Package org.jboss.netty.buffer

Abstraction of a byte buffer - the fundamental data structure to represent a low-level binary and text message.

See: Description

Interface Summary

Interface	Description
ChannelBuffer	A random and sequential accessible sequence of zero or more bytes (octets).
ChannelBufferFactory	A factory that creates or pools ChannelBuffers.
ChannelBufferIndexFinder	Locates an index of data in a ChannelBuffer.
WrappedChannelBuffer	The common interface for buffer wrappers and derived buffers.

Class Summary

Class	Description
AbstractChannelBuffer	A skeletal implementation of a buffer.
AbstractChannelBufferFactory	A skeletal implementation of ChannelBufferFactory.
BigEndianHeapChannelBuffer	A big-endian Java heap buffer.
ByteBufferBackedChannelBuffer	A NIO ByteBuffer based buffer.
ChannelBufferInputStream	An InputStream which reads data from a ChannelBuffer.
ChannelBufferOutputStream	An OutputStream which writes data to a ChannelBuffer.
ChannelBuffers	Creates a new ChannelBuffer by allocating new space or by wrapping or copying existing byte arrays, byte buffers and a string.
CompositeChannelBuffer	A virtual buffer which shows multiple buffers as a single merged buffer.
DirectChannelBufferFactory	A ChannelBufferFactory which pre-allocates a large chunk of direct buffer and returns its slice on demand.
DuplicatedChannelBuffer	A derived buffer which simply forwards all data access requests to its parent.
DynamicChannelBuffer	A dynamic capacity buffer which increases its capacity as needed.
HeapChannelBuffer	A skeletal implementation for Java heap buffers.
HeapChannelBufferFactory	A ChannelBufferFactory which merely allocates a heap buffer with the specified capacity.
LittleEndianHeapChannelBuffer	A little-endian Java heap buffer.
ReadOnlyChannelBuffer	A derived buffer which forbids any write requests to its parent.
SlicedChannelBuffer	A derived buffer which exposes its parent's sub-region only.
TruncatedChannelBuffer	A derived buffer which hides its parent's tail data beyond a certain index.

Package org.jboss.netty.buffer Description

Abstraction of a byte buffer - the fundamental data structure to represent a low-level binary and text message. Netty uses its own buffer API instead of NIO ByteBuffer to represent a sequence of bytes. This approach has significant advantage over using ByteBuffer. Netty's new buffer type, ChannelBuffer, has been designed from ground up to address the problems of ByteBuffer and to meet the daily needs of network application developers. To list a few cool features:

• You can define your buffer type if necessary.
• Transparent zero copy is achieved by built-in composite buffer type.
• A dynamic buffer type is provided out-of-the-box, whose capacity is expanded on demand, just like StringBuffer.
• There's no need to call the flip() method anymore.
• It is often faster than ByteBuffer.

Extensibility

ChannelBuffer has rich set of operations optimized for rapid protocol implementation. For example, ChannelBuffer provides various operations for accessing unsigned values and strings and searching for certain byte sequence in a buffer. You can also extend or wrap existing buffer type to add convenient accessors. The custom buffer type still implements ChannelBuffer interface rather than introducing an incompatible type.

Transparent Zero Copy

To lift up the performance of a network application to the extreme, you need to reduce the number of memory copy operation. You might have a set of buffers that could be sliced and combined to compose a whole message. Netty provides a composite buffer which allows you to create a new buffer from the arbitrary number of existing buffers with no memory copy. For example, a message could be composed of two parts; header and body. In a modularized application, the two parts could be produced by different modules and assembled later when the message is sent out.

 +--------+----------+
 | header |   body   |
 +--------+----------+
 

If ByteBuffer were used, you would have to create a new big buffer and copy the two parts into the new buffer. Alternatively, you can perform a gathering write operation in NIO, but it restricts you to represent the composite of buffers as an array of ByteBuffers rather than a single buffer, breaking the abstraction and introducing complicated state management. Moreover, it's of no use if you are not going to read or write from an NIO channel.

 // The composite type is incompatible with the component type.
 ByteBuffer[] message = new ByteBuffer[] { header, body };
 

By contrast, ChannelBuffer does not have such caveats because it is fully extensible and has a built-in composite buffer type.

 // The composite type is compatible with the component type.
 ChannelBuffer message = ChannelBuffers.wrappedBuffer(header, body);

 // Therefore, you can even create a composite by mixing a composite and an
 // ordinary buffer.
 ChannelBuffer messageWithFooter = ChannelBuffers.wrappedBuffer(message, footer);

 // Because the composite is still a ChannelBuffer, you can access its content
 // easily, and the accessor method will behave just like it's a single buffer
 // even if the region you want to access spans over multiple components.  The
 // unsigned integer being read here is located across body and footer.
 messageWithFooter.getUnsignedInt(
     messageWithFooter.readableBytes() - footer.readableBytes() - 1);
 

Automatic Capacity Extension

Many protocols define variable length messages, which means there's no way to determine the length of a message until you construct the message or it is difficult and inconvenient to calculate the length precisely. It is just like when you build a String. You often estimate the length of the resulting string and let StringBuffer expand itself on demand. Netty allows you to do the same via a dynamic buffer which is created by the ChannelBuffers.dynamicBuffer() method.

 // A new dynamic buffer is created.  Internally, the actual buffer is created
 // lazily to avoid potentially wasted memory space.
 ChannelBuffer b = ChannelBuffers.dynamicBuffer(4);

 // When the first write attempt is made, the internal buffer is created with
 // the specified initial capacity (4).
 b.writeByte('1');

 b.writeByte('2');
 b.writeByte('3');
 b.writeByte('4');

 // When the number of written bytes exceeds the initial capacity (4), the
 // internal buffer is reallocated automatically with a larger capacity.
 b.writeByte('5');
 

Better Performance

Most frequently used buffer implementation of ChannelBuffer is a very thin wrapper of a byte array (i.e. byte[]). Unlike ByteBuffer, it has no complicated boundary check and index compensation, and therefore it is easier for a JVM to optimize the buffer access. More complicated buffer implementation is used only for sliced or composite buffers, and it performs as well as ByteBuffer.