SpringBootstrapFilter.java

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

package com.globant.katari.core.web;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.ServletContext;
import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.FilterChain;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

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

/** A filter that delegates all processing to another filter obtained from the
 * spring application context.
 *
 * It dispatches all requests to a spring configured filter defind under the
 * bean named, by default 'katari.moduleFilterProxy' in the web application
 * context.
 *
 * The specific bean name is configured using the 'filterBeanName'
 * initialization parameter.
 */
public final class SpringBootstrapFilter implements Filter {

  /** The serialization version number.
   *
   * This number must change every time a new serialization incompatible change
   * is introduced in the class.
   */
  private static final long serialVersionUID = 20080221;

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

  /** The target filter that this filter delegates all requests.
   *
   * This is null until initialization.
   */
  private Filter delegate = null;

  /** Called by the servlet container to indicate to the filter that it is
   * being placed into service.
   *
   * @param config The filter configuration and initialization parameters.
   * This object is created by the container.
   *
   * @throws ServletException if an error occurs.
   */
  public void init(final FilterConfig config) throws ServletException {
    log.trace("Entering init");
    String beanName = getBeanName(config);
    WebApplicationContext context;
    context = getWebApplicationcontext(config.getServletContext());
    delegate = (Filter) context.getBean(beanName);
    delegate.init(config);
    log.trace("Leaving init");
  }

  /** Called by the servlet container to allow the filter to pre-process the
   * request.
   *
   * It delegates all the requests to a spring configured filter defined under
   * the bean named, by default, 'filterDispatcher'.
   *
   * @param request The HttpServletRequest object that contains the client's
   * request.
   *
   * @param response The HttpServletResponse object that contains the
   * servlet's response
   *
   * @param chain Allows the filter to pass on the request and response to the
   * next entity in the chain. It cannot be null.
   *
   * @throws IOException if an input or output exception occurs.
   *
   * @throws ServletException if another error occurs.
   */
  public void doFilter(final ServletRequest request, final
      ServletResponse response, final FilterChain chain) throws
      ServletException, IOException {
    log.trace("Entering doFilter");
    delegate.doFilter(request, response, chain);
    log.trace("Leaving doFilter");
  }

  /** Called by the web container to indicate to a filter that it is being
   * taken out of service.
   *
   * It passes the message to the delegate.
   */
  public void destroy() {
    delegate.destroy();
  }

  /** Returns the spring web application context.
   *
   * @param context The servlet context. It cannot be null.
   *
   * @return Returns the spring web application context.
   */
  private WebApplicationContext getWebApplicationcontext(final ServletContext
      context) {
    return WebApplicationContextUtils.getWebApplicationContext(context);
  }

  /** Obtains, from the servlet configuation, the name of the spring bean to
   * delegate the requests to.
   *
   * The name of the bean is specified with the filterBeanName init parameter.
   * The bean must implement the Filter interface.
   *
   * @param config The filter configuration. It cannot be null.
   *
   * @return the bean name as specified in the filter configuration, with the
   * 'filterBeanName' parameter. If the bean name was not specified, it returns
   * 'filterContainer'.
   */
  private String getBeanName(final FilterConfig config) {
    String beanName = config.getInitParameter("filterBeanName");
    if (beanName == null) {
      return "katari.moduleFilterProxy";
    } else {
      return beanName;
    }
  }
}