应用CumulativeProtocolDecoder
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package org.apache.mina.filter.codec;
import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.service.TransportMetadata;
import org.apache.mina.core.session.AttributeKey;
import org.apache.mina.core.session.IoSession;
/**
* A mailto:%7B@link ProtocolDecoder} that cumulates the content of received
* buffers to a <em>cumulative buffer</em> to help users implement decoders.
* <p>
* If the received mailto:%7B@link IoBuffer} is only a part of a message.
* decoders should cumulate received buffers to make a message complete or
* to postpone decoding until more buffers arrive.
* <p>
* Here is an example decoder that decodes CRLF terminated lines into
* <code>Command</code> objects:
* <pre>
* public class CrLfTerminatedCommandLineDecoder
* extends CumulativeProtocolDecoder {
*
* private Command parseCommand(IoBuffer in) {
* // Convert the bytes in the specified buffer to a
* // Command object.
* ...
* }
*
* protected boolean doDecode(
* IoSession session, IoBuffer in, ProtocolDecoderOutput out)
* throws Exception {
*
* // Remember the initial position.
* int start = in.position();
*
* // Now find the first CRLF in the buffer.
* byte previous = 0;
* while (in.hasRemaining()) {
* byte current = in.get();
*
* if (previous == '\r' && current == '\n') {
* // Remember the current position and limit.
* int position = in.position();
* int limit = in.limit();
* try {
* in.position(start);
* in.limit(position);
* // The bytes between in.position() and in.limit()
* // now contain a full CRLF terminated line.
* out.write(parseCommand(in.slice()));
* } finally {
* // Set the position to point right after the
* // detected line and set the limit to the old
* // one.
* in.position(position);
* in.limit(limit);
* }
* // Decoded one line; CumulativeProtocolDecoder will
* // call me again until I return false. So just
* // return true until there are no more lines in the
* // buffer.
* return true;
* }
*
* previous = current;
* }
*
* // Could not find CRLF in the buffer. Reset the initial
* // position to the one we recorded above.
* in.position(start);
*
* return false;
* }
* }
* </pre>
* <p>
* Please note that this decoder simply forward the call to
* mailto:%7B@link #doDecode(IoSession, IoBuffer, ProtocolDecoderOutput)} if the
* underlying transport doesn't have a packet fragmentation. Whether the
* transport has fragmentation or not is determined by querying
* mailto:%7B@link TransportMetadata}.
*
* @author The Apache MINA Project (dev@mina.apache.org)
* @version $Rev: 680990 $, $Date: 2008-07-30 19:58:19 +0800 (鏄熸湡涓� 30 涓冩湀 2008) $
*/
public abstract class CumulativeProtocolDecoder extends ProtocolDecoderAdapter {
private final AttributeKey BUFFER = new AttributeKey(getClass(), "buffer");
/**
* Creates a new instance.
*/
protected CumulativeProtocolDecoder() {
}
/**
* Cumulates content of <tt>in</tt> into internal buffer and forwards
* decoding request to mailto:%7B@link #doDecode(IoSession, IoBuffer, ProtocolDecoderOutput)}.
* <tt>doDecode()</tt> is invoked repeatedly until it returns <tt>false</tt>
* and the cumulative buffer is compacted after decoding ends.
*
* @throws IllegalStateException if your <tt>doDecode()</tt> returned
* <tt>true</tt> not consuming the cumulative buffer.
*/
public void decode(IoSession session, IoBuffer in,
ProtocolDecoderOutput out) throws Exception {
if (!session.getTransportMetadata().hasFragmentation()) {
doDecode(session, in, out);
return;
}
boolean usingSessionBuffer = true;
IoBuffer buf = (IoBuffer) session.getAttribute(BUFFER);
// If we have a session buffer, append data to that; otherwise
// use the buffer read from the network directly.
if (buf != null) {
boolean appended = false;
// Make sure that the buffer is auto-expanded.
if (buf.isAutoExpand()) {
try {
buf.put(in);
appended = true;
} catch (IllegalStateException e) {
// A user called derivation method (e.g. slice()),
// which disables auto-expansion of the parent buffer.
