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

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## org.apache.catalina
Interface Pipeline

All Known Implementing Classes:
  ContainerBase, StandardPipeline

public interface Pipeline

Interface describing a collection of Valves that should be executed in sequence when the `invoke()` method is invoked. It is required that a Valve somewhere in the pipeline (usually the last one) must process the request and create the corresponding response, rather than trying to pass the request on.

There is generally a single Pipeline instance associated with each Container. The container's normal request processing functionality is generally encapsulated in a container-specific Valve, which should always be executed at the end of a pipeline. To facilitate this, the `setBasic()` method is provided to set the Valve instance that will always be executed last. Other Valves will be executed in the order that they were added, before the basic Valve is executed.

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

Method Summary
`void` | `addValve(Valve valve)` Add a new Valve to the end of the pipeline associated with this Container.
`Valve` | `getBasic()` Return the Valve instance that has been distinguished as the basic Valve for this Pipeline (if any).
`Valve[]` | `getValves()` Return the set of Valves in the pipeline associated with this Container, including the basic Valve (if any).
`void` | `invoke(Request request, Response response)` Cause the specified request and response to be processed by the Valves associated with this pipeline, until one of these valves causes the response to be created and returned.
`void` | `removeValve(Valve valve)` Remove the specified Valve from the pipeline associated with this Container, if it is found; otherwise, do nothing.
`void` | `setBasic(Valve valve)` Set the Valve instance that has been distinguished as the basic Valve for this Pipeline (if any).

Method Detail

### getBasic

    public Valve getBasic()

  Return the Valve instance that has been distinguished as the basic Valve for this Pipeline (if any).

### setBasic

    public void setBasic(Valve valve)

  Set the Valve instance that has been distinguished as the basic Valve for this Pipeline (if any). Prioer to setting the basic Valve, the Valve's `setContainer()` will be called, if it implements `Contained`, with the owning Container as an argument. The method may throw an `IllegalArgumentException` if this Valve chooses not to be associated with this Container, or `IllegalStateException` if it is already associated with a different Container.

  Parameters:
    `valve` - Valve to be distinguished as the basic Valve

### addValve

    public void addValve(Valve valve)

  Add a new Valve to the end of the pipeline associated with this Container. Prior to adding the Valve, the Valve's `setContainer()` method will be called, if it implements `Contained`, with the owning Container as an argument. The method may throw an `IllegalArgumentException` if this Valve chooses not to be associated with this Container, or `IllegalStateException` if it is already associated with a different Container.

  Parameters:
    `valve` - Valve to be added
  Throws:
    `java.lang.IllegalArgumentException` - if this Container refused to accept the specified Valve
    `java.lang.IllegalArgumentException` - if the specifie Valve refuses to be associated with this Container
    `java.lang.IllegalStateException` - if the specified Valve is already associated with a different Container

### getValves

    public Valve[] getValves()

  Return the set of Valves in the pipeline associated with this Container, including the basic Valve (if any). If there are no such Valves, a zero-length array is returned.

### invoke

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

  Cause the specified request and response to be processed by the Valves associated with this pipeline, until one of these valves causes the response to be created and returned. The implementation must ensure that multiple simultaneous requests (on different threads) can be processed through the same Pipeline without interfering with each other's control flow.

  Parameters:
    `request` - The servlet request we are processing
    `response` - The servlet response we are creating
  Throws:
    `java.io.IOException` - if an input/output error occurs
    `javax.servlet.ServletException` - if a servlet exception is thrown

### removeValve

    public void removeValve(Valve valve)

  Remove the specified Valve from the pipeline associated with this Container, if it is found; otherwise, do nothing. If the Valve is found and removed, the Valve's `setContainer(null)` method will be called if it implements `Contained`.

  Parameters:
    `valve` - Valve to be removed

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