Valve (Tomcat API Documentation)
Keywords: org.apache.catalina.Valve interface

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## 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:
  $Revision: 1.1.1.1 $ $Date: 2002/07/18 16:47:38 $
Author:
  Craig R. McClanahan, Gunnar Rjnning, Peter Donald

Method Summary
`java.lang.String` | `getInfo()` Return descriptive information about this Valve implementation.
`void` | `invoke(Request request, Response response, ValveContext context)` Perform request processing as required by this Valve.

Method Detail

### getInfo

    public java.lang.String getInfo()

  Return descriptive information about this Valve implementation.

### invoke

    public void invoke(Request request,
                       Response response,
                       ValveContext context)
                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 `context.invokeNext()`.
  - 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 `invokeNext()` method has returned.
  - Perform any actions on the output stream associated with the specified Response after the `invokeNext()` method has returned.

  Parameters:
    `request` - The servlet request to be processed
    `response` - The servlet response to be created
    `context` - The valve context used to invoke the next valve in the current processing pipeline
  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

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