org.apache.catalina
Interface Valve

All Known Implementing Classes:

ValveBase

public interface Valve

A Valve is a request processing component associated with a particular Container. A series of Valves are generally associated with each other into a Pipeline. The detailed contract for a Valve is included in the description of the invoke() method below.

HISTORICAL NOTE: The "Valve" name was assigned to this concept because a valve is what you use in a real world pipeline to control and/or modify flows through it.

Version:

$Id: Valve.java 939531 2010-04-30 00:54:41Z kkolinko $

Author:

Craig R. McClanahan, Gunnar Rjnning, Peter Donald

Method Summary

void	backgroundProcess() Execute a periodic task, such as reloading, etc.
java.lang.String	getInfo() Return descriptive information about this Valve implementation.
Valve	getNext() Return the next Valve in the pipeline containing this Valve, if any.
void	invoke(Request request, Response response) Perform request processing as required by this Valve.
void	setNext(Valve valve) Set the next Valve in the pipeline containing this Valve.

Method Detail

getInfo

public java.lang.String getInfo()

Return descriptive information about this Valve implementation.

getNext

public Valve getNext()

Return the next Valve in the pipeline containing this Valve, if any.

setNext

public void setNext(Valve valve)

Set the next Valve in the pipeline containing this Valve.

Parameters:

valve - The new next valve, or null if none

backgroundProcess

public void backgroundProcess()

Execute a periodic task, such as reloading, etc. This method will be invoked inside the classloading context of this container. Unexpected throwables will be caught and logged.

invoke

public void invoke(Request request,
                   Response response)
            throws java.io.IOException,
                   javax.servlet.ServletException

Perform request processing as required by this Valve.

An individual Valve MAY perform the following actions, in the specified order:

• Examine and/or modify the properties of the specified Request and Response.
• Examine the properties of the specified Request, completely generate the corresponding Response, and return control to the caller.
• Examine the properties of the specified Request and Response, wrap either or both of these objects to supplement their functionality, and pass them on.
• If the corresponding Response was not generated (and control was not returned, call the next Valve in the pipeline (if there is one) by executing getNext().invoke().
• Examine, but not modify, the properties of the resulting Response (which was created by a subsequently invoked Valve or Container).

A Valve MUST NOT do any of the following things:

• Change request properties that have already been used to direct the flow of processing control for this request (for instance, trying to change the virtual host to which a Request should be sent from a pipeline attached to a Host or Context in the standard implementation).
• Create a completed Response AND pass this Request and Response on to the next Valve in the pipeline.
• Consume bytes from the input stream associated with the Request, unless it is completely generating the response, or wrapping the request before passing it on.
• Modify the HTTP headers included with the Response after the getNext().invoke() method has returned.
• Perform any actions on the output stream associated with the specified Response after the getNext().invoke() method has returned.

Parameters:

request - The servlet request to be processed

response - The servlet response to be created

Throws:

java.io.IOException - if an input/output error occurs, or is thrown by a subsequently invoked Valve, Filter, or Servlet

javax.servlet.ServletException - if a servlet error occurs, or is thrown by a subsequently invoked Valve, Filter, or Servlet