Package org.apache.sling.launchpad.base.webapp

Class SlingServletDelegate

java.lang.Object
jakarta.servlet.GenericServlet
org.apache.sling.launchpad.base.webapp.SlingServletDelegate
All Implemented Interfaces:
jakarta.servlet.Servlet, jakarta.servlet.ServletConfig, Serializable, Launcher
public class SlingServletDelegate extends jakarta.servlet.GenericServlet implements Launcher
The SlingServletDelegate serves as a basic servlet for Project Sling. The tasks of this servlet are as follows:
  • The init() method launches Apache Felix as the OSGi framework implementation we use.
  • Registers as a service listener interested for services of type jakarta.servlet.Servlet.
  • Handles requests by delegating to a servlet which is expected to be registered with the framework as a service of type jakarta.servlet.Servlet. If no delegatee servlet has been registered request handlings results in a temporary unavailability of the servlet.

Request Handling

This servlet handles request by forwarding to a delegatee servlet. The delegatee servlet is automatically retrieved from the service registry by the getDelegatee(). This method also makes sure, the such a servlet actually exits by throwing an UnvailableException if not and also makes sure the servlet is initialized.

Launch Configuration

The Apache Felix framework requires configuration parameters to be specified for startup. This servlet builds the list of parameters from three locations:

  1. The sling.properties is read from the servlet class path. This properties file contains default settings.
  2. Extensions of this servlet may provide additional properties to be loaded overwriting the loadConfigProperties(String) method.
  3. Finally, web application init parameters are added to the properties and may overwrite existing properties of the same name(s).

After loading all properties, variable substitution takes place on the property values. A variable is indicated as ${<prop-name>} where <prop-name> is the name of a system or configuration property (configuration properties override system properties). Variables may be nested and are resolved from inner-most to outer-most. For example, the property value ${outer-${inner}} is resolved by first resolving ${inner} and then resolving the property whose name is the catenation of outer- and the result of resolving ${inner}.

Logging

This servlet logs through the servlet container logging mechanism by calling the GenericServlet.log methods. Bundles launched within the framework provided by this servlet may use whatever logging mechanism they choose to use. The Commons OSGI Log Bundle provides an OSGi Log Service implementation, which also provides access to Apache Commons Logging, SLF4J and Log4J logging. It is recommended that this bundle is used to setup and configure logging for systems based on this servlet.

See Also:

  • Constructor Summary

    Constructors
    Constructor
    Description
    SlingServletDelegate()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    protected String
    calculateServletPackages(String servletVersion, int majorVersion)
     
    final void
    destroy()
    Destroys this servlet by shutting down the OSGi framework and hence the delegatee servlet if one is set at all.
    final void
    init()
    Initializes this servlet by loading the framework configuration properties, starting the OSGi framework (Apache Felix) and exposing the system bundle context and the Felix instance as servlet context attributes.
    final void
    service(jakarta.servlet.ServletRequest req, jakarta.servlet.ServletResponse res)
    Services the request by delegating to the delegatee servlet.
    void
    setCommandLine(Map<String,String> args)
    The commandline provided from the standalone launch case.
    void
    setNotifiable(Notifiable notifiable)
    The Notifiable to notify on framework stop or update
    void
    setSlingHome(String slingHome)
    Sets the sling.home to be used for starting the framework.
    boolean
    start()
    Starts the framework and returns true if successfull.
    void
    stop()
    Stops the framework.

    Methods inherited from class jakarta.servlet.GenericServlet

    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

  • Constructor Details

    • SlingServletDelegate

      public SlingServletDelegate()

  • Method Details

    • setNotifiable

      public void setNotifiable(Notifiable notifiable)
      Description copied from interface: Launcher
      The Notifiable to notify on framework stop or update
      Specified by:
      setNotifiable in interface Launcher
      Parameters:
      notifiable - The notifiable

    • setCommandLine

      public void setCommandLine(Map<String,String> args)
      Description copied from interface: Launcher
      The commandline provided from the standalone launch case.
      Specified by:
      setCommandLine in interface Launcher
      Parameters:
      args - The commandline

    • setSlingHome

      public void setSlingHome(String slingHome)
      Description copied from interface: Launcher
      Sets the sling.home to be used for starting the framework. This method must be called with a non-null argument before trying to start the framework.
      Specified by:
      setSlingHome in interface Launcher
      Parameters:
      slingHome - The sling.home directory

    • start

      public boolean start()
      Description copied from interface: Launcher
      Starts the framework and returns true if successfull.
      Specified by:
      start in interface Launcher
      Returns:
      true if the framework has been started successfully

    • stop

      public void stop()
      Description copied from interface: Launcher
      Stops the framework. This method only returns when the framework has actually been stopped. This method may be used by the main class or servlet to initiate a shutdown of the framework.
      Specified by:
      stop in interface Launcher

    • init

      public final void init() throws jakarta.servlet.ServletException
      Initializes this servlet by loading the framework configuration properties, starting the OSGi framework (Apache Felix) and exposing the system bundle context and the Felix instance as servlet context attributes.
      Overrides:
      init in class jakarta.servlet.GenericServlet
      Throws:
      jakarta.servlet.ServletException - if the framework cannot be initialized.

    • service

      public final void service(jakarta.servlet.ServletRequest req, jakarta.servlet.ServletResponse res) throws jakarta.servlet.ServletException, IOException
      Services the request by delegating to the delegatee servlet. If no delegatee servlet is available, a UnavailableException is thrown.
      Specified by:
      service in interface jakarta.servlet.Servlet
      Specified by:
      service in class jakarta.servlet.GenericServlet
      Parameters:
      req - the ServletRequest object that contains the client's request
      res - the ServletResponse object that will contain the servlet's response
      Throws:
      jakarta.servlet.UnavailableException - if the no delegatee servlet is currently available
      jakarta.servlet.ServletException - if an exception occurs that interferes with the servlet's normal operation occurred
      IOException - if an input or output exception occurs

    • destroy

      public final void destroy()
      Destroys this servlet by shutting down the OSGi framework and hence the delegatee servlet if one is set at all.
      Specified by:
      destroy in interface jakarta.servlet.Servlet
      Overrides:
      destroy in class jakarta.servlet.GenericServlet

    • calculateServletPackages

      protected String calculateServletPackages(String servletVersion, int majorVersion)