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Java example source code file (ServletDefinition.java)

This example Java source code file (ServletDefinition.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, http, httpservlet, httpservletrequest, httpservletresponse, ioexception, key, map, net, override, request, response, servlet, servletdefinition, servletexception, servletmoduletargetvisitor, string, uripatternmatcher, util

The ServletDefinition.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 static com.google.inject.servlet.ManagedServletPipeline.REQUEST_DISPATCHER_REQUEST;

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.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
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.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

/**
 * An internal representation of a servlet definition mapped to a particular URI pattern. Also
 * performs the request dispatch to that servlet. How nice and OO =)
 *
 * @author dhanji@gmail.com (Dhanji R. Prasanna)
 */
class ServletDefinition implements ProviderWithExtensionVisitor<ServletDefinition> {
  private final Key<? extends HttpServlet> servletKey;
  private final UriPatternMatcher patternMatcher;
  private final Map<String, String> initParams;
  // set only if this was bound using a servlet instance.
  private final HttpServlet servletInstance;

  //always set in init, our servlet is always presumed to be a singleton
  private final AtomicReference<HttpServlet> httpServlet = new AtomicReference();

  public ServletDefinition(
      Key<? extends HttpServlet> servletKey,
      UriPatternMatcher patternMatcher,
      Map<String, String> initParams,
      HttpServlet servletInstance) {
    this.servletKey = servletKey;
    this.patternMatcher = patternMatcher;
    this.initParams = Collections.unmodifiableMap(new HashMap<String, String>(initParams));
    this.servletInstance = servletInstance;
  }

  public ServletDefinition get() {
    return this;
  }

  public <B, V> V acceptExtensionVisitor(BindingTargetVisitor visitor,
      ProviderInstanceBinding<? extends B> binding) {
    if(visitor instanceof ServletModuleTargetVisitor) {
      if(servletInstance != null) {
        return ((ServletModuleTargetVisitor<B, V>)visitor).visit(
            new InstanceServletBindingImpl(initParams,
                servletInstance,
                patternMatcher));
      } else {
        return ((ServletModuleTargetVisitor<B, V>)visitor).visit(
            new LinkedServletBindingImpl(initParams,
                servletKey,
                patternMatcher));
      }
    } else {
      return visitor.visit(binding);
    }
  }

  boolean shouldServe(String uri) {
    return uri != null && patternMatcher.matches(uri);
  }

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

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

    HttpServlet httpServlet = injector.getInstance(servletKey);
    this.httpServlet.set(httpServlet);

    // Only fire init() if we have not appeared before in the filter chain.
    if (initializedSoFar.contains(httpServlet)) {
      return;
    }

    //initialize our servlet with the configured context params and servlet context
    httpServlet.init(new ServletConfig() {
      public String getServletName() {
        return servletKey.toString();
      }

      public ServletContext getServletContext() {
        return servletContext;
      }

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

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

    // Mark as initialized.
    initializedSoFar.add(httpServlet);
  }

  public void destroy(Set<HttpServlet> destroyedSoFar) {
    HttpServlet reference = httpServlet.get();

    // Do nothing if this Servlet was invalid (usually due to not being scoped
    // properly). 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)) {
      return;
    }

    try {
      reference.destroy();
    } finally {
      destroyedSoFar.add(reference);
    }
  }

  /**
   * Wrapper around the service chain to ensure a servlet is servicing what it must and provides it
   * with a wrapped request.
   *
   * @return Returns true if this servlet triggered for the given request. Or false if
   *          guice-servlet should continue dispatching down the servlet pipeline.
   *
   * @throws IOException If thrown by underlying servlet
   * @throws ServletException If thrown by underlying servlet
   */
  public boolean service(ServletRequest servletRequest,
      ServletResponse servletResponse) throws IOException, ServletException {

    final HttpServletRequest request = (HttpServletRequest) servletRequest;
    final String path = ServletUtils.getContextRelativePath(request);

    final boolean serve = shouldServe(path);

    //invocations of the chain end at the first matched servlet
    if (serve) {
      doService(servletRequest, servletResponse);
    }

    //return false if no servlet matched (so we can proceed down to the web.xml servlets)
    return serve;
  }

  /**
   * Utility that delegates to the actual service method of the servlet wrapped with a contextual
   * request (i.e. with correctly computed path info).
   *
   * We need to suppress deprecation coz we use HttpServletRequestWrapper, which implements
   * deprecated API for backwards compatibility.
   */
  void doService(final ServletRequest servletRequest, ServletResponse servletResponse)
      throws ServletException, IOException {

    HttpServletRequest request = new HttpServletRequestWrapper(
        (HttpServletRequest) servletRequest) {
      private boolean pathComputed;
      private String path;

      private boolean pathInfoComputed;
      private String pathInfo;

      @Override
      public String getPathInfo() {
        if (!isPathInfoComputed()) {
          String servletPath = getServletPath();
          int servletPathLength = servletPath.length();
          String requestUri = getRequestURI();
          pathInfo = requestUri.substring(getContextPath().length()).replaceAll("[/]{2,}", "/");
          // See: https://github.com/google/guice/issues/372
          if (pathInfo.startsWith(servletPath)) {
            pathInfo = pathInfo.substring(servletPathLength);
            // Corner case: when servlet path & request path match exactly (without trailing '/'),
            // then pathinfo is null.
            if (pathInfo.isEmpty() && servletPathLength > 0) {
              pathInfo = null;
            } else {
              try {
                pathInfo = new URI(pathInfo).getPath();
              } catch (URISyntaxException e) {
                // ugh, just leave it alone then
              }
            }
          } else {
            pathInfo = null; // we know nothing additional about the URI.
          }
          pathInfoComputed = true;
        }

        return pathInfo;
      }

      // NOTE(dhanji): These two are a bit of a hack to help ensure that request dispatcher-sent
      // requests don't use the same path info that was memoized for the original request.
      // NOTE(iqshum): I don't think this is possible, since the dispatcher-sent request would
      // perform its own wrapping.
      private boolean isPathInfoComputed() {
        return pathInfoComputed && servletRequest.getAttribute(REQUEST_DISPATCHER_REQUEST) == null;
      }

      private boolean isPathComputed() {
        return pathComputed && servletRequest.getAttribute(REQUEST_DISPATCHER_REQUEST) == null;
      }

      @Override
      public String getServletPath() {
        return computePath();
      }

      @Override
      public String getPathTranslated() {
        final String info = getPathInfo();

        return (null == info) ? null : getRealPath(info);
      }

      // Memoizer pattern.
      private String computePath() {
        if (!isPathComputed()) {
          String servletPath = super.getServletPath();
          path = patternMatcher.extractPath(servletPath);
          pathComputed = true;

          if (null == path) {
            path = servletPath;
          }
        }

        return path;
      }
    };

    doServiceImpl(request, (HttpServletResponse) servletResponse);
  }

  private void doServiceImpl(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    GuiceFilter.Context previous = GuiceFilter.localContext.get();
    HttpServletRequest originalRequest
        = (previous != null) ? previous.getOriginalRequest() : request;
    GuiceFilter.localContext.set(new GuiceFilter.Context(originalRequest, request, response));
    try {
      httpServlet.get().service(request, response);
    } finally {
      GuiceFilter.localContext.set(previous);
    }
  }

  String getKey() {
    return servletKey.toString();
  }
}

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