小例子说明
不是所有的Client都是前端页面，服务器也可能发起一个WebSocket连接，向其他服务器请求某项服务。小例子模拟两个WebSocket客户端，向server建立连接，当server收到消息时，向所有的连接的client分发该消息，当某个client连接或者关闭连接时，向其他client发布状态变化消息。
为了方便测试，client和server都在同一个web app中，要求client启动连接和发送消息，使用servlet进行触发。
二进制的消息
二进制消息需要进行序列化。在Java中对象序列化比JSON要高效，但是与非Java的程序互动，流行JSON。
public class ClusterMessage implements Serializable{ private static final long serialVersionUID = 1L; private String nodeId; private String message; public ClusterMessage(){ } public ClusterMessage(String nodeId , String message){ this.nodeId = nodeId; this.message = message; } public String getNodeId() { return nodeId; } public void setNodeId(String nodeId) { this.nodeId = nodeId; } public String getMessage() { return message; } public void setMessage(String message) { this.message = message; } }Cluster Server代码
我们重点学习如何解析二进制消息，如何发送二进制消息。
@ServerEndpoint("/clusterNodeSocket/{nodeId}")public class ClusterNodeServerEndpoint { //存储所有的client，以便进行消息广播 private static final List<Session> nodes = new ArrayList<>(2); @OnOpen public void onOpen(Session session, @PathParam("nodeId") String nodeId){ System.out.println("Node [" + nodeId + "] connected to cluster server"); ClusterMessage message = new ClusterMessage(nodeId, "Joined the cluster."); try { byte[] bytes = ClusterNodeServerEndpoint.toByteArray(message); for(Session node : nodes){ node.getBasicRemote().sendBinary(ByteBuffer.wrap(bytes)); } } catch (IOException e) { System.out.println("Exception when notifying of new node : " + e.toString()); e.printStackTrace(); } ClusterNodeServerEndpoint.nodes.add(session); } @OnMessage public void onMessage(Session session, byte[] message){ try{ for(Session node : ClusterNodeServerEndpoint.nodes){ if(node != session) node.getBasicRemote().sendBinary(ByteBuffer.wrap(message)); //发送二进制消息byte[] } }catch (IOException e) { logger.error("Exception when handling message on server : " + e.toString()); e.printStackTrace(); } } @OnClose public void onClose(Session session, @PathParam("nodeId") String nodeId){ System.out.println("Node [" + nodeId + "] disconnected."); ClusterNodeServerEndpoint.nodes.remove(session); ClusterMessage message = new ClusterMessage(nodeId, "Left the cluster."); try{ for(Session node : ClusterNodeServerEndpoint.nodes){ node.getBasicRemote().sendBinary(ByteBuffer.wrap( ClusterNodeServerEndpoint.toByteArray(message))); } }catch (IOException e) { System.out.println("Exception when notifying of left node : " + e.toString()); e.printStackTrace(); } } //将对象转换为byte[]： message(ClusterMessage) -> stream(ObjectOutputStream) --> output(ByteArrayOutputStream) private static byte[] toByteArray(ClusterMessage message) throws IOException { try(ByteArrayOutputStream output = new ByteArrayOutputStream(); ObjectOutputStream stream = new ObjectOutputStream(output)){ stream.writeObject(message); return output.toByteArray(); } }}Cluster Client代码
我们模拟两个webSocket clients，为了方便触发，采用Servlet。在web.xml中定义如下，将两个servlet指向同一个类
<servlet> <servlet-name>clusterNode1</servlet-name> <servlet-class>cn.wei.flowingflying.chapter10.cluster.ClusterNodeServlet</servlet-class> <init-param> <param-name>nodeId</param-name> <param-value>1</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>clusterNode2</servlet-name> <url-pattern>/clusterNode2</url-pattern> </servlet-mapping> <servlet> <servlet-name>clusterNode2</servlet-name> <servlet-class>cn.wei.flowingflying.chapter10.cluster.ClusterNodeServlet</servlet-class> <init-param> <param-name>nodeId</param-name> <param-value>2</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>clusterNode2</servlet-name> <url-pattern>/clusterNode2</url-pattern> </servlet-mapping>WebSocket代码如下：
//annotation @ClientEndpoint 不会像@ServiceEndpoint 那样自动实例化，只是作为一个有效endpoint的标记@ClientEndpointpublic class ClusterNodeServlet extends HttpServlet { private static final long serialVersionUID = 1L; private String nodeId; private Session session; //在init()时读取配置信息，建立webSocket连接 @Override public void init() throws ServletException { this.nodeId = this.getInitParameter("nodeId"); String path = this.getServletContext().getContextPath() + "/clusterNodeSocket/" + this.nodeId; try { //【1】连接webSocket server URI uri = new URI("ws","localhost:8080",path,null,null); this.session = ContainerProvider.getWebSocketContainer().connectToServer(this, uri); } catch (URISyntaxException | DeploymentException | IOException e) { e.printStackTrace(); throw new ServletException("Cannot connect to " + path + ".", e); } } @Override public void destroy() { try { this.session.close(); //关闭webSocket连接 } catch (IOException e) { e.printStackTrace(); } super.destroy(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //【2】发送对象的二进制消息 ClusterMessage message = new ClusterMessage(this.nodeId, "request:{ip:\"" + request.getRemoteAddr() + "\",queryString:\"" + request.getQueryString() + "\"}"); try(OutputStream output = this.session.getBasicRemote().getSendStream(); ObjectOutputStream stream = new ObjectOutputStream(output)){ stream.writeObject(message); } response.getWriter().append("OK"); } @OnMessage public void onMessage(InputStream input){ //【3】读二进制信息 try(ObjectInputStream stream = new ObjectInputStream(input)){ ClusterMessage message = (ClusterMessage)stream.readObject(); System.out.println("Node [" + this.nodeId + "]: Message received from cluster; node = " + message.getNodeId() + ", message = " + message.getMessage()); }catch (IOException | ClassNotFoundException e) { e.printStackTrace(); } } @OnClose public void onClose(CloseReason reason){ CloseReason.CloseCode code = reason.getCloseCode(); if(code != CloseReason.CloseCodes.NORMAL_CLOSURE){ System.out.println("WebSocket connection closed unexpectedly;" + " code = " + code + ", reason = " + reason.getReasonPhrase()); } }}相关链接： 我的Professional Java for Web Applications相关文章
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