protected String determineResourceUrl(HttpServletRequest request) 
{
		return request.getParameter(RESOURCE_PARAM_NAME);
}

Determine the URL of the target resource of this request.

Default implementation returns the value of the "resource" parameter. Can be overridden in subclasses.

 protected final  void doGet(HttpServletRequest request,
    HttpServletResponse response) throws IOException, ServletException 
{
		// determine URL of resource to include
		String resourceUrl = determineResourceUrl(request);
		if (resourceUrl != null) {
			try {
				doInclude(request, response, resourceUrl);
			}
			catch (ServletException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Failed to include content of resource [" + resourceUrl + "]", ex);
				}
				// Try including default URL if appropriate.
				if (!includeDefaultUrl(request, response)) {
					throw ex;
				}
			}
			catch (IOException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Failed to include content of resource [" + resourceUrl + "]", ex);
				}
				// Try including default URL if appropriate.
				if (!includeDefaultUrl(request, response)) {
					throw ex;
				}
			}
		}
		// no resource URL specified - > try to include default URL.
		else if (!includeDefaultUrl(request, response)) {
			throw new ServletException("No target resource URL found for request");
		}
}

Determine the URL of the target resource and include it.

 protected long getFileTimestamp(String resourceUrl) 
{
		ServletContextResource resource = new ServletContextResource(getServletContext(), resourceUrl);
		try {
			long lastModifiedTime = resource.lastModified();
			if (logger.isDebugEnabled()) {
				logger.debug("Last-modified timestamp of " + resource + " is " + lastModifiedTime);
			}
			return lastModifiedTime;
		}
		catch (IOException ex) {
			logger.warn("Couldn't retrieve last-modified timestamp of [" + resource +
					"] - using ResourceServlet startup time");
			return -1;
		}
}

Return the file timestamp for the given resource.

 protected final long getLastModified(HttpServletRequest request) 
{
		if (this.applyLastModified) {
			String resourceUrl = determineResourceUrl(request);
			if (resourceUrl == null) {
				resourceUrl = this.defaultUrl;
			}
			if (resourceUrl != null) {
				String[] resourceUrls = StringUtils.tokenizeToStringArray(resourceUrl, RESOURCE_URL_DELIMITERS);
				long latestTimestamp = -1;
				for (int i = 0; i <  resourceUrls.length; i++) {
					long timestamp = getFileTimestamp(resourceUrls[i]);
					if (timestamp  > latestTimestamp) {
						latestTimestamp = timestamp;
					}
				}
				return (latestTimestamp  > this.startupTime ? latestTimestamp : this.startupTime);
			}
		}
		return -1;
}

Return the last-modified timestamp of the file that corresponds to the target resource URL (i.e. typically the request ".jsp" file). Will simply return -1 if "applyLastModified" is false (the default).

Returns no last-modified date before the startup time of this servlet, to allow for message resolution etc that influences JSP contents, assuming that those background resources might have changed on restart.

Returns the startup time of this servlet if the file that corresponds to the target resource URL coudln't be resolved (for example, because the WAR is not expanded).

 protected PathMatcher getPathMatcher() 
{
		return new AntPathMatcher();
}

Return a PathMatcher to use for matching the "allowedResources" URL pattern. Default is AntPathMatcher.

 protected  void initServletBean() 
{
		this.pathMatcher = getPathMatcher();
		this.startupTime = System.currentTimeMillis();
}

Remember the startup time, using no last-modified time before it.

 public  void setAllowedResources(String allowedResources) 
{
		this.allowedResources = allowedResources;
}

Set allowed resources as URL pattern, e.g. "/WEB-INF/res/*.jsp", The parameter can be any Ant-style pattern parsable by AntPathMatcher.

 public  void setApplyLastModified(boolean applyLastModified) 
{
		this.applyLastModified = applyLastModified;
}

Set whether to apply the file timestamp of the target resource as last-modified value. Default is "false".

This is mainly intended for JSP targets that don't generate session-specific or database-driven content: Such files can be cached by the browser as long as the last-modified timestamp of the JSP file doesn't change.

This will only work correctly with expanded WAR files that allow access to the file timestamps. Else, the startup time of this servlet is returned.

 public  void setContentType(String contentType) 
{
		this.contentType = contentType;
}

Set the content type of the target resource (typically a JSP). Default is none, which is appropriate when including resources.

For directly accessing resources, for example to leverage this servlet's last-modified support, specify a content type here. Note that a content type header in the target JSP will be ignored when including the resource via a RequestDispatcher include.

 public  void setDefaultUrl(String defaultUrl) 
{
	                                                           	 
		this.defaultUrl = defaultUrl;
}

Set the URL within the current web application from which to include content if the requested path isn't found, or if none is specified in the first place.

If specifying multiple URLs, they will be included one by one to build the response. If last-modified determination is active, the newest timestamp among those files will be used.