如何在 Jetty 中设置多个处理程序并且在启动过程中不会出错

Question

I have some server code which looks like this:

private WebAppContext getAspireWebAppContext() {
    WebAppContext root = new WebAppContext();
    root.setWar(config().<String>property("war.file"));
    root.setContextPath("/");
    return root;
}

private Server startWebApp(int port) {
  try {
    server.setConnectors(createConnectors(port));
    ServletContextHandler context = getAspireWebAppContext();
    server.setHandler(context);

    // Ensure that a websocket always has a HttpSession
    context.addFilter(HttpSessionForWebsocketFilter.class,"/ws/*",null);
    // add websocket support
    ServerContainer wscontainer = WebSocketServerContainerInitializer.configureContext( context );
    wscontainer.addEndpoint(EngineSocket.class);
    wscontainer.addEndpoint(WorkbenchSocket.class);

    server.start();
  } ....
}

I want to use a HandlerList so I can add a RewriteHandler. So I tried to change it:

HandlerList handlers = new HandlerList();

server.setConnectors(createConnectors(port));
ServletContextHandler context = getAspireWebAppContext();
// server.setHandler(context);
handlers.addHandler(context);

// Ensure that a websocket always has a HttpSession
context.addFilter(HttpSessionForWebsocketFilter.class,"/ws/*",null);
// add websocket support
ServerContainer wscontainer = WebSocketServerContainerInitializer.configureContext( context );
wscontainer.addEndpoint(EngineSocket.class);
wscontainer.addEndpoint(WorkbenchSocket.class);

// RewriteHandler stuff
// handlers.addHandler(rewrite);

server.setHandler(handlers);
server.start();

Even before I add any more handlers this causes a null exception on the WebSocketServerContainerInitializer.configureContext(context) line:

Caused by: java.lang.NullPointerException at org.eclipse.jetty.websocket.jsr356.server.deploy.WebSocketServerContainerInitializer.configureContext(WebSocketServerContainerInitializer.java:148)

I read somewhere that context.setServer(server); might help but to no avail. What am I doing wrong? Thanks

Answer 1

Add the HandlerList to the server first.

Server server = new Server();
HandlerList handlers = new HandlerList();
server.setHandler(handlers);

ServletContextHandler context = getAspireWebAppContext();
handlers.addHandler(context);

ServerContainer wscontainer = WebSocketServerContainerInitializer.configureContext( context );
wscontainer.addEndpoint(EngineSocket.class);
wscontainer.addEndpoint(WorkbenchSocket.class);

// RewriteHandler stuff
handlers.addHandler(rewrite);

server.start();

But ultimately, this NPE is a bug with an internal attempt to fetch a common HttpClient from the Server that belongs to your ServletContextHandler .

Opened as https://github.com/eclipse/jetty.project/issues/3139

Also of note, you should know that you cannot apply filters to WebSocket connections reliably.

WebSocket upgrades via JSR356 (the API you are choosing to use) is designed to do the upgrade outside of the Filter chain. This is because a Filter can modify the request/response, change commit state of the response, wrap input streams, wrap output streams, etc. All of which are forbidden during a WebSocket upgrade. While your Filter might work some of the time, it will not work 100% of the time. And the Set-Cookie header from such an action isn't guaranteed to be sent back on the response either.

If you switch to the Jetty Native WebSocket API you can control where the upgrade occurs (same forbidden actions apply). Extend from WebSocketServlet , or extend from WebSocketUpgradeFilter and apply your own logic, or even better, supply your own WebSocketCreator to do what you need.