simplify websocket session retrieval

commafeed-server/src/main/java/com/commafeed/frontend/ws/WebSocketSessions.java

@@ -3,7 +3,6 @@ package com.commafeed.frontend.ws;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.stream.Collectors;
 
 import com.codahale.metrics.Gauge;
 import com.codahale.metrics.MetricRegistry;
@@ -38,12 +37,7 @@ public class WebSocketSessions {
 	}
 
 	public void sendMessage(User user, String text) {
-		Set<Session> userSessions = sessions.entrySet()
+		Set<Session> userSessions = sessions.get(user.getId());
-				.stream()
-				.filter(e -> e.getKey().equals(user.getId()))
-				.flatMap(e -> e.getValue().stream())
-				.collect(Collectors.toSet());
-
 		if (!userSessions.isEmpty()) {
 			log.debug("sending '{}' to {} users via websocket", text, userSessions.size());
 			for (Session userSession : userSessions) {

commafeed-server/src/test/java/com/commafeed/frontend/ws/WebSocketSessionsTest.java

@@ -0,0 +1,82 @@
+package com.commafeed.frontend.ws;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Answers;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import com.codahale.metrics.MetricRegistry;
+import com.commafeed.backend.model.User;
+
+import jakarta.websocket.Session;
+
+@ExtendWith(MockitoExtension.class)
+class WebSocketSessionsTest {
+
+	@Mock
+	private MetricRegistry metrics;
+
+	@Mock(answer = Answers.RETURNS_DEEP_STUBS)
+	private Session session1;
+
+	@Mock(answer = Answers.RETURNS_DEEP_STUBS)
+	private Session session2;
+
+	@Mock(answer = Answers.RETURNS_DEEP_STUBS)
+	private Session session3;
+
+	private WebSocketSessions webSocketSessions;
+
+	@BeforeEach
+	void init() {
+		webSocketSessions = new WebSocketSessions(metrics);
+	}
+
+	@Test
+	void sendsMessageToUser() {
+		Mockito.when(session1.isOpen()).thenReturn(true);
+		Mockito.when(session2.isOpen()).thenReturn(true);
+
+		User user1 = newUser(1L);
+		webSocketSessions.add(user1.getId(), session1);
+		webSocketSessions.add(user1.getId(), session2);
+
+		User user2 = newUser(2L);
+		webSocketSessions.add(user2.getId(), session3);
+
+		webSocketSessions.sendMessage(user1, "Hello");
+		Mockito.verify(session1).getAsyncRemote();
+		Mockito.verify(session2).getAsyncRemote();
+		Mockito.verifyNoInteractions(session3);
+	}
+
+	@Test
+	void closedSessionsAreNotNotified() {
+		Mockito.when(session1.isOpen()).thenReturn(false);
+
+		User user1 = newUser(1L);
+		webSocketSessions.add(user1.getId(), session1);
+
+		webSocketSessions.sendMessage(user1, "Hello");
+		Mockito.verify(session1, Mockito.never()).getAsyncRemote();
+	}
+
+	@Test
+	void removedSessionsAreNotNotified() {
+		User user1 = newUser(1L);
+		webSocketSessions.add(user1.getId(), session1);
+		webSocketSessions.remove(session1);
+
+		webSocketSessions.sendMessage(user1, "Hello");
+		Mockito.verifyNoInteractions(session1);
+	}
+
+	private User newUser(Long userId) {
+		User user = new User();
+		user.setId(userId);
+		return user;
+	}
+}