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 java.nio.ByteBuffer to represent a sequence of bytes. This approach has significant advantage over using java.nio.ByteBuffer. Netty's new buffer type, io.netty.buffer.ByteBuf, has been designed from ground up to address the problems of java.nio.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 java.lang.StringBuffer.
• There's no need to call the flip() method anymore.
• It is often faster than java.nio.ByteBuffer.

Extensibility

io.netty.buffer.ByteBuf has rich set of operations optimized for rapid protocol implementation. For example, io.netty.buffer.ByteBuf 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 io.netty.buffer.ByteBuf 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 java.nio.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 java.nio.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, io.netty.buffer.ByteBuf 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.
io.netty.buffer.ByteBuf message = io.netty.buffer.Unpooled.wrappedBuffer(header, body);

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

// Because the composite is still a io.netty.buffer.ByteBuf, 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 java.lang.String. You often estimate the length of the resulting string and let java.lang.StringBuffer expand itself on demand.

// A new dynamic buffer is created.  Internally, the actual buffer is created
// lazily to avoid potentially wasted memory space.
io.netty.buffer.ByteBuf b = io.netty.buffer.Unpooled.buffer(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 io.netty.buffer.ByteBuf is a very thin wrapper of a byte array (i.e. byte[]). Unlike java.nio.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 java.nio.ByteBuffer.