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org.apache.catalina
public interface: Valve [javadoc | source]

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.
Method from org.apache.catalina.Valve Summary:
backgroundProcess,   event,   getInfo,   getNext,   invoke,   setNext
Method from org.apache.catalina.Valve Detail:
 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.
 public  void event(Request request,
    Response response,
    CometEvent event) throws IOException, ServletException
    Process a Comet event.
 public String getInfo()
    Return descriptive information about this Valve implementation.
 public Valve getNext()
    Return the next Valve in the pipeline containing this Valve, if any.
 public  void invoke(Request request,
    Response response) throws IOException, 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.
 public  void setNext(Valve valve)
    Set the next Valve in the pipeline containing this Valve.