Providing Web Console Plugins
The Web Console can be extended by registering an OSGi service for the interface javax.servlet.Servlet
with the service property felix.webconsole.label
set to the label (last segment in the URL) of the page. The respective service is called a Web Console Plugin or a plugin for short.
The most basic plugin is a plain old Servlet whose service(ServletRequest, ServletResponse)
method is called by the Apache Felix Web Console. Before calling the servlet the web console sets two request attributes helping the plugin rendering the response:
felix.webconsole.appRoot
-- This request attribute of typeString
provides the absolute path of the Web Console root. This path consists of the servlet context path (fromServletRequest.getContextPath()
) and the Web Console servlet path (fromHttpServletRequest.getServletPath()
,/system/console
by default). This attribute can be used to provide absolute links to resources (images, CSS, scripts, etc.) or other plugins. This request attribute is available to client side JavaScript as the globalappRoot
variable.felix.webconsole.pluginRoot
-- This request attribute of typeString
provides the absolute path of the current plugin. This path consists of the servlet context path (fromServletRequest.getContextPath()
), the Web Console servlet path (fromHttpServletRequest.getServletPath()
,/system/console
by default) and the plugin label. This attribute can be used to provide absolute links to the plugin itself. This request attribute is available to client side JavaScript as the globalpluginRoot
variable.felix.webconsole.labelMap
-- This request attribute of typeMap
provides a mapping of labels to page titles of registered console plugins. This map may be used to render a navigation of the console plugins such as theAbstractWebConsolePlugin.renderTopNavigation
method does. The keys and values of the map are of typeString
.
To help rendering the response the Apache Felix Web Console bundle provides two options: One option is to extend the AbstractWebConsolePlugin
overwriting the renderContent
method. The other option is to register the servlet with another service registration property to indicate the desire to wrap the response.
Extending The AbstractWebConsolePlugin¶
To leverage the rendering of the common header and footer around the plugin's data area, the plugin can extend the abstract org.apache.felix.webconsole.AbstractWebConsolePlugin
class implementing the following methods:
renderContext(HttpServletRequest, HttpServletResponse)
-- This method is called to render the actual plugin data area.getLabel()
-- Returns the last path segment of the plugin page. This should return the value to which thefelix.webconsole.label
service registration propery is set.getTitle()
-- Returns a human readable title to be displayed at the top of the plugin page.getCssReferences()
-- See the section Providing CSS Files below.
To fully leverage the AbstractWebConsolePlugin
it must be initialiazed before registering the extension as a service. Likewise after unregistering the service, the plugin should be destroyed. To this avail the following methods are provided in the AbstractWebConsolePlugin
:
activateBundle(BundleContext)
-- Initializes the plugin with theBundleContext
and prepares some data to be rendered in the header and footer areas.deactivate()
-- Destroys the plugin.
In addition to these OSGi-oriented setup methods the Web Console itself will call the Servlet.init(ServletConfig)
method before putting the plugin into service and the Servlet.destroy()
method when the plugin is removed.
Providing CSS Files¶
Part of rendering the header, the AbstractWebConsolePlugin
also emits links to CSS files to include for displaying the page. Since such CSS links may only be present in the header section of the generated HTML the getCssReferences()
method is provided. This method is called to create links for additional CSS files. The default implementation of this method returns null
meaning no additional CSS links to be rendered. Extensions of the AbstractWebConsolePlugin
may overwrite this method to provide a list of CSS links.
The CSS links provided by the getCssReferences()
method may be absolute or relative paths, though relative paths are recommended. Relative paths are turned into absolute path by prepending them with the value of the felix.webconsole.appRoot
request attribute.
Transparent Response Wrapping¶
While being very simple and straight forward, extending the AbstractWebConsolePlugin
actually creates a binding from the plugin provider bundle to the Web Console bundle, which may be undesired. To support the use case of wanting the benefits of the AbstractWebConsolePlugin
but wiring independency of the Web Console, a plugin servlet may be registered with a second service registration property (besides the required felix.webconsole.label
):
felix.webconsole.title
-- If registered servlet does not extend theAbstractWebConsolePlugin
but provides this property (of typeString
) the servlet is wrapped in an adapter to theAbstractWebConsolePlugin
which callsServlet.service(ServletRequest, ServletResponse)
method on behalf of therenderContent
implementation.felix.webconsole.css
-- Defines a single string, an array of strings or a Collection of strings to be used as the values provided by thegetCssReferences()
method. This property is optional. If this property is missing or if the value does not have the correct type, thegetCssReferences()
just returnsnull
assuming there are no additional CSS resources to reference.
The wrapper around the plugin itself extends the AbstractWebConsolePlugin
as follows:
renderContext(HttpServletRequest, HttpServletResponse)
-- Calls theservice(HttpServletRequest, HttpServletResponse)
method of the plugin to render the actual contents of the plugin.getLabel()
-- Returns the value of thefelix.webconsole.label
service registration property of the plugin.getTitle()
-- Returns the value of thefelix.webconsole.title
service registration property of the plugin.getCssReferences()
-- Returns the values of thefelix.webconsole.css
service registration property of the plugin.service(ServletRequest, ServletResponse)
-- If the request method isGET
theservice(ServletRequest, ServletResponse)
method of theAbstractWebConsolePlugin
is called which ultimately calls theservice
method. For all other requests, theservice(ServletRequest, ServletResponse)
method of the plugin is called directly to have the plugin handle any non-GET
requests directly.
Please note, that sometimes it is not desirable to have the AbstractWebConsolePlugin
render the header and footer of the response. For this reason, the AbstractWebConsolePlugin
only renders the header and footer if the request to such a wrapped plugin either has no extension or if the extension is .html
. For any other extension, e.g. .txt
or .json
, the header and footer is not rendered and the service
method of the plugin is directly called.
It is suggested that plugins extend from the javax.servlet.http.HttpServlet
class and implement the appropriate doXxx(HttpServletRequest, HttpServletResponse)
methods such as doGet
and doPost
. In addition, unless non-GET requests are handled through AJAX calls, it is suggested that non-GET requests return a redirect after processing the request.