[JAVA] Autowired fields in a class that inherits TextWebSocketHandler in Spring Boot become NULL

1. Environment

Spring Boot：v2.2.5

2. Trouble

Use WebSocket to create a chat function with Spring Boot.

I created a class that inherits from TextWebSocketHandler and tried to Autowired the repository class to access the DB in it, but the repository class variable declared in the field is NULL.

The following is the WebSocketChatEndpoint class that inherits from TextWebSocketHandler.

WebSocketChatEndpoint.java

@ServerEndpoint("/api/chat")
@Component
public class WebSocketChatEndpoint extends TextWebSocketHandler {

  @Autowired
  private ChatRepository chatRepository; //NULL

  @OnOpen
  public void onOpen(Session session) {
… Abbreviation

At run time, chatRepository is NULL.

3. Correspondence

Changed field injection to setter injection.

WebSocketChatEndpoint.java

@ServerEndpoint("/api/chat")
@Component
public class WebSocketChatEndpoint extends TextWebSocketHandler {

  private static ChatRepository chatRepository; //Autowired

  @Autowired
  public void setChatRepository (ChatRepository chatRepository ) {
        WebSocketChatEndpoint.chatRepository = chatRepository;
  }

  @OnOpen
  public void onOpen(Session session) {
… Abbreviation

I haven't tried constructor injection.