Provides the JSP funtionality for OpenCms, with some additional utility functions.
How the JSP integration is done:
The issue for JSP integration was this:
In OpenCms all resources are residing in the OpenCms Database, the so called "Virtual File System" or VFS.
However, all JSP engines available read the JSP code from a file in the local file system.
The option to re-write a JSP engine so that it can read from the VFS would limit OpenCms
to running with this JSP engine only, which was not a choice.
So the approach that was taken is to dump the contents of the OpenCms JSP page from the VFS to the "real" file system
and then dispatch to the standard JSP engine.
Here is a top-level description of how this works:
- OpenCms gets the request through the {@link com.opencms.core.OpenCmsHttpServlet}
- The requested resource is identified as a JSP page (resource type {@link com.opencms.file.CmsResourceTypeJsp})
- The JSP launcher is started up with the laucher manager {@link com.opencms.launcher.CmsLauncherManager}
- The JSP launcher implements an additional interface: {@link com.opencms.flex.I_CmsResourceLoader}
- A resource loader is a new interface that was introduced with the FLEX release. The main
difference is that the original request / response is wrapped using a Servlet standard
{@link javax.servlet.http.HttpServletRequestWrapper} / {@link javax.servlet.http.HttpServletResponseWrapper}.
- On the first call to a page, the file contents of the JSP page are read from the OpenCms VFS
using the {@link com.opencms.file.CmsObject}
- The contents of the page are written to the "real" file system of the server,
in the default configuration to the directories
{WEBAPP-PATH}/opencms/WEB-INF/jsp/online
or
{WEBAPP-PATH}/opencms/WEB-INF/jsp/offline
(depending if the request was for the online or the offline
version of the page). The directory used can be configured in opencms.properties
.
- After the page is written to the "real" FS, the loader dispatches to the standard JSP mechanism with a simple
include()
call, this happens in {@link com.opencms.flex.CmsJspLoader#service(CmsObject cms, CmsResource file, CmsFlexRequest req, CmsFlexResponse res)}.
- The standard JSP mechanim will handle the JSP and deliver the output through the wrapped request / response
back to OpenCms.
- OpenCms will then deliver the contents back to the user.
Note: The FLEX package was originally developed to add only JSP functionality to OpenCms,
but has since then grown to include other methods and functionality.
@see com.opencms.core.OpenCmsHttpServlet
@see com.opencms.launcher.CmsLauncherManager
@see com.opencms.file.CmsObject
@see com.opencms.file.CmsResourceTypeJsp
@see com.opencms.flex.CmsJspLoader
@see com.opencms.flex.cache.CmsFlexRequestDispatcher
@see com.opencms.flex.cache.CmsFlexRequest
@see com.opencms.flex.cache.CmsFlexResponse
@since FLEX alpha 1