Android以Java语言向ASP.net Web API发送POST请求

Android以Java语言向ASP.NET Web API发送POST请求

基础概念

在Android应用中向ASP.NET Web API发送POST请求是一种常见的跨平台通信方式，涉及客户端(Android)与服务器端(ASP.NET)之间的HTTP交互。POST请求通常用于向服务器提交数据，如用户登录信息、表单数据等。

实现方式

1. 使用HttpURLConnection

public class HttpPostRequest {
    public static String sendPost(String urlStr, String jsonInputString) throws IOException {
        URL url = new URL(urlStr);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        
        // 设置请求方法为POST
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "application/json");
        connection.setRequestProperty("Accept", "application/json");
        connection.setDoOutput(true);
        
        // 发送请求数据
        try(OutputStream os = connection.getOutputStream()) {
            byte[] input = jsonInputString.getBytes("utf-8");
            os.write(input, 0, input.length);           
        }
        
        // 获取响应
        try(BufferedReader br = new BufferedReader(
            new InputStreamReader(connection.getInputStream(), "utf-8"))) {
            StringBuilder response = new StringBuilder();
            String responseLine;
            while ((responseLine = br.readLine()) != null) {
                response.append(responseLine.trim());
            }
            return response.toString();
        }
    }
}

2. 使用OkHttp (推荐)

首先在build.gradle中添加依赖：

implementation 'com.squareup.okhttp3:okhttp:4.9.3'

然后实现POST请求：

public class OkHttpPostRequest {
    private final OkHttpClient client = new OkHttpClient();
    
    public String post(String url, String json) throws IOException {
        RequestBody body = RequestBody.create(json, MediaType.get("application/json"));
        Request request = new Request.Builder()
                .url(url)
                .post(body)
                .build();
        
        try (Response response = client.newCall(request).execute()) {
            if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
            return response.body().string();
        }
    }
}

3. 使用Volley

首先在build.gradle中添加依赖：

implementation 'com.android.volley:volley:1.2.1'

然后实现POST请求：

public class VolleyPostRequest {
    public void postRequest(Context context, String url, String requestBody) {
        RequestQueue queue = Volley.newRequestQueue(context);
        
        StringRequest stringRequest = new StringRequest(Request.Method.POST, url,
                response -> {
                    // 处理成功响应
                    Log.d("Response", response);
                },
                error -> {
                    // 处理错误
                    Log.e("Error", error.toString());
                }) {
            @Override
            public byte[] getBody() {
                return requestBody.getBytes(StandardCharsets.UTF_8);
            }
            
            @Override
            public String getBodyContentType() {
                return "application/json";
            }
        };
        
        queue.add(stringRequest);
    }
}

ASP.NET Web API端示例

[Route("api/[controller]")]
[ApiController]
public class SampleController : ControllerBase
{
    [HttpPost]
    public IActionResult Post([FromBody] UserModel user)
    {
        if (user == null)
        {
            return BadRequest();
        }
        
        // 处理接收到的数据
        return Ok(new { Message = "Data received", User = user });
    }
}

public class UserModel
{
    public string Username { get; set; }
    public string Password { get; set; }
}

常见问题及解决方案

1. 连接超时

原因：网络不稳定或服务器响应慢解决：

设置合理的超时时间
检查网络连接
在OkHttp中：client.newBuilder().connectTimeout(10, TimeUnit.SECONDS).build()

2. 400 Bad Request

原因：请求格式不正确或缺少必要参数解决：

检查请求头是否正确设置了Content-Type
确保JSON数据格式正确
验证ASP.NET API端模型绑定是否正确

3. 415 Unsupported Media Type

原因：Content-Type与服务器期望的不匹配解决：

确保客户端和服务器使用相同的Content-Type
在Android端正确设置请求头：connection.setRequestProperty("Content-Type", "application/json")

4. 跨域问题(CORS)

原因：浏览器安全策略阻止跨域请求解决：

在ASP.NET端启用CORS：

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddCors(options =>
    {
        options.AddPolicy("AllowAll",
            builder => builder.AllowAnyOrigin()
                            .AllowAnyMethod()
                            .AllowAnyHeader());
    });
    
    services.AddControllers();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseCors("AllowAll");
    // 其他中间件...
}