Filter filterInstance) {
    this.filterKey = filterKey;
    this.patternMatcher = patternMatcher;
    this.initParams = Collections.unmodifiableMap(new HashMap<String, String>(initParams));
    this.filterInstance = filterInstance;

  public FilterDefinition get() {
    return this;

  public <B, V> V acceptExtensionVisitor(BindingTargetVisitor visitor,
      ProviderInstanceBinding<? extends B> binding) {
    if(visitor instanceof ServletModuleTargetVisitor) {
      if(filterInstance != null) {
        return ((ServletModuleTargetVisitor<B, V>)visitor).visit(
            new InstanceFilterBindingImpl(initParams,
      } else {
        return ((ServletModuleTargetVisitor<B, V>)visitor).visit(
            new LinkedFilterBindingImpl(initParams,
    } else {
      return visitor.visit(binding);

  private boolean shouldFilter(String uri) {
    return uri != null && patternMatcher.matches(uri);

  public void init(final ServletContext servletContext, Injector injector,
      Set<Filter> initializedSoFar) throws ServletException {

    // This absolutely must be a singleton, and so is only initialized once.
    if (!Scopes.isSingleton(injector.getBinding(filterKey))) {
      throw new ServletException("Filters must be bound as singletons. "
        + filterKey + " was not bound in singleton scope.");

    Filter filter = injector.getInstance(filterKey);

    // Only fire init() if this Singleton filter has not already appeared earlier
    // in the filter chain.
    if (initializedSoFar.contains(filter)) {

    //initialize our filter with the configured context params and servlet context
    filter.init(new FilterConfig() {
      public String getFilterName() {
        return filterKey.toString();

      public ServletContext getServletContext() {
        return servletContext;

      public String getInitParameter(String s) {
        return initParams.get(s);

      public Enumeration getInitParameterNames() {
        return Iterators.asEnumeration(initParams.keySet().iterator());


  public void destroy(Set<Filter> destroyedSoFar) {
    // filters are always singletons
    Filter reference = filter.get();

    // Do nothing if this Filter was invalid (usually due to not being scoped
    // properly), or was already destroyed. According to Servlet Spec: it is
    // "out of service", and does not need to be destroyed.
    // Also prevent duplicate destroys to the same singleton that may appear
    // more than once on the filter chain.
    if (null == reference || destroyedSoFar.contains(reference)) {

    try {
    } finally {

  public Filter getFilterIfMatching(HttpServletRequest request) {

    final String path = ServletUtils.getContextRelativePath(request);
    if (shouldFilter(path)) {
      return filter.get();
    } else {
      return null;

  Filter getFilter() {
    return filter.get();

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