Check HubConnection state before running invoke logic (#4400)

eng/PatchConfig.props

@@ -31,6 +31,7 @@ Later on, this will be checked using this condition:
       Microsoft.AspNetCore.Authentication.Google;
       Microsoft.AspNetCore.Http;
       Microsoft.AspNetCore.Server.IIS;
+      java:signalr;
     </PackagesInPatch>
   </PropertyGroup>
 

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

@@ -454,7 +454,7 @@ public class HubConnection {
      */
     public void send(String method, Object... args) {
         if (hubConnectionState != HubConnectionState.CONNECTED) {
-            throw new RuntimeException("The 'send' method cannot be called if the connection is not active");
+            throw new RuntimeException("The 'send' method cannot be called if the connection is not active.");
         }
 
         InvocationMessage invocationMessage = new InvocationMessage(null, method, args);
@@ -472,6 +472,10 @@ public class HubConnection {
      */
     @SuppressWarnings("unchecked")
     public <T> Single<T> invoke(Class<T> returnType, String method, Object... args) {
+        if (hubConnectionState != HubConnectionState.CONNECTED) {
+            throw new RuntimeException("The 'invoke' method cannot be called if the connection is not active.");
+        }
+
         String id = connectionState.getNextInvocationId();
         InvocationMessage invocationMessage = new InvocationMessage(id, method, args);
 

src/SignalR/clients/java/signalr/src/test/java/com/microsoft/signalr/HubConnectionTest.java

@@ -900,7 +900,16 @@ class HubConnectionTest {
         assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
 
         Throwable exception = assertThrows(RuntimeException.class, () -> hubConnection.send("inc"));
-        assertEquals("The 'send' method cannot be called if the connection is not active", exception.getMessage());
+        assertEquals("The 'send' method cannot be called if the connection is not active.", exception.getMessage());
+    }
+
+    @Test
+    public void cannotInvokeBeforeStart()  {
+        HubConnection hubConnection = TestUtils.createHubConnection("http://example.com");
+        assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
+
+        Throwable exception = assertThrows(RuntimeException.class, () -> hubConnection.invoke(String.class, "inc", "arg1"));
+        assertEquals("The 'invoke' method cannot be called if the connection is not active.", exception.getMessage());
     }
 
     @Test
@@ -1204,4 +1213,4 @@ class HubConnectionTest {
             () -> hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait());
         assertEquals("Unexpected status code returned from negotiate: 500 Internal server error.", exception.getMessage());
     }
-}
+}