Web API 2中POST请求返回404错误，但GET请求正常，求排查原因

Hey there! Let's figure out why your POST request is returning a 404 while GET works perfectly. Here are the most common issues to check, along with fixes:

1. Mismatched Route Configuration #

First, double-check your controller and POST method routing attributes. If your controller uses [Route("api/[controller]")], make sure your POST method has the correct [HttpPost] attribute (with or without a specific route template).

For example:

[ApiController]
[Route("api/[controller]")]
public class MyApiController : ControllerBase
{
    // Correct basic POST setup
    [HttpPost] // Matches POST to api/myapi
    public IActionResult Post([FromBody] RequestModel model)
    {
        // Your logic here
        return Ok();
    }

    // Or if you need a parameter in the route
    [HttpPost("{appKey}")] // Matches POST to api/myapi/your-app-key
    public IActionResult Post(string appKey)
    {
        // Your logic here
        return Ok();
    }
}

If your POST method is missing the [HttpPost] attribute entirely, ASP.NET won't map it to POST requests, leading to a 404.

2. Incorrect Request Content Type or Parameter Binding #

When using Postman, make sure you're sending the request in a format your API expects:

• If your method uses [FromBody] to accept JSON data, set the Content-Type header to application/json and paste valid JSON in the request body.
• If you're passing form data, use application/x-www-form-urlencoded or multipart/form-data instead.
• Don't forget to add [FromBody], [FromForm], or [FromQuery] attributes to your method parameters if needed—without these, ASP.NET might not know where to pull the data from, causing routing to fail.

3. Typos or Path Mismatches #

It sounds silly, but even a small typo in your Postman request path can cause a 404. Check:

• The controller name in the path (e.g., if your controller is ProductController, the route should include api/product).
• Any route parameters (like appKey) are included in the correct position (either in the URL path or query string, depending on your method's setup).
• Case sensitivity—while ASP.NET Core is case-insensitive by default, some hosting environments or custom routing constraints might change this.

4. Missing Routing Middleware in Startup #

Double-check your Program.cs (or Startup.cs) to ensure you've set up routing correctly. You need these two lines in your pipeline:

app.UseRouting();

app.UseEndpoints(endpoints =>
{
    endpoints.MapControllers(); // This maps attribute-routed controllers
});

Without MapControllers(), your API won't register any controller routes—so POST (and all other) requests will return 404.

5. Enable Detailed Routing Logs #

If you're still stuck, turn on debug logging for routing to see exactly what's happening when your request comes in. Update your appsettings.json:

{
  "Logging": {
    "LogLevel": {
      "Microsoft.AspNetCore.Routing": "Debug"
    }
  }
}

Run your app and send the POST request again—you'll see detailed logs in the console showing which routes ASP.NET tried to match, and why it couldn't find a match for your request. This is usually the fastest way to pinpoint the issue.

内容的提问来源于stack exchange，提问作者jleach