ChannelPipeline (Netty API Reference (3.9.9.Final))

All Known Implementing Classes:

DefaultChannelPipeline, StaticChannelPipeline
```
public interface ChannelPipeline
```
A list of ChannelHandlers which handles or intercepts ChannelEvents of a Channel. ChannelPipeline implements an advanced form of the Intercepting Filter pattern to give a user full control over how an event is handled and how the ChannelHandlers in the pipeline interact with each other.
Creation of a pipeline
For each new channel, a new pipeline must be created and attached to the channel. Once attached, the coupling between the channel and the pipeline is permanent; the channel cannot attach another pipeline to it nor detach the current pipeline from it.
The recommended way to create a new pipeline is to use the helper methods in Channels rather than calling an individual implementation's constructor:
```
 import static org.jboss.netty.channel.Channels.*;
 ChannelPipeline pipeline = pipeline(); // same with Channels.pipeline()
 
```
How an event flows in a pipeline
The following diagram describes how ChannelEvents are processed by ChannelHandlers in a ChannelPipeline typically. A ChannelEvent can be handled by either a ChannelUpstreamHandler or a ChannelDownstreamHandler and be forwarded to the closest handler by calling ChannelHandlerContext.sendUpstream(ChannelEvent) or ChannelHandlerContext.sendDownstream(ChannelEvent). The meaning of the event is interpreted somewhat differently depending on whether it is going upstream or going downstream. Please refer to ChannelEvent for more information.
```
                                       I/O Request
                                     via Channel or
                                 ChannelHandlerContext
                                           |
  +----------------------------------------+---------------+
  |                  ChannelPipeline       |               |
  |                                       \|/              |
  |  +----------------------+  +-----------+------------+  |
  |  | Upstream Handler  N  |  | Downstream Handler  1  |  |
  |  +----------+-----------+  +-----------+------------+  |
  |            /|\                         |               |
  |             |                         \|/              |
  |  +----------+-----------+  +-----------+------------+  |
  |  | Upstream Handler N-1 |  | Downstream Handler  2  |  |
  |  +----------+-----------+  +-----------+------------+  |
  |            /|\                         .               |
  |             .                          .               |
  |     [ sendUpstream() ]        [ sendDownstream() ]     |
  |     [ + INBOUND data ]        [ + OUTBOUND data  ]     |
  |             .                          .               |
  |             .                         \|/              |
  |  +----------+-----------+  +-----------+------------+  |
  |  | Upstream Handler  2  |  | Downstream Handler M-1 |  |
  |  +----------+-----------+  +-----------+------------+  |
  |            /|\                         |               |
  |             |                         \|/              |
  |  +----------+-----------+  +-----------+------------+  |
  |  | Upstream Handler  1  |  | Downstream Handler  M  |  |
  |  +----------+-----------+  +-----------+------------+  |
  |            /|\                         |               |
  +-------------+--------------------------+---------------+
                |                         \|/
  +-------------+--------------------------+---------------+
  |             |                          |               |
  |     [ Socket.read() ]          [ Socket.write() ]      |
  |                                                        |
  |  Netty Internal I/O Threads (Transport Implementation) |
  +--------------------------------------------------------+
 
```
An upstream event is handled by the upstream handlers in the bottom-up direction as shown on the left side of the diagram. An upstream handler usually handles the inbound data generated by the I/O thread on the bottom of the diagram. The inbound data is often read from a remote peer via the actual input operation such as InputStream.read(byte[]). If an upstream event goes beyond the top upstream handler, it is discarded silently.
A downstream event is handled by the downstream handler in the top-down direction as shown on the right side of the diagram. A downstream handler usually generates or transforms the outbound traffic such as write requests. If a downstream event goes beyond the bottom downstream handler, it is handled by an I/O thread associated with the Channel. The I/O thread often performs the actual output operation such as OutputStream.write(byte[]).
For example, let us assume that we created the following pipeline:
```
 ChannelPipeline p = Channels.pipeline();
 p.addLast("1", new UpstreamHandlerA());
 p.addLast("2", new UpstreamHandlerB());
 p.addLast("3", new DownstreamHandlerA());
 p.addLast("4", new DownstreamHandlerB());
 p.addLast("5", new UpstreamHandlerX());
 
```
In the example above, the class whose name starts with Upstream means it is an upstream handler. The class whose name starts with Downstream means it is a downstream handler.
In the given example configuration, the handler evaluation order is 1, 2, 3, 4, 5 when an event goes upstream. When an event goes downstream, the order is 5, 4, 3, 2, 1. On top of this principle, ChannelPipeline skips the evaluation of certain handlers to shorten the stack depth:
- 3 and 4 don't implement ChannelUpstreamHandler, and therefore the actual evaluation order of an upstream event will be: 1, 2, and 5.
- 1, 2, and 5 don't implement ChannelDownstreamHandler, and therefore the actual evaluation order of a downstream event will be: 4 and 3.
- If 5 extended SimpleChannelHandler which implements both ChannelUpstreamHandler and ChannelDownstreamHandler, the evaluation order of an upstream and a downstream event could be 125 and 543 respectively.
Building a pipeline

