/*
* Copyright 2002-2008 the original author or authors.
*
* 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 org.springframework.web.servlet;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.PathMatcher;
import org.springframework.util.StringUtils;
import org.springframework.web.context.support.ServletContextResource;
/**
* Simple servlet that can expose an internal resource, including a
* default URL if the specified resource is not found. An alternative,
* for example, to trying and catching exceptions when using JSP include.
*
* <p>A further usage of this servlet is the ability to apply last-modified
* timestamps to quasi-static resources (typically JSPs). This can happen
* as bridge to parameter-specified resources, or as proxy for a specific
* target resource (or a list of specific target resources to combine).
*
* <p>A typical usage would map a URL like "/ResourceServlet" onto an instance
* of this servlet, and use the "JSP include" action to include this URL,
* with the "resource" parameter indicating the actual target path in the WAR.
*
* <p>The <code>defaultUrl</code> property can be set to the internal
* resource path of a default URL, to be rendered when the target resource
* is not found or not specified in the first place.
*
* <p>The "resource" parameter and the <code>defaultUrl</code> property can
* also specify a list of target resources to combine. Those resources 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.
*
* <p>The <code>allowedResources</code> property can be set to a URL
* pattern of resources that should be available via this servlet.
* If not set, any target resource can be requested, including resources
* in the WEB-INF directory!
*
* <p>If using this servlet for direct access rather than via includes,
* the <code>contentType</code> property should be specified to apply a
* proper content type. Note that a content type header in the target JSP will
* be ignored when including the resource via a RequestDispatcher include.
*
* <p>To apply last-modified timestamps for the target resource, set the
* <code>applyLastModified</code> property to true. This servlet will then
* return the file timestamp of the target resource as last-modified value,
* falling back to the startup time of this servlet if not retrievable.
*
* <p>Note that applying the last-modified timestamp in the above fashion
* just makes sense if the target resource does not generate content that
* depends on the HttpSession or cookies; it is just allowed to evaluate
* request parameters.
*
* <p>A typical case for such last-modified usage is a JSP that just makes
* minimal usage of basic means like includes or message resolution to
* build quasi-static content. Regenerating such content on every request
* is unnecessary; it can be cached as long as the file hasn't changed.
*
* <p>Note that this servlet will apply the last-modified timestamp if you
* tell it to do so: It's your decision whether the content of the target
* resource can be cached in such a fashion. Typical use cases are helper
* resources that are not fronted by a controller, like JavaScript files
* that are generated by a JSP (without depending on the HttpSession).
*
* @author Juergen Hoeller
* @author Rod Johnson
* @see #setDefaultUrl
* @see #setAllowedResources
* @see #setApplyLastModified
*/
public class ResourceServlet extends HttpServletBean {
/**
* Any number of these characters are considered delimiters
* between multiple resource paths in a single String value.
*/
public static final String RESOURCE_URL_DELIMITERS = ",; \t\n";
/**
* Name of the parameter that must contain the actual resource path.
*/
public static final String RESOURCE_PARAM_NAME = "resource";
private String defaultUrl;
private String allowedResources;
private String contentType;
private boolean applyLastModified = false;
private PathMatcher pathMatcher;
private long startupTime;
/**
* 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.
* <p>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.
* @see #setApplyLastModified
*/
public void setDefaultUrl(String defaultUrl) {
this.defaultUrl = defaultUrl;
}
/**
* Set allowed resources as URL pattern, e.g. "/WEB-INF/res/*.jsp",
* The parameter can be any Ant-style pattern parsable by AntPathMatcher.
* @see org.springframework.util.AntPathMatcher
*/
public void setAllowedResources(String allowedResources) {
this.allowedResources = allowedResources;
}
/**
* Set the content type of the target resource (typically a JSP).
* Default is none, which is appropriate when including resources.
* <p>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 setContentType(String contentType) {
this.contentType = contentType;
}
/**
* Set whether to apply the file timestamp of the target resource
* as last-modified value. Default is "false".
* <p>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.
* <p>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 setApplyLastModified(boolean applyLastModified) {
this.applyLastModified = applyLastModified;
}
/**
* Remember the startup time, using no last-modified time before it.
*/
@Override
protected void initServletBean() {
this.pathMatcher = getPathMatcher();
this.startupTime = System.currentTimeMillis();
}
/**
* Return a PathMatcher to use for matching the "allowedResources" URL pattern.
* Default is AntPathMatcher.
* @see #setAllowedResources
* @see org.springframework.util.AntPathMatcher
*/
protected PathMatcher getPathMatcher() {
return new AntPathMatcher();
}
/**
* Determine the URL of the target resource and include it.
* @see #determineResourceUrl
*/
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 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 of this request.
* <p>Default implementation returns the value of the "resource" parameter.
* Can be overridden in subclasses.
* @param request current HTTP request
* @return the URL of the target resource, or <code>null</code> if none found
* @see #RESOURCE_PARAM_NAME
*/
protected String determineResourceUrl(HttpServletRequest request) {
return request.getParameter(RESOURCE_PARAM_NAME);
}
/**
* Include the specified default URL, if appropriate.
* @param request current HTTP request
* @param response current HTTP response
* @return whether a default URL was included
* @throws ServletException if thrown by the RequestDispatcher
* @throws IOException if thrown by the RequestDispatcher
*/
private boolean includeDefaultUrl(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
if (this.defaultUrl == null) {
return false;
}
doInclude(request, response, this.defaultUrl);
return true;
}
/**
* Include the specified resource via the RequestDispatcher.
* @param request current HTTP request
* @param response current HTTP response
* @param resourceUrl the URL of the target resource
* @throws ServletException if thrown by the RequestDispatcher
* @throws IOException if thrown by the RequestDispatcher
*/
private void doInclude(HttpServletRequest request, HttpServletResponse response, String resourceUrl)
throws ServletException, IOException {
if (this.contentType != null) {
response.setContentType(this.contentType);
}
String[] resourceUrls =
StringUtils.tokenizeToStringArray(resourceUrl, RESOURCE_URL_DELIMITERS);
for (int i = 0; i < resourceUrls.length; i++) {
// check whether URL matches allowed resources
if (this.allowedResources != null && !this.pathMatcher.match(this.allowedResources, resourceUrls[i])) {
throw new ServletException("Resource [" + resourceUrls[i] +
"] does not match allowed pattern [" + this.allowedResources + "]");
}
if (logger.isDebugEnabled()) {
logger.debug("Including resource [" + resourceUrls[i] + "]");
}
RequestDispatcher rd = request.getRequestDispatcher(resourceUrls[i]);
rd.include(request, response);
}
}
/**
* 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).
* <p>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.
* <p>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).
* @see #determineResourceUrl
* @see #getFileTimestamp
*/
@Override
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 file timestamp for the given resource.
* @param resourceUrl the URL of the resource
* @return the file timestamp in milliseconds, or -1 if not determinable
*/
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;
}
}
}
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