org.apache.sling.api.servlets
Class SlingSafeMethodsServlet

java.lang.Object
  javax.servlet.GenericServlet
      org.apache.sling.api.servlets.SlingSafeMethodsServlet

All Implemented Interfaces:

Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

Direct Known Subclasses:

SlingAllMethodsServlet

public class SlingSafeMethodsServlet
extends javax.servlet.GenericServlet

Helper base class for read-only Servlets used in Sling. This base class is actually just a better implementation of the Servlet API HttpServlet class which accounts for extensibility. So extensions of this class have great control over what methods to overwrite.

If any of the default HTTP methods is to be implemented just overwrite the respective doXXX method. If additional methods should be supported implement appropriate doXXX methods and overwrite the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method to dispatch to the doXXX methods as appropriate and overwrite the getAllowedRequestMethods(Map) to add the new method names.

Please note, that this base class is intended for applications where data is only read. As such, this servlet by itself does not support the POST, PUT and DELETE methods. Extensions of this class should either overwrite any of the doXXX methods of this class or add support for other read-only methods only. Applications wishing to support data modification should rather use or extend the SlingAllMethodsServlet which also contains support for the POST, PUT and DELETE methods. This latter class should also be overwritten to add support for HTTP methods modifying data.

Implementors note: The methods in this class are all declared to throw the exceptions according to the intentions of the Servlet API rather than throwing their Sling RuntimeException counter parts. This is done to ease the integration with traditional servlets.

See Also:

SlingAllMethodsServlet, Serialized Form

Constructor Summary

SlingSafeMethodsServlet()

Method Summary

protected void	doGeneric(SlingHttpServletRequest request, SlingHttpServletResponse response) Called by the service(SlingHttpServletRequest, SlingHttpServletResponse) method to handle a request for an HTTP method, which is not known and handled by this class or its extension.
protected void	doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) Called by the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method to handle an HTTP GET request.
protected void	doHead(SlingHttpServletRequest request, SlingHttpServletResponse response) Handles the HEAD method.
protected void	doOptions(SlingHttpServletRequest request, SlingHttpServletResponse response) Handles the OPTIONS method by setting the HTTP Allow header on the response depending on the methods declared in this class.
protected void	doTrace(SlingHttpServletRequest request, SlingHttpServletResponse response) Handles the TRACE method by just returning the list of all header values in the response body.
protected StringBuffer	getAllowedRequestMethods(Map<String,Method> declaredMethods) Helper method called by doOptions(SlingHttpServletRequest, SlingHttpServletResponse) to calculate the value of the Allow header sent as the response to the HTTP OPTIONS request.
String	getServletInfo() Returns the simple class name of this servlet class.
protected void	handleMethodNotImplemented(SlingHttpServletRequest request, SlingHttpServletResponse response) Helper method which causes an appropriate HTTP response to be sent for an unhandled HTTP request method.
protected boolean	mayService(SlingHttpServletRequest request, SlingHttpServletResponse response) Tries to handle the request by calling a Java method implemented for the respective HTTP request method.
void	service(javax.servlet.ServletRequest req, javax.servlet.ServletResponse res) Forwards the request to the service(SlingHttpServletRequest, SlingHttpServletResponse) method if the request is a HTTP request.
protected void	service(SlingHttpServletRequest request, SlingHttpServletResponse response) Called by the service(ServletRequest, ServletResponse) method to handle the HTTP request.

Methods inherited from class javax.servlet.GenericServlet

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

Methods inherited from class java.lang.Object

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

Constructor Detail

SlingSafeMethodsServlet

public SlingSafeMethodsServlet()

Method Detail

doHead

protected void doHead(SlingHttpServletRequest request,
                      SlingHttpServletResponse response)
               throws javax.servlet.ServletException,
                      IOException

Handles the HEAD method.

This base implementation just calls the doGet(SlingHttpServletRequest, SlingHttpServletResponse) method dropping the output. Implementations of this class may overwrite this method if they have a more performing implementation. Otherwise, they may just keep this base implementation.

Parameters:

request - The HTTP request

response - The HTTP response which only gets the headers set

Throws:

javax.servlet.ServletException - Forwarded from the doGet(SlingHttpServletRequest, SlingHttpServletResponse) method called by this implementation.

IOException - Forwarded from the doGet(SlingHttpServletRequest, SlingHttpServletResponse) method called by this implementation.

doGet

protected void doGet(SlingHttpServletRequest request,
                     SlingHttpServletResponse response)
              throws javax.servlet.ServletException,
                     IOException

Called by the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method to handle an HTTP GET request.

This default implementation reports back to the client that the method is not supported.

Implementations of this class should overwrite this method with their implementation for the HTTP GET method support.

Parameters:

request - The HTTP request

response - The HTTP response

Throws:

javax.servlet.ServletException - Not thrown by this implementation.

IOException - If the error status cannot be reported back to the client.

doOptions

protected void doOptions(SlingHttpServletRequest request,
                         SlingHttpServletResponse response)
                  throws javax.servlet.ServletException,
                         IOException

Handles the OPTIONS method by setting the HTTP Allow header on the response depending on the methods declared in this class.

Extensions of this class should generally not overwrite this method but rather the getAllowedRequestMethods(Map) method. This method gathers all declared public and protected methods for the concrete class (upto but not including this class) and calls the getAllowedRequestMethods(Map) method with the methods gathered. The returned value is then used as the value of the Allow header set.

Parameters:

request - The HTTP request object. Not used.

response - The HTTP response object on which the header is set.

Throws:

javax.servlet.ServletException - Not thrown by this implementation.

