Support for Adding OnClosed Callbacks(#2821)

clients/java/signalr/src/main/java/com/microsoft/aspnet/signalr/Chat.java

@@ -20,6 +20,12 @@ public class Chat {
                 System.out.println("REGISTERED HANDLER: " + message);
             }, String.class);
 
+            hubConnection.onClosed((ex) -> {
+                if(ex.getMessage() != null){
+                    System.out.printf("There was an error: %s", ex.getMessage());
+                }
+            });
+
             //This is a blocking call
             hubConnection.start();
 

clients/java/signalr/src/main/java/com/microsoft/aspnet/signalr/HubConnection.java

@@ -8,6 +8,7 @@ import com.google.gson.JsonArray;
 import java.net.URISyntaxException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Consumer;
 
 public class HubConnection {
     private String url;
@@ -20,6 +21,7 @@ public class HubConnection {
     private static final String RECORD_SEPARATOR = "\u001e";
     private HubConnectionState connectionState = HubConnectionState.DISCONNECTED;
     private Logger logger;
+    private List<Consumer<Exception>> onClosedCallbackList;
 
     public HubConnection(String url, Transport transport, Logger logger){
         this.url = url;
@@ -162,6 +164,12 @@ public class HubConnection {
         transport.stop();
         connectionState = HubConnectionState.DISCONNECTED;
         logger.log(LogLevel.Information, "HubConnection stopped.");
+        if (onClosedCallbackList != null){
+            HubException hubException = new HubException(errorMessage);
+            for (Consumer<Exception> callback: onClosedCallbackList) {
+                callback.accept(hubException);
+            }
+        }
     }
 
     /**
@@ -406,4 +414,12 @@ public class HubConnection {
         handlers.remove(name);
         logger.log(LogLevel.Trace, "Removing handlers for client method %s" , name);
     }
+
+    public void onClosed(Consumer<Exception> callback) {
+        if (onClosedCallbackList == null){
+            onClosedCallbackList = new ArrayList<>();
+        }
+
+        onClosedCallbackList.add(callback);
+    }
 }

clients/java/signalr/src/main/java/com/microsoft/aspnet/signalr/HubException.java

@@ -0,0 +1,17 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+package com.microsoft.aspnet.signalr;
+
+public class HubException extends Exception {
+    public HubException() {
+    }
+
+    public HubException(String errorMessage) {
+        super(errorMessage);
+    }
+
+    public HubException(String errorMessage, Exception innerException) {
+        super(errorMessage, innerException);
+    }
+}

clients/java/signalr/src/test/java/HubConnectionTest.java

@@ -597,6 +597,65 @@ public class HubConnectionTest {
         assertEquals(1, value.get(), 0);
     }
 
+    @Test
+    public void onClosedCallbackRunsWhenStopIsCalled() throws Exception {
+        AtomicReference<String> value1 = new AtomicReference<>();
+        Transport mockTransport = new MockTransport();
+        HubConnection hubConnection = new HubConnection("http://example.com", mockTransport);
+        hubConnection.start();
+        hubConnection.onClosed((ex) -> {
+            assertNull(value1.get());
+            value1.set("Closed callback ran.");
+        });
+        hubConnection.stop();
+
+        assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
+        assertEquals(value1.get(), "Closed callback ran.");
+    }
+
+    @Test
+    public void multipleOnClosedCallbacksRunWhenStopIsCalled() throws Exception {
+        AtomicReference<String> value1 = new AtomicReference<>();
+        AtomicReference<String> value2 = new AtomicReference<>();
+        Transport mockTransport = new MockTransport();
+        HubConnection hubConnection = new HubConnection("http://example.com", mockTransport);
+        hubConnection.start();
+
+        hubConnection.onClosed((ex) -> {
+            assertNull(value1.get());
+            value1.set("Closed callback ran.");
+        });
+
+        hubConnection.onClosed((ex) -> {
+            assertNull(value2.get());
+            value2.set("The second onClosed callback ran");
+        });
+
+        assertNull(value1.get());
+        assertNull(value2.get());
+        hubConnection.stop();
+
+        assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
+        assertEquals("Closed callback ran.",value1.get());
+        assertEquals("The second onClosed callback ran", value2.get());
+    }
+
+    @Test
+    public void HubConnectionClosesAndRunsOnClosedCallbackAfterCloseMessageWithError() throws Exception {
+        MockTransport mockTransport = new MockTransport();
+        HubConnection hubConnection = new HubConnection("http://example.com", mockTransport);
+        hubConnection.onClosed((ex) -> {
+            assertEquals(ex.getMessage(), "There was an error");
+        });
+        hubConnection.start();
+        mockTransport.receiveMessage("{}" + RECORD_SEPARATOR);
+
+        assertEquals(HubConnectionState.CONNECTED, hubConnection.getConnectionState());
+
+        mockTransport.receiveMessage("{\"type\":7,\"error\": \"There was an error\"}" + RECORD_SEPARATOR);
+
+        assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
+    }
 
     private class MockTransport implements Transport {
         private OnReceiveCallBack onReceiveCallBack;

clients/java/signalr/src/test/java/HubExceptionTest.java

@@ -0,0 +1,24 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+import com.microsoft.aspnet.signalr.HubException;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class HubExceptionTest {
+    @Test
+    public void VeryHubExceptionMesssageIsSet() {
+        String errorMessage = "This is a HubException";
+        HubException hubException = new HubException(errorMessage);
+        assertEquals(hubException.getMessage(), errorMessage);
+    }
+
+    @Test
+    public void VeryHubExceptionInnerExceptionIsSet() {
+        String errorMessage = "This is the inner exception of the HubException";
+        Exception innerException = new Exception(errorMessage);
+        HubException hubException = new HubException(null, innerException);
+        assertEquals(hubException.getCause().getMessage(), errorMessage);
+    }
+}