TooTallNate/Java-WebSocket · error · IllegalArgumentException

This websocket uses ws instead of wss. No SSLSession…

Error message

This websocket uses ws instead of wss. No SSLSession available.

What it means

This is a pre-condition guard in WebSocketClient.getSSLSession: the method can only return an SSLSession when the underlying socket is an SSLSocket (i.e. the connection used the wss:// scheme). For a plain ws:// connection there is no TLS layer and therefore no session to expose, so the library throws rather than returning null. The faulty input is calling getSSLSession() (often indirectly through code that assumes TLS) on a websocket that was opened with ws instead of wss.

Solutions

1. Check hasSSLSupport() before calling getSSLSession() and skip or branch when it returns false
2. Use a wss:// URI (with proper SSLContext/SSLSocketFactory configuration) if an SSLSession is actually required
3. Refactor caller code to not require TLS metadata when the connection is plain ws
4. Wrap the call in a try-catch for IllegalArgumentException if the ws/wss scheme is determined at runtime

When it happens

Trigger: Thrown at src/main/java/org/java_websocket/client/WebSocketClient.java:1003 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of TooTallNate/Java-WebSocket@afeacbf8c0 (2026-09-09). Data as JSON: /api/errors/824b08608323c625. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/org/java_websocket/client/WebSocketClient.java:1003

  @Override
  public InetSocketAddress getRemoteSocketAddress() {
    return engine.getRemoteSocketAddress();
  }

  @Override
  public String getResourceDescriptor() {
    return uri.getPath();
  }

  @Override
  public boolean hasSSLSupport() {
    return socket instanceof SSLSocket;
  }

  @Override
  public SSLSession getSSLSession() {
    if (!hasSSLSupport()) {
      throw new IllegalArgumentException(
          "This websocket uses ws instead of wss. No SSLSession available.");
    }
    return ((SSLSocket)socket).getSession();
  }

  @Override
  public IProtocol getProtocol() {
    return engine.getProtocol();
  }

  /**
   * Method to give some additional info for specific IOExceptions
   *
   * @param e the IOException causing a eot.
   */
  private void handleIOException(IOException e) {
    if (e instanceof SSLException) {
      onError(e);

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