IOException - Not thrown by this implementation.

doTrace

protected void doTrace(SlingHttpServletRequest request,
                       SlingHttpServletResponse response)
                throws javax.servlet.ServletException,
                       IOException

Handles the TRACE method by just returning the list of all header values in the response body.

Extensions of this class do not generally need to overwrite this method as it contains all there is to be done to the TRACE method.

Parameters:

request - The HTTP request whose headers are returned.

response - The HTTP response into which the request headers are written.

Throws:

javax.servlet.ServletException - Not thrown by this implementation.

IOException - May be thrown if there is an problem sending back the request headers in the response stream.

doGeneric

protected void doGeneric(SlingHttpServletRequest request,
                         SlingHttpServletResponse response)
                  throws javax.servlet.ServletException,
                         IOException

Called by the service(SlingHttpServletRequest, SlingHttpServletResponse) method to handle a request for an HTTP method, which is not known and handled by this class or its extension.

This default implementation reports back to the client that the method is not supported.

This method should be overwritten with great care. It is better to overwrite the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method and add support for any extension HTTP methods through an additional doXXX method.

Parameters:

request - The HTTP request

response - The HTTP response

Throws:

javax.servlet.ServletException - Not thrown by this implementation.

IOException - If the error status cannot be reported back to the client.

mayService

protected boolean mayService(SlingHttpServletRequest request,
                             SlingHttpServletResponse response)
                      throws javax.servlet.ServletException,
                             IOException

Tries to handle the request by calling a Java method implemented for the respective HTTP request method.

This base class implentation dispatches the HEAD, GET, OPTIONS and TRACE to the respective doXXX methods and returns true if any of these methods is requested. Otherwise false is just returned.

Implementations of this class may overwrite this method but should first call this base implementation and in case false is returned add handling for any other method and of course return whether the requested method was known or not.

Parameters:

request - The HTTP request

response - The HTTP response

Returns:

true if the requested method (request.getMethod()) is known. Otherwise false is returned.

Throws:

javax.servlet.ServletException - Forwarded from any of the dispatched methods

IOException - Forwarded from any of the dispatched methods

handleMethodNotImplemented

protected void handleMethodNotImplemented(SlingHttpServletRequest request,
                                          SlingHttpServletResponse response)
                                   throws IOException

Helper method which causes an appropriate HTTP response to be sent for an unhandled HTTP request method. In case of HTTP/1.1 a 405 status code (Method Not Allowed) is returned, otherwise a 400 status (Bad Request) is returned.

Parameters:

request - The HTTP request from which the method and protocol values are extracted to build the appropriate message.

response - The HTTP response to which the error status is sent.

Throws:

IOException - Thrown if the status cannot be sent to the client.

service

protected void service(SlingHttpServletRequest request,
                       SlingHttpServletResponse response)
                throws javax.servlet.ServletException,
                       IOException

Called by the service(ServletRequest, ServletResponse) method to handle the HTTP request. This implementation calls the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method and depedending on its return value call the doGeneric(SlingHttpServletRequest, SlingHttpServletResponse) method. If the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method can handle the request, the doGeneric(SlingHttpServletRequest, SlingHttpServletResponse) method is not called otherwise it is called.

Implementations of this class should not generally overwrite this method. Rather the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method should be overwritten to add support for more HTTP methods.

Parameters:

request - The HTTP request

response - The HTTP response

Throws:

javax.servlet.ServletException - Forwarded from the mayService(SlingHttpServletRequest, SlingHttpServletResponse) or doGeneric(SlingHttpServletRequest, SlingHttpServletResponse) methods.

IOException - Forwarded from the mayService(SlingHttpServletRequest, SlingHttpServletResponse) or doGeneric(SlingHttpServletRequest, SlingHttpServletResponse) methods.

service

public void service(javax.servlet.ServletRequest req,
                    javax.servlet.ServletResponse res)
             throws javax.servlet.ServletException,
                    IOException

Forwards the request to the service(SlingHttpServletRequest, SlingHttpServletResponse) method if the request is a HTTP request.

Implementations of this class will not generally overwrite this method.

Specified by:

service in interface javax.servlet.Servlet

Specified by:

service in class javax.servlet.GenericServlet

Parameters:

req - The Servlet request

res - The Servlet response

Throws:

javax.servlet.ServletException - If the request is not a HTTP request or forwarded from the service(SlingHttpServletRequest, SlingHttpServletResponse) called.

IOException - Forwarded from the service(SlingHttpServletRequest, SlingHttpServletResponse) called.

getServletInfo

public String getServletInfo()

Returns the simple class name of this servlet class. Extensions of this class may overwrite to return more specific information.

Specified by:

getServletInfo in interface javax.servlet.Servlet

Overrides:

getServletInfo in class javax.servlet.GenericServlet

getAllowedRequestMethods

protected StringBuffer getAllowedRequestMethods(Map<String,Method> declaredMethods)

Helper method called by doOptions(SlingHttpServletRequest, SlingHttpServletResponse) to calculate the value of the Allow header sent as the response to the HTTP OPTIONS request.

This base class implementation checks whether any doXXX methods exist for GET and HEAD and returns the list of methods supported found. The list returned always includes the HTTP OPTIONS and TRACE methods.

Implementations of this class may overwrite this method check for more methods supported by the extension (generally the same list as used in the mayService(SlingHttpServletRequest, SlingHttpServletResponse) method). This base class implementation should always be called to make sure the default HTTP methods are included in the list.

Parameters:

declaredMethods - The public and protected methods declared in the extension of this class.

Returns:

A StringBuffer containing the list of HTTP methods supported.