A user is supposed to have one or more ChannelHandlers in a pipeline to receive I/O events (e.g. read) and to request I/O operations (e.g. write and close). For example, a typical server will have the following handlers in each channel's pipeline, but your mileage may vary depending on the complexity and characteristics of the protocol and business logic:
1. Protocol Decoder - translates binary data (e.g. ChannelBuffer) into a Java object.
2. Protocol Encoder - translates a Java object into binary data.
3. ExecutionHandler - applies a thread model.
4. Business Logic Handler - performs the actual business logic (e.g. database access).
and it could be represented as shown in the following example:
```
 ChannelPipeline pipeline = Channels.pipeline();
 pipeline.addLast("decoder", new MyProtocolDecoder());
 pipeline.addLast("encoder", new MyProtocolEncoder());
 pipeline.addLast("executor", new ExecutionHandler(
         new OrderedMemoryAwareThreadPoolExecutor(16, 1048576, 1048576)));
 pipeline.addLast("handler", new MyBusinessLogicHandler());
 
```
Thread safety

A ChannelHandler can be added or removed at any time because a ChannelPipeline is thread safe. For example, you can insert a SslHandler when sensitive information is about to be exchanged, and remove it after the exchange.
Pitfall

Due to the internal implementation detail of the current default ChannelPipeline, the following code does not work as expected if FirstHandler is the last handler in the pipeline:
```
 public class FirstHandler extends SimpleChannelUpstreamHandler {

     @Override
     public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
         // Remove this handler from the pipeline,
         ctx.getPipeline().remove(this);
         // And let SecondHandler handle the current event.
         ctx.getPipeline().addLast("2nd", new SecondHandler());
         ctx.sendUpstream(e);
     }
 }
 
```
To implement the expected behavior, you have to add SecondHandler before the removal or make sure there is at least one more handler between FirstHandler and SecondHandler.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`addAfter(String baseName, String name, ChannelHandler handler)` Inserts a `ChannelHandler` after an existing handler of this pipeline.
`void`	`addBefore(String baseName, String name, ChannelHandler handler)` Inserts a `ChannelHandler` before an existing handler of this pipeline.
`void`	`addFirst(String name, ChannelHandler handler)` Inserts a `ChannelHandler` at the first position of this pipeline.
`void`	`addLast(String name, ChannelHandler handler)` Appends a `ChannelHandler` at the last position of this pipeline.
`void`	`attach(Channel channel, ChannelSink sink)` Attaches this pipeline to the specified `Channel` and `ChannelSink`.
`ChannelFuture`	`execute(Runnable task)` Schedules the specified task to be executed in the I/O thread associated with this pipeline's `Channel`.
`<T extends ChannelHandler> T`	`get(Class<T> handlerType)` Returns the `ChannelHandler` of the specified type in this pipeline.
`ChannelHandler`	`get(String name)` Returns the `ChannelHandler` with the specified name in this pipeline.
`Channel`	`getChannel()` Returns the `Channel` that this pipeline is attached to.
`ChannelHandlerContext`	`getContext(ChannelHandler handler)` Returns the context object of the specified `ChannelHandler` in this pipeline.
`ChannelHandlerContext`	`getContext(Class<? extends ChannelHandler> handlerType)` Returns the context object of the `ChannelHandler` of the specified type in this pipeline.
`ChannelHandlerContext`	`getContext(String name)` Returns the context object of the `ChannelHandler` with the specified name in this pipeline.
`ChannelHandler`	`getFirst()` Returns the first `ChannelHandler` in this pipeline.
`ChannelHandler`	`getLast()` Returns the last `ChannelHandler` in this pipeline.
`List<String>`	`getNames()` Returns the `List` of the handler names.
`ChannelSink`	`getSink()` Returns the `ChannelSink` that this pipeline is attached to.
`boolean`	`isAttached()` Returns `true` if and only if this pipeline is attached to a `Channel`.
`void`	`remove(ChannelHandler handler)` Removes the specified `ChannelHandler` from this pipeline.
`<T extends ChannelHandler> T`	`remove(Class<T> handlerType)` Removes the `ChannelHandler` of the specified type from this pipeline
`ChannelHandler`	`remove(String name)` Removes the `ChannelHandler` with the specified name from this pipeline.
`ChannelHandler`	`removeFirst()` Removes the first `ChannelHandler` in this pipeline.
`ChannelHandler`	`removeLast()` Removes the last `ChannelHandler` in this pipeline.
`void`	`replace(ChannelHandler oldHandler, String newName, ChannelHandler newHandler)` Replaces the specified `ChannelHandler` with a new handler in this pipeline.
`<T extends ChannelHandler> T`	`replace(Class<T> oldHandlerType, String newName, ChannelHandler newHandler)` Replaces the `ChannelHandler` of the specified type with a new handler in this pipeline.
`ChannelHandler`	`replace(String oldName, String newName, ChannelHandler newHandler)` Replaces the `ChannelHandler` of the specified name with a new handler in this pipeline.
`void`	`sendDownstream(ChannelEvent e)` Sends the specified `ChannelEvent` to the last `ChannelDownstreamHandler` in this pipeline.
`void`	`sendUpstream(ChannelEvent e)` Sends the specified `ChannelEvent` to the first `ChannelUpstreamHandler` in this pipeline.
`Map<String,ChannelHandler>`	`toMap()` Converts this pipeline into an ordered `Map` whose keys are handler names and whose values are handlers.

