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 ([email protected]) */ 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。