GuiceInitializerListener.java

/* vim: set ts=2 et sw=2 cindent fo=qroca: */

package com.globant.katari.shindig;

import java.util.List;

import org.apache.commons.lang.Validate;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.ServletContextListener;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;

import com.google.inject.Guice;
import com.google.inject.Injector;
import com.google.inject.Module;
import com.google.inject.Stage;

/** Initializes the guice injector and makes it available in the servlet
 * context.
 *
 * This listener is intended to be used in a spring bean factory, not directly
 * in web.xml.
 *
 * It stores the injector under the name "guice-injector", the same place
 * expected by shindig.
 */
public class GuiceInitializerListener implements ServletContextListener {

  /** The name that the injector is stored in the servlet context.
   */
  public static final String INJECTOR_ATTRIBUTE_NAME = "guice-injector";

  /** The class logger.
   */
  private static Logger log =
    LoggerFactory.getLogger(GuiceInitializerListener.class);

  /** The list of guice modules to initialize the injectors with.
   *
   * This is never null.
   */
  private List<Module> modules;

  /** Creates a listener that initializes guice with the provided modules.
   *
   * @param guiceModules the list of guice modules. It cannot be null.
   */
  public GuiceInitializerListener(final List<Module> guiceModules) {
    Validate.notNull(guiceModules, "The list of modules cannot be null.");
    modules = guiceModules;
  }

  /** Initializes the guice injector with the provided modules, and stores it
   * in the servlet context.
   *
   * @param event The triggered event. It cannot be null.
   */
  public void contextInitialized(final ServletContextEvent event) {
    log.trace("Entering init");

    ServletContext servletContext = event.getServletContext();
    if (servletContext.getAttribute(INJECTOR_ATTRIBUTE_NAME) != null) {
      throw new RuntimeException("There already is an attribute named "
          + INJECTOR_ATTRIBUTE_NAME + " in the servlet context.");
    }
    Injector injector = Guice.createInjector(Stage.PRODUCTION, modules);
    servletContext.setAttribute(INJECTOR_ATTRIBUTE_NAME, injector);
    log.trace("Leaving init");
  }

  /** Called by the container when the context is about to be destroyed.
   *
   * This implementation destroys the guice injector.
   */
  public void contextDestroyed(final ServletContextEvent event) {
    log.trace("Entering destroy");
    ServletContext context = event.getServletContext();
    context.removeAttribute(INJECTOR_ATTRIBUTE_NAME);
    log.trace("Leaving destroy");
  }
}