- Method Detail
  - addFirst
```
void addFirst(String name,
            ChannelHandler handler)
```
    Inserts a ChannelHandler at the first position of this pipeline.
    
    Parameters:
    name - the name of the handler to insert first
    handler - the handler to insert first
    
    Throws:
    
    IllegalArgumentException - if there's an entry with the same name already in the pipeline
    
    NullPointerException - if the specified name or handler is null
  - addLast
```
void addLast(String name,
           ChannelHandler handler)
```
    Appends a ChannelHandler at the last position of this pipeline.
    
    Parameters:
    name - the name of the handler to append
    handler - the handler to append
    
    Throws:
    
    IllegalArgumentException - if there's an entry with the same name already in the pipeline
    
    NullPointerException - if the specified name or handler is null
  - addBefore
```
void addBefore(String baseName,
             String name,
             ChannelHandler handler)
```
    Inserts a ChannelHandler before an existing handler of this pipeline.
    
    Parameters:
    baseName - the name of the existing handler
    name - the name of the handler to insert before
    handler - the handler to insert before
    
    Throws:
    
    NoSuchElementException - if there's no such entry with the specified baseName
    
    IllegalArgumentException - if there's an entry with the same name already in the pipeline
    
    NullPointerException - if the specified baseName, name, or handler is null
  - addAfter
```
void addAfter(String baseName,
            String name,
            ChannelHandler handler)
```
    Inserts a ChannelHandler after an existing handler of this pipeline.
    
    Parameters:
    baseName - the name of the existing handler
    name - the name of the handler to insert after
    handler - the handler to insert after
    
    Throws:
    
    NoSuchElementException - if there's no such entry with the specified baseName
    
    IllegalArgumentException - if there's an entry with the same name already in the pipeline
    
    NullPointerException - if the specified baseName, name, or handler is null
  - remove
```
void remove(ChannelHandler handler)
```
    Removes the specified ChannelHandler from this pipeline.
    
    Throws:
    
    NoSuchElementException - if there's no such handler in this pipeline
    
    NullPointerException - if the specified handler is null
  - remove
```
ChannelHandler remove(String name)
```
    Removes the ChannelHandler with the specified name from this pipeline.
    
    Returns:
    the removed handler
    
    Throws:
    
    NoSuchElementException - if there's no such handler with the specified name in this pipeline
    
    NullPointerException - if the specified name is null
  - remove
```
<T extends ChannelHandler> T remove(Class<T> handlerType)
```
    Removes the ChannelHandler of the specified type from this pipeline
    
    Type Parameters:
    T - the type of the handler
    Parameters:
    handlerType - the type of the handler
    
    Returns:
    the removed handler
    
    Throws:
    
    NoSuchElementException - if there's no such handler of the specified type in this pipeline
    
    NullPointerException - if the specified handler type is null
  - removeFirst
```
ChannelHandler removeFirst()
```
    Removes the first ChannelHandler in this pipeline.
    
    Returns:
    the removed handler
    
    Throws:
    
    NoSuchElementException - if this pipeline is empty
  - removeLast
```
ChannelHandler removeLast()
```
    Removes the last ChannelHandler in this pipeline.
    
    Returns:
    the removed handler
    
    Throws:
    
    NoSuchElementException - if this pipeline is empty
  - replace
```
void replace(ChannelHandler oldHandler,
           String newName,
           ChannelHandler newHandler)
```
    Replaces the specified ChannelHandler with a new handler in this pipeline.
    
