Java for Web学习笔记（四六）：WebSocket（3）Java Server

Maven相关库

<dependency>    <groupId>javax.websocket</groupId>    <artifactId>javax.websocket-api</artifactId>    <version>1.1</version>    <scope>provided</scope></dependency>

注意，这里是provided，不是compiled，已经集成在JavaEE 7中。上面是支持WebSocket Server和Client的，如果我们只需要Client，可以使用：

<dependency>    <groupId>javax.websocket</groupId>    <artifactId>javax.websocket-client-api</artifactId>    <version>1.1</version>    <scope>provided</scope></dependency>

一个简单的WebSocket Server

承接之前WebSocket Client的小例子，server在收到WebSocket请求后发出Hello消息，然后采用异步方式，每隔1秒发送一个消息，连发三次，然后关闭连接。

//【1】进行websocket server endpoint的标注，给出匹配的url。当收到一个webSocket请求时，会创建一个实例，这点和Servlet不一样，需要注意。@ServerEndpoint("/test/{id}")public class TestServer {    //【2】server和client握手后，同样提供了@OnOpen, @OnClose, @OnError和@OnMessage触发发放，这些方法可以通过@PathParam()来获取path的信息，如本例中的id。我们可以通过javax.websocket.Session来发送信息和关闭连接    //【2.1】可选的Session参数，可选的EndpointConfig参数，以及path信息    @OnOpen    public void onOpen(Session session, @PathParam("id") String id){        System.out.println("onOpen : (" + id + ")");        try {            session.getBasicRemote().sendText("Hello, " + id);            new Thread(new Runnable() {                public void run() {                    for(int i = 0 ; i < 3 ; i ++){                        try {                            Thread.sleep(1000);                            session.getBasicRemote().sendText("count " + i);                        } catch (Exception e) {                        }                                            }                   try {                       session.close();                   } catch (IOException ignoreE) {                   }               }            }).start();        } catch (IOException e) {            e.printStackTrace();        }            }    //【2.2】消息的参数会比较复杂    //    1、String给出text消息，如本例    //    2、String以及boolean表示chunks，true表示为最后一个chunks。    //    3、One Java primitive or primitive wrapper to receive an entire text message converted to that type    //    4、One java.io.Reader to receive a text message as a blocking stream    //    5、One byte[] or one java.nio.ByteBuffer to receive an entire binary message    //    6、One byte[] or one ByteBuffer, plus one boolean to receive a binary message in chunks    //    7、One java.io.InputStream to receive a binary message as a blocking stream    //    8、One PongMessage for custom handling of heartbeat responses    //    9、Any Java object if the endpoint has a Decoder.Text, Decoder.Binary, Decoder .TextStream, or Decoder.BinaryStream registered to convert that type. The message type of text or binary must match the registered decoder.    @OnMessage    public void onMessage(Session session, String message, @PathParam("id") String id){        System.out.println("onMessage : (" + id + ") " + message);    }    //【2.3】可选的Session参数，可选的CloseReason参数，以及path信息    @OnClose    public void onClose(Session session, @PathParam("id") String id){        System.out.println("onClose : (" + id + ")");    }    //【2.4】@OnError提供可选的Session参数，必选的Throwable，以及path信息，本例无处理}

更为复杂一点的处理

两个client之间的通信

server可以作为agent之类的，实现两个或者多个client之间的通信，方式很简单，将session关联即可。

@ServerEndpoint("/ticTacToe/{gameId}/{username}")public class GameServer {    private static class Game{        public long gameId;        public Session player1;        public Session player2;        public TicTacToeGame ticTacToeGame;        }    //我们通过gameId可以获得两个关联的client的session。    private static Map<Long, Game> games = new Hashtable<>();    ... 略 ...}

使用JSON作为Message

Gson是一个选择，我们也可以使用可能更为传统的方式：

    <dependency>        <groupId>com.fasterxml.jackson.core</groupId>        <artifactId>jackson-core</artifactId>        <version>2.8.7</version>        <scope>compile</scope>    </dependency>    <dependency>        <groupId>com.fasterxml.jackson.core</groupId>        <artifactId>jackson-annotations</artifactId>        <version>2.8.7</version>        <scope>compile</scope>    </dependency>    <dependency>        <groupId>com.fasterxml.jackson.core</groupId>        <artifactId>jackson-databind</artifactId>        <version>2.8.7</version>        <scope>compile</scope>    </dependency>    <dependency>        <groupId>com.fasterxml.jackson.datatype</groupId>        <artifactId>jackson-datatype-jsr310</artifactId>        <version>2.8.7</version>        <scope>compile</scope>    </dependency>

@ServerEndpoint("/ticTacToe/{gameId}/{username}")public class GameServer {    ... 见上面代码片段，略 ...    //（1）消息的基础格式    public static abstract class Message{        private final String action;        public Message(String action){            this.action = action;        }        public String getAction() {            return action;        }            }    //（2）具体的消息类型    public static class GameStartedMessage extends Message{        private final TicTacToeGame game;        public GameStartedMessage(TicTacToeGame game) {            super("gameStarted");            this.game = game;        }        public TicTacToeGame getGame() {            return game;        }            }    ... 其他的消息类型，略 ...    //【1】定义json封装    private static ObjectMapper mapper = new ObjectMapper();    //【2】发送JSON消息    private void sendJsonMessage(Session session, Game game, Message message){        try {            session.getBasicRemote().sendText(GameServer.mapper.writeValueAsString(message));        } catch (Exception e) {            handleException(e,game);        }     }    //【3】解析JSON消息    @OnMessage    public void onMessage(Session session, String message, @PathParam("gameId") long gameId){        Game game = GameServer.games.get(gameId);        ... ...        //解析JSON        MoveMessage move = GameServer.mapper.readValue(message, MoveMessage.class);        ... ...        //发送JSON        this.sendJsonMessage((isPlayer1 ? game.player2 : game.player1), game,                    new OpponentMadeMoveMessage(move));    }}

从session中获取信息

在jsp文件中，我们用javascript写到

server = new WebSocket('ws://' + window.location.host +                            '<c:url value="/game/${gameId}/${username}">'                            +'<c:param name="action" value="${action}" />'                            +'</c:url>');

我们要读出握手的HTTP请求的相关信息，例如action参数的值

//在WebSocket server中，如果我们需要获取action的信息//getRequestParameterMap：Return the request parameters associated with the request this session was opened under.List<String> actions = session.getRequestParameterMap().get("action");if(actions != null && actions.size() == 1){    String action = actions.get(0);    ... ...}

相关链接： 我的Professional Java for Web Applications相关文章