RESTlet本地XHR请求失败：直接访问URL正常

Let’s work through this frustrating issue you’re facing—direct URL access works, mobile requests over SSH port forwarding work, but local Dojo XHR calls keep throwing that status 0 error. Here’s a breakdown of the most likely causes and actionable fixes:

First, Let’s Recap Your Problem #

Directly visiting http://localhost:8080/asWeb/r/WebVersion returns valid JSON. Mobile Dojo XHR requests work perfectly via SSH port forwarding, but local requests fail with:

STATUS: 0 (RequestError: Unable to load http://localhost:8080/asWeb/r/WebVersion status: 0)
message: "Unable to load /asWeb/r/Login status: 0"

1. You’re Running the Frontend via file:// Protocol (Most Common Fix) #

If you’re opening your local HTML file directly in the browser (like double-clicking it), you’re using the file:// protocol. Browsers enforce strict same-origin policy here, which blocks requests to http://localhost:8080—since file:// and http:// are considered completely separate origins. The mobile setup avoids this because the app is likely running in a web view or on a server that aligns with the forwarded endpoint’s origin.

Fix:
Host your frontend files on a local web server instead of using file://. Easy options include:

• Use a simple Node.js server: Install http-server via npm (npm install -g http-server), run http-server in your frontend folder, and access it at http://localhost:8081 (or another free port).
• Use Apache/Nginx if you already have them set up.
• This ensures your frontend runs on the http:// protocol, matching your backend’s protocol and resolving same-origin conflicts.

2. Missing CORS Configuration in RESTlet #

Even on localhost, requests between different ports (e.g., frontend on 8081, backend on 8080) trigger cross-origin resource sharing (CORS) checks. Mobile web views often have looser policies, but desktop browsers enforce this strictly.

Fix:
Add a CORS filter to your RESTlet application to explicitly allow cross-origin requests:

import org.restlet.ext.cors.CorsFilter;
import org.restlet.Application;
import org.restlet.Restlet;
import org.restlet.routing.Router;

public class YourWebApplication extends Application {
    @Override
    public Restlet createInboundRoot() {
        Router router = new Router(getContext());
        // Add your existing route configurations here (e.g., /asWeb/r/WebVersion, /asWeb/r/Login)
        
        // Set up CORS filter
        CorsFilter corsFilter = new CorsFilter(getContext(), router);
        corsFilter.setAllowedOrigins("*"); // Replace with specific origins (like http://localhost:8081) for production
        corsFilter.setAllowedMethods("GET,POST,PUT,DELETE,OPTIONS");
        corsFilter.setAllowedHeaders("Content-Type,Authorization");
        
        return corsFilter;
    }
}

This tells your RESTlet backend to send the necessary headers to permit frontend requests from different ports.

3. Browser Plugins or Security Settings Blocking the Request #

Desktop browser extensions like ad blockers, privacy tools, or antivirus software sometimes intercept local XHR requests, resulting in a status 0 error with no clear explanation.

Fix:

• Test your request in the browser’s incognito/private mode (plugins are disabled by default here).
• Temporarily turn off all browser extensions and re-run the request.
• Check the browser’s DevTools console (F12 > Console tab) for hidden error messages about blocked requests.

4. Double-Check Your Request Path #

The error mentions /asWeb/r/Login but you tested /asWeb/r/WebVersion—make sure your Dojo code’s request path is accurate. If you’re using a relative path, it might resolve incorrectly based on your frontend’s URL structure.

Fix:
Use the full absolute URL in your Dojo XHR call to avoid path confusion:

dojo.xhrGet({
    url: "http://localhost:8080/asWeb/r/WebVersion",
    handleAs: "json",
    load: function(response) {
        console.log("Success:", response);
    },
    error: function(err) {
        console.error("Error:", err);
    }
});

内容的提问来源于stack exchange，提问作者user3260912