feature: WebSockets um ein exemplarisches JSON-Marshalling erweitert

Thomas Ziemer
1 parent 9144b122
Showing 3 changed files with 173 additions and 48 deletions
src/main/java/net/ziemers/swxercise/ui/ws/WebSocketController.java
src/main/java/net/ziemers/swxercise/ui/ws/WebSocketJson.java
src/main/webapp/websockets.html
@@ -4,7 +4,13 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
  
 import javax.annotation.PostConstruct;
-import javax.websocket.*;
+import javax.websocket.CloseReason;
+import javax.websocket.EncodeException;
+import javax.websocket.OnClose;
+import javax.websocket.OnError;
+import javax.websocket.OnMessage;
+import javax.websocket.OnOpen;
+import javax.websocket.Session;
 import javax.websocket.server.PathParam;
 import javax.websocket.server.ServerEndpoint;
 import java.io.IOException;
@@ -15,16 +21,18 @@ import java.util.Set;
 /**
  * Stub für die WebSocket-Unterstützung.
  *
- * Muss bei Bedarf noch um ein JSON-Marshalling erweitert werden.
- *
  * Aufgepasst: Mittels CDI kann nur @ApplicationScoped injiziert werden,
  * da während eines WebSocket-Callbacks kein Session-Kontext aktiv ist.
  */
-@ServerEndpoint(WebSocketController.serverEndpointPath)
+@ServerEndpoint(value = WebSocketController.serverEndpointPath,
+        encoders = { WebSocketJson.MessageEncoder.class },
+        decoders = { WebSocketJson.MessageDecoder.class } )
 public class WebSocketController {
  
     static final String serverEndpointPath = "/ws/api/v1/anEndpoint/{aParameter}";
  
+    // Eine Verknüpfung zwischen der WebSocket-Session und dem SessionContext des per REST
+    // angemeldeten Benutzers muss irgendwie auch noch realisiert werden. :)
     private static Set<Session> peers = Collections.synchronizedSet(new HashSet<>());
  
