Atmosphere fallback功能异常：服务器发数据客户端无法接收求助

Hey Sebastian, sorry to hear you're hitting this snag with the long-polling fallback in older browsers. Let's break down some key areas to check that might resolve the issue where your client isn't receiving messages even though the server is writing to the AtmosphereResource.

1. Verify Server-Side Message Handling & Response Configuration #

• Ensure proper flushing of messages: When writing to AtmosphereResource, make sure you're explicitly flushing the response after sending messages. Long-polling relies on the response being completed (or flushed properly) for the client to detect the message, unlike SSE which streams incrementally. Example:

  resource.write(message).flush();
  

• Check Content-Type consistency: Confirm the response uses the correct Content-Type (matching your client's contentType: "application/json" setting). Older browsers can be strict about this, so avoid accidental overrides from Spring/Struts filters.

2. Rule Out Struts2 Interceptor Conflicts #

Struts2 interceptors might interfere with Atmosphere's long-polling requests, especially since you're using a POST method. Try excluding your Atmosphere endpoint from Struts2 processing:

• Add this constant to your struts.xml:

  <constant name="struts.action.excludePattern" value="/public/sse/.*"/>
  

  This ensures the request reaches Atmosphere's servlet directly without being modified by Struts2's request processing chain.

3. Align Atmosphere Dependency Versions #

You're using atmosphere-runtime 2.4.24 but atmosphere-spring 2.4.20—version mismatches can cause subtle compatibility issues around Spring's integration with Atmosphere's async handling. Update your atmosphere-spring dependency to match the runtime version (2.4.24) and retest.

4. Confirm Client-Side Callback Setup #

Double-check that your client code has a properly bound onMessage callback—without it, you won't see incoming messages even if they're received:

request.onMessage = function(response) {
    console.log("Received message:", response.responseBody);
    // Add your message processing logic here
};

// Initialize the connection
var socket = atmosphere.subscribe(request);

Also, ensure you're not accidentally overriding the callback elsewhere in your code.

5. Address IE/Edge-Specific Behavior #

Older Microsoft browsers have unique quirks that can break long-polling:

• Disable caching: Add headers to prevent IE from caching the long-poll response:

  request.headers = { 'Cache-Control': 'no-cache', 'Pragma': 'no-cache' };
  

• Check async servlet support: Make sure your AtmosphereServlet in web.xml has <async-supported>true</async-supported> enabled—Tomcat requires this for async long-polling, and IE/Edge can fail silently if this is missing.
• Response size limits: IE has stricter limits on AJAX response sizes. If your messages are large, try splitting them into smaller chunks or verify they don't exceed IE's maximum allowed size.

内容的提问来源于stack exchange，提问作者Sebastian Götz