Package org.apache.catalina

## Interface Valve

- All Known Subinterfaces:
    `ClusterValve`
  All Known Implementing Classes:
    `AbstractAccessLogValve`, `AccessLogValve`, `AuthenticatorBase`, `BasicAuthenticator`, `ClusterSingleSignOn`, `CrawlerSessionManagerValve`, `DigestAuthenticator`, `ErrorReportValve`, `ExtendedAccessLogValve`, `FormAuthenticator`, `JDBCAccessLogValve`, `JsonErrorReportValve`, `JvmRouteBinderValve`, `LoadBalancerDrainingValve`, `NonLoginAuthenticator`, `PersistentValve`, `RemoteAddrValve`, `RemoteCIDRValve`, `RemoteHostValve`, `RemoteIpValve`, `ReplicationValve`, `RequestFilterValve`, `RewriteValve`, `SemaphoreValve`, `SingleSignOn`, `SpnegoAuthenticator`, `SSLAuthenticator`, `SSLValve`, `StuckThreadDetectionValve`, `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.
  Author:
    Craig R. McClanahan, Gunnar Rjnning, Peter Donald

- - ### Method Summary

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `void` | `backgroundProcess()` | Execute a periodic task, such as reloading, etc.
    `Valve` | `getNext()` |
    `void` | `invoke​(Request request, Response response)` | Perform request processing as required by this Valve.
    `boolean` | `isAsyncSupported()` |
    `void` | `setNext​(Valve valve)` | Set the next Valve in the pipeline containing this Valve.

- - ### Method Detail

    - #### getNext

          Valve getNext()

      Returns:
        the next Valve in the pipeline containing this Valve, if any.

    - #### setNext

          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

          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

          void invoke​(Request request,
                      Response response)
               throws java.io.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.
      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
        `ServletException` - if a servlet error occurs, or is thrown by a subsequently invoked Valve, Filter, or Servlet

    - #### isAsyncSupported

          boolean isAsyncSupported()