org.springframework.web.servlet
Class ResourceServlet

java.lang.Object
  javax.servlet.GenericServlet
      javax.servlet.http.HttpServlet
          org.springframework.web.servlet.HttpServletBean
              org.springframework.web.servlet.ResourceServlet

All Implemented Interfaces:

java.io.Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

public class ResourceServlet

extends HttpServletBean

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.

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).

Author:

Rod Johnson, Juergen Hoeller

See Also:

setDefaultUrl(java.lang.String), setAllowedResources(java.lang.String), setApplyLastModified(boolean), Serialized Form

Field Summary

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.

Fields inherited from class org.springframework.web.servlet.HttpServletBean

logger

Constructor Summary

ResourceServlet()

Method Summary

protected java.lang.String	determineResourceUrl(javax.servlet.http.HttpServletRequest request) Determine the URL of the target resource of this request.
protected void	doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) Determine the URL of the target resource and include it.
protected long	getFileTimestamp(java.lang.String resourceUrl) Return the file timestamp for the given resource.
protected long	getLastModified(javax.servlet.http.HttpServletRequest request) Return the last-modified timestamp of the file that corresponds to the target resource URL (i.e. typically the request ".jsp" file).
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.

Methods inherited from class org.springframework.web.servlet.HttpServletBean

addRequiredProperty, init, initBeanWrapper

Methods inherited from class javax.servlet.http.HttpServlet

doDelete, doHead, doOptions, doPost, doPut, doTrace, service, service

Methods inherited from class javax.servlet.GenericServlet

destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

RESOURCE_URL_DELIMITERS

public static final java.lang.String RESOURCE_URL_DELIMITERS

Any number of these characters are considered delimiters between multiple resource paths in a single String value.

See Also:

Constant Field Values

RESOURCE_PARAM_NAME

public static final java.lang.String RESOURCE_PARAM_NAME

Name of the parameter that must contain the actual resource path.

See Also:

Constant Field Values

Constructor Detail

ResourceServlet

public ResourceServlet()

Method Detail

setDefaultUrl

public 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.

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 Also:

setApplyLastModified(boolean)

setAllowedResources

public void setAllowedResources(java.lang.String allowedResources)

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

See Also:

PathMatcher.match(java.lang.String, java.lang.String)

setContentType

public void setContentType(java.lang.String 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.

setApplyLastModified

public void setApplyLastModified(boolean 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.

initServletBean

protected void initServletBean()

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

Overrides:

initServletBean in class HttpServletBean

doGet

protected final void doGet(javax.servlet.http.HttpServletRequest request,
                           javax.servlet.http.HttpServletResponse response)
                    throws javax.servlet.ServletException,
                           java.io.IOException

Determine the URL of the target resource and include it.

Throws:

javax.servlet.ServletException

java.io.IOException

See Also:

determineResourceUrl(javax.servlet.http.HttpServletRequest)

determineResourceUrl

protected java.lang.String determineResourceUrl(javax.servlet.http.HttpServletRequest request)

Determine the URL of the target resource of this request.

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

Parameters:

request - current HTTP request

Returns:

the URL of the target resource, or null if none found

See Also:

RESOURCE_PARAM_NAME

getLastModified

protected final long getLastModified(javax.servlet.http.HttpServletRequest request)

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).

See Also:

determineResourceUrl(javax.servlet.http.HttpServletRequest), getFileTimestamp(java.lang.String)

getFileTimestamp

protected long getFileTimestamp(java.lang.String resourceUrl)

Return the file timestamp for the given resource.

Parameters:

resourceUrl - the URL of the resource

Returns:

the file timestamp in milliseconds, or -1 if not determinable