public class ResourceServlet extends HttpServletBean
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).
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.
The defaultUrl
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.
The "resource" parameter and the defaultUrl
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.
The allowedResources
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!
If using this servlet for direct access rather than via includes,
the contentType
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.
To apply last-modified timestamps for the target resource, set the
applyLastModified
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.
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.
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.
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).
setDefaultUrl(java.lang.String)
,
setAllowedResources(java.lang.String)
,
setApplyLastModified(boolean)
Modifier and Type | Field and Description |
---|---|
private java.lang.String |
allowedResources |
private boolean |
applyLastModified |
private java.lang.String |
contentType |
private java.lang.String |
defaultUrl |
private PathMatcher |
pathMatcher |
static java.lang.String |
RESOURCE_PARAM_NAME
Name of the parameter that must contain the actual resource path.
|
static java.lang.String |
RESOURCE_URL_DELIMITERS
Any number of these characters are considered delimiters
between multiple resource paths in a single String value.
|
private long |
startupTime |
logger
Constructor and Description |
---|
ResourceServlet() |
Modifier and Type | Method and Description |
---|---|
protected java.lang.String |
determineResourceUrl(HttpServletRequest request)
Determine the URL of the target resource of this request.
|
protected void |
doGet(HttpServletRequest request,
HttpServletResponse response)
Determine the URL of the target resource and include it.
|
private void |
doInclude(HttpServletRequest request,
HttpServletResponse response,
java.lang.String resourceUrl)
Include the specified resource via the RequestDispatcher.
|
protected long |
getFileTimestamp(java.lang.String resourceUrl)
Return the file timestamp for the given resource.
|
protected long |
getLastModified(HttpServletRequest request)
Return the last-modified timestamp of the file that corresponds
to the target resource URL (i.e.
|
protected PathMatcher |
getPathMatcher()
Return a PathMatcher to use for matching the "allowedResources" URL pattern.
|
private boolean |
includeDefaultUrl(HttpServletRequest request,
HttpServletResponse response)
Include the specified default URL, if appropriate.
|
protected void |
initServletBean()
Remember the startup time, using no last-modified time before it.
|
void |
setAllowedResources(java.lang.String allowedResources)
Set allowed resources as URL pattern, e.g.
|
void |
setApplyLastModified(boolean applyLastModified)
Set whether to apply the file timestamp of the target resource
as last-modified value.
|
void |
setContentType(java.lang.String contentType)
Set the content type of the target resource (typically a JSP).
|
void |
setDefaultUrl(java.lang.String 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.
|
addRequiredProperty, createEnvironment, getEnvironment, getServletContext, getServletName, init, initBeanWrapper, setEnvironment
public static final java.lang.String RESOURCE_URL_DELIMITERS
public static final java.lang.String RESOURCE_PARAM_NAME
private java.lang.String defaultUrl
private java.lang.String allowedResources
private java.lang.String contentType
private boolean applyLastModified
private PathMatcher pathMatcher
private long startupTime
public void setDefaultUrl(java.lang.String defaultUrl)
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.
setApplyLastModified(boolean)
public void setAllowedResources(java.lang.String allowedResources)
AntPathMatcher
public void setContentType(java.lang.String contentType)
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 setApplyLastModified(boolean applyLastModified)
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.
protected void initServletBean()
initServletBean
in class HttpServletBean
protected PathMatcher getPathMatcher()
protected final void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, java.io.IOException
ServletException
java.io.IOException
determineResourceUrl(HttpServletRequest)
protected java.lang.String determineResourceUrl(HttpServletRequest request)
Default implementation returns the value of the "resource" parameter. Can be overridden in subclasses.
request
- current HTTP requestnull
if none foundRESOURCE_PARAM_NAME
private boolean includeDefaultUrl(HttpServletRequest request, HttpServletResponse response) throws ServletException, java.io.IOException
request
- current HTTP requestresponse
- current HTTP responseServletException
- if thrown by the RequestDispatcherjava.io.IOException
- if thrown by the RequestDispatcherprivate void doInclude(HttpServletRequest request, HttpServletResponse response, java.lang.String resourceUrl) throws ServletException, java.io.IOException
request
- current HTTP requestresponse
- current HTTP responseresourceUrl
- the URL of the target resourceServletException
- if thrown by the RequestDispatcherjava.io.IOException
- if thrown by the RequestDispatcherprotected final long getLastModified(HttpServletRequest request)
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 couldn't be resolved (for example, because the WAR is not expanded).
protected long getFileTimestamp(java.lang.String resourceUrl)
resourceUrl
- the URL of the resource