org.jboss.netty.handler.codec.frame

Class LengthFieldPrepender

java.lang.Object

org.jboss.netty.handler.codec.oneone.OneToOneEncoder

org.jboss.netty.handler.codec.frame.LengthFieldPrepender

All Implemented Interfaces:

ChannelDownstreamHandler, ChannelHandler

@ChannelHandler.Sharable
public class LengthFieldPrepender
extends OneToOneEncoder

An encoder that prepends the length of the message. The length value is prepended as a binary form. It is encoded in either big endian or little endian depending on the default ByteOrder of the current ChannelBufferFactory.

For example, LengthFieldPrepender(2) will encode the following 12-bytes string:

 +----------------+
 | "HELLO, WORLD" |
 +----------------+
 

into the following:

 +--------+----------------+
 + 0x000C | "HELLO, WORLD" |
 +--------+----------------+
 

If you turned on the lengthIncludesLengthFieldLength flag in the constructor, the encoded data would look like the following (12 (original data) + 2 (prepended data) = 14 (0xE)):

 +--------+----------------+
 + 0x000E | "HELLO, WORLD" |
 +--------+----------------+
 

Nested Class Summary

Nested classes/interfaces inherited from interface org.jboss.netty.channel.ChannelHandler

ChannelHandler.Sharable

Field Summary

Fields

Modifier and Type	Field and Description
private int	lengthFieldLength
private boolean	lengthIncludesLengthFieldLength

Constructor Summary

Constructors

Constructor and Description
LengthFieldPrepender(int lengthFieldLength) Creates a new instance.
LengthFieldPrepender(int lengthFieldLength, boolean lengthIncludesLengthFieldLength) Creates a new instance.

Method Summary

Modifier and Type	Method and Description
protected java.lang.Object	encode(ChannelHandlerContext ctx, Channel channel, java.lang.Object msg) Transforms the specified message into another message and return the transformed message.

Methods inherited from class org.jboss.netty.handler.codec.oneone.OneToOneEncoder

doEncode, handleDownstream

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

lengthFieldLength

private final int lengthFieldLength

lengthIncludesLengthFieldLength

private final boolean lengthIncludesLengthFieldLength

Constructor Detail

LengthFieldPrepender

public LengthFieldPrepender(int lengthFieldLength)

Creates a new instance.

Parameters:

lengthFieldLength - the length of the prepended length field. Only 1, 2, 3, 4, and 8 are allowed.

Throws:

java.lang.IllegalArgumentException - if lengthFieldLength is not 1, 2, 3, 4, or 8

LengthFieldPrepender

public LengthFieldPrepender(int lengthFieldLength,
                            boolean lengthIncludesLengthFieldLength)

Creates a new instance.

Parameters:

lengthFieldLength - the length of the prepended length field. Only 1, 2, 3, 4, and 8 are allowed.

lengthIncludesLengthFieldLength - if true, the length of the prepended length field is added to the value of the prepended length field.

Throws:

java.lang.IllegalArgumentException - if lengthFieldLength is not 1, 2, 3, 4, or 8

Method Detail

encode

protected java.lang.Object encode(ChannelHandlerContext ctx,
                                  Channel channel,
                                  java.lang.Object msg)
                           throws java.lang.Exception

Description copied from class: OneToOneEncoder

Transforms the specified message into another message and return the transformed message. Note that you can not return null, unlike you can in OneToOneDecoder.decode(ChannelHandlerContext, Channel, Object); you must return something, at least ChannelBuffers.EMPTY_BUFFER.

Specified by:

encode in class OneToOneEncoder

Throws:

java.lang.Exception