sessionCreate(IoSession)
IoSession对象被创建时的回调，一般用于进行会话初始化操作。注意：与sessionOpened(IoSession)不同，IoSession对象的创建并不意味着对应底层TCP连接的建立，而仅仅代表字面意思：一个IoSession对象被创建出来了。
sessionOpened(IoSession)
IoSession对象被打开时回调。在TCP中，该事件是在TCP连接建立时触发，一般可用于发起连接建立的握手、认证等操作。
sessionIdle(IoSession,IdleStatus)
IoSession对象超时时回调。当一个IoSession对象在指定的超时时常内没有读写事件发生，就会触发该事件，一般可用于通知服务器断开长时间闲置的连接等处理。具体的超时设置可由 IoService.setWriteIdleTime(int) ,IoService.setReadIdleTime(int) ,IoService.setBothIdleTime(int)设置。
messageReceived(IoSession,Object)
当接收到IoSession对Client发送的数据时回调。
messageSent(IoSession,Object)
当发送给IoSession对Client的数据发送成功时回调。
exceptionCaught(IoSession,Throwable)
当会话过程中出现异常时回调，通常用于错误处理。
session.write(Object)方法是一个异步方法，对该方法的调用并不会阻塞，而是向Mina投递一个异步的写操作，并返回一个可用于对已投递异步写操作进行控制的WriteFuture对象。例如：调用WriteFuture的await()或awaitUninterruptibly()，可由同步等待该异步操作的完成。
在I/O处理器中实现业务逻辑的时候，对于简单的情况，一般只需要在messageReceived中对传入的消息进行处理。如果需要写回数据到对等体，用IoSession.write()即可。
另外的情况，client和server的通信协议比较复杂，client是有状态变迁的，这时可用Mina提供的状态机实现，可使用IO处理器的实现更加简单。
androidpn中XmppIoHandler源代码：
package org.androidpn.server.xmpp.net;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.androidpn.server.xmpp.XmppServer;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.mina.core.service.IoHandler;
import org.apache.mina.core.session.IdleStatus;
import org.apache.mina.core.session.IoSession;
import org.dom4j.io.XMPPPacketReader;
import org.jivesoftware.openfire.net.MXParser;
import org.jivesoftware.openfire.nio.XMLLightweightParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;
/**
* This class is to create new sessions, destroy sessions and deliver
* received XML stanzas to the StanzaHandler.
*
* @author Sehwan Noh (devnoh@gmail.com)
*/
public class XmppIoHandler implements IoHandler {
private static final Log log = LogFactory.getLog(XmppIoHandler.class);
public static final String XML_PARSER = "XML_PARSER";
private static final String CONNECTION = "CONNECTION";
private static final String STANZA_HANDLER = "STANZA_HANDLER";
private String serverName;
private static Map<Integer, XMPPPacketReader> parsers = new ConcurrentHashMap<Integer, XMPPPacketReader>();
private static XmlPullParserFactory factory = null;
static {
try {
factory = XmlPullParserFactory.newInstance(
MXParser.class.getName(), null);
factory.setNamespaceAware(true);
} catch (XmlPullParserException e) {
log.error("Error creating a parser factory", e);
}
}
/**
* Constructor. Set the server name from server instance.
*/
protected XmppIoHandler() {
serverName = XmppServer.getInstance().getServerName();
}
/**
* Invoked from an I/O processor thread when a new connection has been created.
*/
public void sessionCreated(IoSession session) throws Exception {
log.debug("sessionCreated()...");
}
/**
* Invoked when a connection has been opened.
*/
public void sessionOpened(IoSession session) throws Exception {
log.debug("sessionOpened()...");
log.debug("remoteAddress=" + session.getRemoteAddress());
// Create a new XML parser
XMLLightweightParser parser = new XMLLightweightParser("UTF-8");
session.setAttribute(XML_PARSER, parser);
// Create a new connection
Connection connection = new Connection(session);
session.setAttribute(CONNECTION, connection);
session.setAttribute(STANZA_HANDLER, new StanzaHandler(serverName,
connection));
}
/**
* Invoked when a connection is closed.
*/
public void sessionClosed(IoSession session) throws Exception {
log.debug("sessionClosed()...");
Connection connection = (Connection) session.getAttribute(CONNECTION);
connection.close();
}
/**
* Invoked with the related IdleStatus when a connection becomes idle.
*/
public void sessionIdle(IoSession session, IdleStatus status)
throws Exception {
log.debug("sessionIdle()...");
Connection connection = (Connection) session.getAttribute(CONNECTION);
if (log.isDebugEnabled()) {
log.debug("Closing connection that has been idle: " + connection);
}
connection.close();
}
/**
* Invoked when any exception is thrown.
*/
public void exceptionCaught(IoSession session, Throwable cause)
throws Exception {
log.debug("exceptionCaught()...");
log.error(cause);
}
/**
* Invoked when a message is received.
*/
public void messageReceived(IoSession session, Object message)
throws Exception {
log.debug("messageReceived()...");
log.debug("RCVD: " + message);
// Get the stanza handler
StanzaHandler handler = (StanzaHandler) session
.getAttribute(STANZA_HANDLER);
// Get the XMPP packet parser
int hashCode = Thread.currentThread().hashCode();
XMPPPacketReader parser = parsers.get(hashCode);
if (parser == null) {
parser = new XMPPPacketReader();
parser.setXPPFactory(factory);
parsers.put(hashCode, parser);
}
// The stanza handler processes the message
try {
handler.process((String) message, parser);
} catch (Exception e) {
log.error(
"Closing connection due to error while processing message: "
+ message, e);
Connection connection = (Connection) session
.getAttribute(CONNECTION);
connection.close();
}
}
/**
* Invoked when a message written by IoSession.write(Object) is sent out.
*/
public void messageSent(IoSession session, Object message) throws Exception {
log.debug("messageSent()...");
}
} XmppIoHandler在加载的时候创建相关的xml解析工厂。
sessionOpened：在连接打开时候创建相关的xml的解析器和Handler处理器。
sessionClosed：关闭相关的连接。
sessionIdle：关闭相关的连接。
messageReceived：获取相关的xml解析器和handler处理器处理相关的消息。