SlingServletDelegate (Apache Sling 8 API)

java.lang.Object
- javax.servlet.GenericServlet
- - org.apache.sling.launchpad.base.webapp.SlingServletDelegate

All Implemented Interfaces:

Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig, Launcher
```
public class SlingServletDelegate
extends javax.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 javax.servlet.Servlet.
- Handles requests by delegating to a servlet which is expected to be registered with the framework as a service of type javax.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:

Serialized Form

Constructor Summary

Constructors
Constructor and Description

SlingServletDelegate()

Constructors
Constructor and Description
`SlingServletDelegate()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`destroy()` Destroys this servlet by shutting down the OSGi framework and hence the delegatee servlet if one is set at all.
`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.
`void`	`service(javax.servlet.ServletRequest req, javax.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 javax.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 Detail
  - SlingServletDelegate
```
public SlingServletDelegate()
```
- Method Detail
  - 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
  - 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
  - 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
  - start
```
public boolean start()
```
    Description copied from interface: Launcher
    
    Starts the framework and returns true if successfull.
    
    Specified by:
    
    start in interface Launcher
  - 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 javax.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 javax.servlet.GenericServlet
    
    Throws:
    
    javax.servlet.ServletException - if the framework cannot be initialized.
  - service
```
public final void service(javax.servlet.ServletRequest req,
                          javax.servlet.ServletResponse res)
                   throws javax.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 javax.servlet.Servlet
    
    Specified by:
    
    service in class javax.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:
    
    javax.servlet.UnavailableException - if the no delegatee servlet is currently available
    
    javax.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 javax.servlet.Servlet
    
    Overrides:
    
    destroy in class javax.servlet.GenericServlet

Class SlingServletDelegate

Constructor Summary

Method Summary

Methods inherited from class javax.servlet.GenericServlet

Methods inherited from class java.lang.Object

Constructor Detail

SlingServletDelegate

Method Detail

setNotifiable

setCommandLine

setSlingHome

start

stop

init

service

destroy