     private Logger logger;
@@ -48,15 +56,18 @@ public class WebSocketController {
     /**
      * Callback-Methode, die den Empfang einer neuen WebSocket-Nachricht signalisiert.
      *
-     * @param message der Inhalt der WebSocket-Nachricht
+     * @param json der JSON-strukturierte Inhalt der WebSocket-Nachricht
      * @param session das {@link Session}-Objekt der sendenden WebSocket-Verbindung
      */
     @OnMessage
-    public void onMessage(String message, Session session, @PathParam("aParameter") String param) {
-        logger.info("WebSocket Message '{}/{}' received by session id #{}", message, param, session.getId());
+    public void onMessage(WebSocketJson json,
+                          Session session,
+                          @PathParam("aParameter") String param) throws IOException, EncodeException {
+        logger.info("WebSocket Message '{}/{}' received by session id #{}",
+                json.getMessage(), param, session.getId());
         try {
-            // wir senden die empfangene Nachricht gleich wieder zurück
-            session.getBasicRemote().sendText(String.format("%s/%s", message, param));
+            // Wir senden die empfangene Nachricht gleich wieder zurück. Das Marshalling geschieht automatisch.
+            session.getBasicRemote().sendObject(json);
         } catch (IOException e) {
             e.printStackTrace();
         }
+package net.ziemers.swxercise.ui.ws;
+
+import javax.json.Json;
+import javax.json.JsonObject;
+import javax.json.JsonReader;
+import javax.json.JsonReaderFactory;
+import javax.websocket.DecodeException;
+import javax.websocket.Decoder;
+import javax.websocket.EncodeException;
+import javax.websocket.Encoder;
+import javax.websocket.EndpointConfig;
+import java.io.StringReader;
+import java.util.Collections;
+
+/**
+ * Ein Beispiel-JSON zur Übertragung durch den WebSocket.
+ */
+public class WebSocketJson {
+
+    /**
+     * Wandelt ein Objekt der Klasse in einen JSON-String um.
+     */
+    public static class MessageEncoder implements Encoder.Text<WebSocketJson> {
+
+        @Override
+        public void init(EndpointConfig config) {
+        }
+
+        @Override
+        public String encode(WebSocketJson message) throws EncodeException {
+            return Json.createObjectBuilder()
+                    .add("username", message.getUsername())
+                    .add("message", message.getMessage())
+                    .build()
+                    .toString();
+        }
+
+        @Override
+        public void destroy() {
+        }
+
+    }
+
+    /**
+     * Wandelt einen JSON-String in ein Objekt der Klasse um.
+     */
+    public static class MessageDecoder implements Decoder.Text<WebSocketJson> {
+
+        private JsonReaderFactory factory = Json.createReaderFactory(Collections.emptyMap());
+
+        @Override
+        public void init(EndpointConfig config) {
+        }
+
+        @Override
+        public WebSocketJson decode(String str) throws DecodeException {
+            WebSocketJson message = new WebSocketJson();
+            JsonReader reader = factory.createReader(new StringReader(str));
+            JsonObject json = reader.readObject();
+
+            message.setUsername(json.getString("username"));
+            message.setMessage(json.getString("message"));
+
+            return message;
+        }
+
+        @Override
+        public boolean willDecode(String str) {
+            return true;
+        }
+
+        @Override
+        public void destroy() {
+        }
+
+    }
+
+    /*
+     * Payload der JSON-Nachricht
+     */
+    private String username;
+
+    private String message;
+
+    private WebSocketJson() {}
+
+    public String getUsername() {
+        return username;
+    }
+
+    private void setUsername(String username) {
+        this.username = username;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    private void setMessage(String message) {
+        this.message = message;
+    }
+
+}
 <!DOCTYPE html>
-<html lang="en">
-<head>
-    <meta charset="UTF-8">
-    <title>Test WebSockets</title>
-</head>
-<body>
-    <script>
-        var url = "ws://localhost:8080/swxercise/ws/api/v1/anEndpoint/4711";
-        var webSocket = new WebSocket(url);
-
-        // Callback-Methoden für die WebSocket-Kommunikation
-        webSocket.onopen = function(e) { onWebSocketOpen(e) };
-        webSocket.onclose = function(e) { onWebSocketClose(e) };
-        webSocket.onmessage = function(e) { onWebSocketMessage(e) };
-        webSocket.onerror = function(e) { onWebSocketError(e) };
-
-        function onWebSocketOpen(e) {
-            console.log("WebSocket has been opened.");
-        }
-
-        function onWebSocketClose(e) {
-            console.log("WebSocket has been closed.");
-        }
-
-        function onWebSocketMessage(e) {
-            console.log("WebSocket Message '" + e.data + "' has been received.");
-        }
-
-        function onWebSocketError(e) {
-            alert("WebSocket Error " + e + " has been thrown!");
-        }
-
-        function sendWebSocketMessage() {
-            webSocket.send('Hello World!');
-            console.log("Tried to send WebSocket Message.");
-        }
-    </script>
-    <button onclick="sendWebSocketMessage()">Klick mich.</button>
-</body>
+<html lang="de">
+    <head>
+        <meta charset="UTF-8">
+        <title>Test WebSockets</title>
+    </head>
+
+    <body>
+        <script>
+            var url = "ws://localhost:8080/swxercise/ws/api/v1/anEndpoint/4711";
+            var webSocket = new WebSocket(url);
+
+            // Callback-Methoden für die WebSocket-Kommunikation
+            webSocket.onopen = function(e) { onWebSocketOpen(e) };
+            webSocket.onclose = function(e) { onWebSocketClose(e) };
+            webSocket.onmessage = function(e) { onWebSocketMessage(e) };
+            webSocket.onerror = function(e) { onWebSocketError(e) };
+
+            function onWebSocketOpen(e) {
+                console.log("WebSocket has been opened.");
+            }
+
+            function onWebSocketClose(e) {
+                console.log("WebSocket has been closed.");
+            }
+
+            function onWebSocketMessage(e) {
+                // JSON-String in ein JavaScript-Objekt konvertieren
+                var json = JSON.parse(e.data);
+
+                console.log("WebSocket Message '" + json.message + "' has been received.");
+            }
+
+            function onWebSocketError(e) {
+                alert("WebSocket Error " + e + " has been thrown!");
+            }
+
+            function sendWebSocketMessage() {
+                var json = {
+                    "username": "admin",
+                    "message": "Hello World!"
+                }
+
+                // JavaScript-Objekt in einen JSON-String konvertieren
+                webSocket.send(JSON.stringify(json));
+
+                console.log("Tried to send WebSocket Message.");
+            }
+        </script>
+        <button onclick="sendWebSocketMessage()">Klick mich.</button>
+    </body>
 </html>
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