    Throws:
    
    NoSuchElementException - if the specified old handler does not exist in this pipeline
    
    IllegalArgumentException - if a handler with the specified new name already exists in this pipeline, except for the handler to be replaced
    
    NullPointerException - if the specified old handler, new name, or new handler is null
  - replace
```
ChannelHandler replace(String oldName,
                     String newName,
                     ChannelHandler newHandler)
```
    Replaces the ChannelHandler of the specified name with a new handler in this pipeline.
    
    Returns:
    the removed handler
    
    Throws:
    
    NoSuchElementException - if the handler with the specified old name does not exist in this pipeline
    
    IllegalArgumentException - if a handler with the specified new name already exists in this pipeline, except for the handler to be replaced
    
    NullPointerException - if the specified old handler, new name, or new handler is null
  - replace
```
<T extends ChannelHandler> T replace(Class<T> oldHandlerType,
                                   String newName,
                                   ChannelHandler newHandler)
```
    Replaces the ChannelHandler of the specified type with a new handler in this pipeline.
    
    Returns:
    the removed handler
    
    Throws:
    
    NoSuchElementException - if the handler of the specified old handler type does not exist in this pipeline
    
    IllegalArgumentException - if a handler with the specified new name already exists in this pipeline, except for the handler to be replaced
    
    NullPointerException - if the specified old handler, new name, or new handler is null
  - getFirst
```
ChannelHandler getFirst()
```
    Returns the first ChannelHandler in this pipeline.
    
    Returns:
    the first handler. null if this pipeline is empty.
  - getLast
```
ChannelHandler getLast()
```
    Returns the last ChannelHandler in this pipeline.
    
    Returns:
    the last handler. null if this pipeline is empty.
  - get
```
ChannelHandler get(String name)
```
    Returns the ChannelHandler with the specified name in this pipeline.
    
    Returns:
    the handler with the specified name. null if there's no such handler in this pipeline.
  - get
```
<T extends ChannelHandler> T get(Class<T> handlerType)
```
    Returns the ChannelHandler of the specified type in this pipeline.
    
    Returns:
    the handler of the specified handler type. null if there's no such handler in this pipeline.
  - getContext
```
ChannelHandlerContext getContext(ChannelHandler handler)
```
    Returns the context object of the specified ChannelHandler in this pipeline.
    
    Returns:
    the context object of the specified handler. null if there's no such handler in this pipeline.
  - getContext
```
ChannelHandlerContext getContext(String name)
```
    Returns the context object of the ChannelHandler with the specified name in this pipeline.
    
    Returns:
    the context object of the handler with the specified name. null if there's no such handler in this pipeline.
  - getContext
```
ChannelHandlerContext getContext(Class<? extends ChannelHandler> handlerType)
```
    Returns the context object of the ChannelHandler of the specified type in this pipeline.
    
    Returns:
    the context object of the handler of the specified type. null if there's no such handler in this pipeline.
  - sendUpstream
```
void sendUpstream(ChannelEvent e)
```
    Sends the specified ChannelEvent to the first ChannelUpstreamHandler in this pipeline.
    
    Throws:
    
    NullPointerException - if the specified event is null
  - sendDownstream
```
void sendDownstream(ChannelEvent e)
```
    Sends the specified ChannelEvent to the last ChannelDownstreamHandler in this pipeline.
    
    Throws:
    
    NullPointerException - if the specified event is null
  - execute
```
ChannelFuture execute(Runnable task)
```
    Schedules the specified task to be executed in the I/O thread associated with this pipeline's Channel.
  - getChannel
```
Channel getChannel()
```
    Returns the Channel that this pipeline is attached to.
    
    Returns:
    the channel. null if this pipeline is not attached yet.
  - getSink
```
ChannelSink getSink()
```
    Returns the ChannelSink that this pipeline is attached to.
    
    Returns:
    the sink. null if this pipeline is not attached yet.
  - attach
```
void attach(Channel channel,
          ChannelSink sink)
```
    Attaches this pipeline to the specified Channel and ChannelSink. Once a pipeline is attached, it can't be detached nor attached again.
    
    Throws:
    
    IllegalStateException - if this pipeline is attached already
  - isAttached
```
boolean isAttached()
```
    Returns true if and only if this pipeline is attached to a Channel.
  - getNames
```
List<String> getNames()
```
    Returns the List of the handler names.
  - toMap
```
Map<String,ChannelHandler> toMap()
```
    Converts this pipeline into an ordered Map whose keys are handler names and whose values are handlers.

Interface ChannelPipeline

Creation of a pipeline

How an event flows in a pipeline

Building a pipeline

Thread safety

Pitfall

Method Summary

Method Detail

addFirst

addLast

addBefore

addAfter

remove

remove

remove

removeFirst

removeLast

replace

replace

replace

getFirst

getLast

get

get

getContext

getContext

getContext

sendUpstream

sendDownstream

execute

getChannel

getSink

attach

isAttached

getNames

toMap