} catch (IndexOutOfBoundsException e) {
// A user disabled auto-expansion.
}
}
if (appended) {
buf.flip();
} else {
// Reallocate the buffer if append operation failed due to
// derivation or disabled auto-expansion.
buf.flip();
IoBuffer newBuf = IoBuffer.allocate(
buf.remaining() + in.remaining()).setAutoExpand(true);
newBuf.order(buf.order());
newBuf.put(buf);
newBuf.put(in);
newBuf.flip();
buf = newBuf;
// Update the session attribute.
session.setAttribute(BUFFER, buf);
}
} else {
buf = in;
usingSessionBuffer = false;
}
for (;;) {
int oldPos = buf.position();
boolean decoded = doDecode(session, buf, out);
if (decoded) {
if (buf.position() == oldPos) {
throw new IllegalStateException(
"doDecode() can't return true when buffer is not consumed.");
}
if (!buf.hasRemaining()) {
break;
}
} else {
break;
}
}
// if there is any data left that cannot be decoded, we store
// it in a buffer in the session and next time this decoder is
// invoked the session buffer gets appended to
if (buf.hasRemaining()) {
if (usingSessionBuffer && buf.isAutoExpand()) {
buf.compact();
} else {
storeRemainingInSession(buf, session);
}
} else {
if (usingSessionBuffer) {
removeSessionBuffer(session);
}
}
}
/**
* Implement this method to consume the specified cumulative buffer and
* decode its content into message(s).
*
* @param in the cumulative buffer
* @return <tt>true</tt> if and only if there's more to decode in the buffer
* and you want to have <tt>doDecode</tt> method invoked again.
* Return <tt>false</tt> if remaining data is not enough to decode,
* then this method will be invoked again when more data is cumulated.
* @throws Exception if cannot decode <tt>in</tt>.
*/
protected abstract boolean doDecode(IoSession session, IoBuffer in,
ProtocolDecoderOutput out) throws Exception;
/**
* Releases the cumulative buffer used by the specified <tt>session</tt>.
* Please don't forget to call <tt>super.dispose( session )</tt> when
* you override this method.
*/
@Override
public void dispose(IoSession session) throws Exception {
removeSessionBuffer(session);
}
private void removeSessionBuffer(IoSession session) {
session.removeAttribute(BUFFER);
}
private void storeRemainingInSession(IoBuffer buf, IoSession session) {
final IoBuffer remainingBuf = IoBuffer.allocate(buf.capacity()).setAutoExpand(true);
remainingBuf.order(buf.order());
remainingBuf.put(buf);
session.setAttribute(BUFFER, remainingBuf);
}
}
自定义协议解码器：
public class CommandDecoder extends CumulativeProtocolDecoder {
protected boolean doDecode(IoSession session, IoBuffer in,
ProtocolDecoderOutput out) throws Exception {
if (in.prefixedDataAvailable(4, Constants.MAX_COMMAND_LENGTH)) {
int length = in.getInt;
byte[] bytes = new byte[length];
in.get(bytes);
int commandNameLength = Constants.COMMAND_NAME_LENGTH;
byte[] cmdNameBytes = new byte[commandNameLength];
System.arraycopy(bytes, 0, cmdNameBytes, 0, commandNameLength);
String cmdName = StringUtils.trim(new String(cmdNameBytes));
AbstractTetrisCommand command = TetrisCommandFactory
.newCommand(cmdName);
if (command != null) {
byte[] cmdBodyBytes = new byte[length - commandNameLength];
System.arraycopy(bytes, commandNameLength, cmdBodyBytes, 0,
length - commandNameLength);
command.bodyFromBytes(cmdBodyBytes);
out.write(command);
}
return true;
} else {
return false;
}
}
这样就实现了粘包的存储，少包的等待，同时多包的处理