Update HubConnection url in Java client (#11010)

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

@@ -29,7 +29,7 @@ public class HubConnection {
     private static final List<Class<?>> emptyArray = new ArrayList<>();
     private static final int MAX_NEGOTIATE_ATTEMPTS = 100;
 
-    private final String baseUrl;
+    private String baseUrl;
     private Transport transport;
     private OnReceiveCallBack callback;
     private final CallbackMap handlers = new CallbackMap();
@@ -288,6 +288,27 @@ public class HubConnection {
         return hubConnectionState;
     }
 
+    // For testing only
+    String getBaseUrl() {
+        return this.baseUrl;
+    }
+
+    /**
+     * Sets a new url for the HubConnection.
+     * @param url The url to connect to.
+     */
+    public void setBaseUrl(String url) {
+        if (url == null || url.isEmpty()) {
+            throw new IllegalArgumentException("The HubConnection url must be a valid url.");
+        }
+
+        if (hubConnectionState != HubConnectionState.DISCONNECTED) {
+            throw new IllegalStateException("The HubConnection must be in the disconnected state to change the url.");
+        }
+
+        this.baseUrl = url;
+    }
+
     /**
      * Starts a connection to the server.
      *

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

@@ -106,6 +106,82 @@ class HubConnectionTest {
         assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
     }
 
+    @Test
+    public void hubConnectionUrlCanBeChanged() {
+        MockTransport mockTransport = new MockTransport();
+        HubConnection hubConnection = TestUtils.createHubConnection("http://example.com", mockTransport);
+
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals(HubConnectionState.CONNECTED, hubConnection.getConnectionState());
+        assertEquals("http://example.com", hubConnection.getBaseUrl());
+
+        hubConnection.stop().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
+
+        hubConnection.setBaseUrl("http://newurl.com");
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals("http://newurl.com", hubConnection.getBaseUrl());
+
+        hubConnection.stop().timeout(1, TimeUnit.SECONDS).blockingAwait();
+    }
+
+    @Test
+    public void canUpdateUrlInOnClosed() {
+        MockTransport mockTransport = new MockTransport();
+        HubConnection hubConnection = TestUtils.createHubConnection("http://example.com", mockTransport);
+
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals(HubConnectionState.CONNECTED, hubConnection.getConnectionState());
+        assertEquals("http://example.com", hubConnection.getBaseUrl());
+
+        hubConnection.onClosed((error) -> {
+            hubConnection.setBaseUrl("http://newurl.com");
+        });
+
+        hubConnection.stop().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals(HubConnectionState.DISCONNECTED, hubConnection.getConnectionState());
+
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals("http://newurl.com", hubConnection.getBaseUrl());
+
+        hubConnection.stop().timeout(1, TimeUnit.SECONDS).blockingAwait();
+    }
+
+    @Test
+    public void changingUrlWhenConnectedThrows() {
+        MockTransport mockTransport = new MockTransport();
+        HubConnection hubConnection = TestUtils.createHubConnection("http://example.com", mockTransport);
+
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals(HubConnectionState.CONNECTED, hubConnection.getConnectionState());
+        assertEquals("http://example.com", hubConnection.getBaseUrl());
+
+
+        Throwable exception = assertThrows(IllegalStateException.class, () -> hubConnection.setBaseUrl("http://newurl.com"));
+        assertEquals("The HubConnection must be in the disconnected state to change the url.",exception.getMessage());
+    }
+
+    @Test
+    public void settingNewUrlToNullThrows() {
+        MockTransport mockTransport = new MockTransport();
+        HubConnection hubConnection = TestUtils.createHubConnection("http://example.com", mockTransport);
+
+        hubConnection.start().timeout(1, TimeUnit.SECONDS).blockingAwait();
+
+        assertEquals(HubConnectionState.CONNECTED, hubConnection.getConnectionState());
+        assertEquals("http://example.com", hubConnection.getBaseUrl());
+
+        Throwable exception = assertThrows(IllegalArgumentException.class, () -> hubConnection.setBaseUrl(null));
+        assertEquals("The HubConnection url must be a valid url.",exception.getMessage());
+    }
+
     @Test
     public void invalidHandShakeResponse() {
         MockTransport mockTransport = new MockTransport(false);