apache mina 学习（十三）-----状态机和IoHander配合使用

现在我们把上一张的收录机的例子改造为一个tcp服务器,用文本的传输，效果如下;

telnet localhost 12345 S: + Greetings from your tape deck! C: list S: + (1: "The Knife - Silent Shout", 2: "Kings of convenience - Riot on an empty street") C: load 1 S: + "The Knife - Silent Shout" loaded C: play S: + Playing "The Knife - Silent Shout" C: pause S: + "The Knife - Silent Shout" paused C: play S: + Playing "The Knife - Silent Shout" C: info S: + Tape deck is playing. Current tape: "The Knife - Silent Shout" C: eject S: - Cannot eject while playing C: stop S: + "The Knife - Silent Shout" stopped C: eject S: + "The Knife - Silent Shout" ejected C: quit S: + Bye! Please come back! 完整的代码在org.apache.mina.example.tapedeck 包中
状态如下： @State public static final String ROOT = "Root"; @State(ROOT) public static final String EMPTY = "Empty"; @State(ROOT) public static final String LOADED = "Loaded"; @State(ROOT) public static final String PLAYING = "Playing"; @State(ROOT) public static final String PAUSED = "Paused";事件方法有些变化： @IoHandlerTransitions({ @IoHandlerTransition(on = MESSAGE_RECEIVED, in = LOADED, next = PLAYING), @IoHandlerTransition(on = MESSAGE_RECEIVED, in = PAUSED, next = PLAYING) }) public void playTape(TapeDeckContext context, IoSession session, PlayCommand cmd) { session.write("+ Playing \"" + context.tapeName + "\""); }我们没有使用上个例子中的Transaction注解，而是用了IoHandlerTransaction注解， 当为Mina的IoHandler创建一个状态机时，它会选择让你使用Java enum （枚举）类型来替代我们上面使用的字符串类型。这个在Mina的IoFilter中也是一样的。我们现在使用MESSAGE_RECEIVED来替代"play"来作为事件的名字(on是@IoHandlerTransition的一个属性)。这个常量是在org.apache.mina.statemachine.event.IoHandlerEvents中定义的，它的值是"messageReceived"，这个和Mina的IoHandler中的messageReceived()方法是一致的。同时我们自定义了一个StateContext状态上下文的实现 TapeDeckContext，主要作用就是用于返回当前收录机的名字。 static class TapeDeckContext extends AbstractStateContext { public String tapeName; } playTape()方法使用了PlayCommand命令来作为它的最后的一个参数 意味着只有在客户端发送的信息被编码成layCommand命令时，该方法才会被调用
@IoHandlerTransition(on = MESSAGE_RECEIVED, in = EMPTY, next = LOADED) public void loadTape(TapeDeckContext context, IoSession session, LoadCommand cmd) { if (cmd.getTapeNumber() < 1 || cmd.getTapeNumber() > tapes.length) { session.write("- Unknown tape number: " + cmd.getTapeNumber()); StateControl.breakAndGotoNext(EMPTY);//如果用户传递了非法的状态，则用empty代替 } else { context.tapeName = tapes[cmd.getTapeNumber() - 1]; session.write("+ \"" + context.tapeName + "\" loaded"); } } connect()方法将会在Mina开启一个会话并调用sessionOpened()方法时触发
@IoHandlerTransition(on = SESSION_OPENED, in = EMPTY) public void connect(IoSession session) { session.write("+ Greetings from your tape deck!"); } 它所做的工作就是向客户端发送欢迎的信息。状态机将会保持空的状态。pauseTape(), stopTape() 和 ejectTape() 方法和 playTape()很相似

错误处理如下：

@IoHandlerTransition(on = MESSAGE_RECEIVED, in = ROOT, weight = 10) public void error(Event event, StateContext context, IoSession session, Command cmd) { session.write("- Cannot " + cmd.getName() + " while " + context.getCurrentState().getId().toLowerCase()); }主方法： private static IoHandler createIoHandler() { StateMachine sm = StateMachineFactory.getInstance(IoHandlerTransition.class).create(EMPTY, new TapeDeckServer()); return new StateMachineProxyBuilder().setStateContextLookup( new IoSessionStateContextLookup(new StateContextFactory() { public StateContext create() { return new TapeDeckContext(); } })).create(IoHandler.class, sm); } // This code will work with MINA 1.0/1.1: public static void main(String[] args) throws Exception { SocketAcceptor acceptor = new SocketAcceptor(); SocketAcceptorConfig config = new SocketAcceptorConfig(); config.setReuseAddress(true); ProtocolCodecFilter pcf = new ProtocolCodecFilter( new TextLineEncoder(), new CommandDecoder()); config.getFilterChain().addLast("codec", pcf); acceptor.bind(new InetSocketAddress(12345), createIoHandler(), config); } // This code will work with MINA trunk: public static void main(String[] args) throws Exception { SocketAcceptor acceptor = new NioSocketAcceptor(); acceptor.setReuseAddress(true); ProtocolCodecFilter pcf = new ProtocolCodecFilter( new TextLineEncoder(), new CommandDecoder()); acceptor.getFilterChain().addLast("codec", pcf); acceptor.setHandler(createIoHandler()); acceptor.setLocalAddress(new InetSocketAddress(PORT)); acceptor.bind(); }

reateIoHandler() 方法创建了一个状态机，这个和我们之前所做的相似。除了我们一个IoHandlerTransition.class类来代替Transition.class 在StateMachineFactory.getInstance(...)方法中。这是我们在使用 @IoHandlerTransition 声明的时候必须要做的。当然这时我们使用了一个IoSessionStateContextLookup和一个自定义的StateContextFactory类，这个在我们创建一个IoHandler 代理时被使用到了。如果我们没有使用IoSessionStateContextLookup ，那么所有的客户端将会使用同一个状态机，这是我们不希望看到的。

main()方法创建了SocketAcceptor实例，并且绑定了一个ProtocolCodecFilter ，它用于编解码命令对象。最后它绑定了12345端口和IoHandler的实例。这个oHandler实例是由createIoHandler()方法创建的。