android - 在 Android 中调用 .NET Web API Post Service 发送空消息

Question

我在 ASP.net 端实现了一个 Web API 服务，并想从 Android 调用它，但发送的消息为空“类型已成功上传:!”。发送的数据应打印在冒号和感叹号之间。 我还检查了数据库，添加了一个带有空值的类型。我还检查了 Fiddler 上的 Web API，当我发送字符串值时它可以正常工作。那么如何才能正确发送数据呢？提前致谢。

ASP.net端

[HttpPost]
    public String SetType([FromBody]string type)
    {
        SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["MConnectionString"].ConnectionString);
        try
        {
            connection.Open();
            SqlCommand cmd = new SqlCommand("insert into [MeasureType] (type_name) values (' " + type + " ')", connection);
            cmd.ExecuteNonQuery();

            return "type has been uploaded successfully : " + type + " !";
        }
        catch (Exception exception)
        {
            return exception.Message + "error uploading type";
        }
        finally
        {
            connection.Close();
        }

    }

Android端

public String SetMeasureType(String type)
{
    java.net.URL url = null;
    StringBuilder builder = new StringBuilder();
    HttpURLConnection connection = null;
    try {
        url = new URL("http://192.168.1.140:65079/api/monitoringtool/SetType");
        // open a connection
        connection = (HttpURLConnection) url.openConnection();

        connection.setDoInput(true); // to get request only
        connection.setDoOutput(true); // upload a request body
        connection.setUseCaches(false);
        connection.setRequestMethod("POST"); // request method post
        connection.setRequestProperty("Content-Type", "application/json");
        connection.setRequestProperty("Content-Length","" + Integer.toString(type.getBytes().length));
        connection.setRequestProperty("Content-Language", "en-US");
        connection.setConnectTimeout(3000); // connection time out
        connection.setReadTimeout(3000); // read time out

        // Send request
        OutputStream outStream = new BufferedOutputStream(connection.getOutputStream());
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(outStream, "UTF-8"));
        writer.write(type);
        writer.flush();
        writer.close();
        outStream.close();

        // get response
        InputStream inStream = connection.getInputStream(); // input stream of connection to get data
        BufferedReader reader = new BufferedReader(new InputStreamReader(inStream)); // reader for reading data from stream
        String line;
        while((line = reader.readLine()) != null)
        {
            builder.append(line);
        }
        int responseCode = connection.getResponseCode();
        reader.close();
        if(responseCode == HttpURLConnection.HTTP_OK)
        {
            return builder.toString();
        }

    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    finally {
        if (connection != null) {
            connection.disconnect();
        }
    }
    return builder.toString();
}

Answer 1

有两件事，

在 Android 端发送实际的 JSON 字符串

//...

//construct JSON
String json = "{\"type\":\"" + type + "\"}";
connection.setRequestProperty("Content-Length","" + Integer.toString(json.getBytes().length));
//send 
writer.write(json);

//...

在 ASP.net Web API 端，

创建一个模型来表示要接收的数据

public class TypeModel {
    public string type { get; set; }
}

并更新 ApiController 操作以期望模型

[HttpPost]
public IHttpActionResult SetType([FromBody]TypeModel model) {

    if (!ModelState.IsValid) return BadRequest(ModelState);

    var connectionString = ConfigurationManager.ConnectionStrings["MConnectionString"].ConnectionString;
    using (var connection = new SqlConnection(connectionString)) {
        try {
            var type = model.type;
            connection.Open();
            var cmd = new SqlCommand("insert into [MeasureType] (type_name) values (@type)", connection);

            var parameter = cmd.CreateParameter();
            parameter.ParameterName = "@type";
            parameter.Value = type;

            cmd.Parameters.Add(parameter);

            return Ok("type has been uploaded successfully : " + type + " !");
        } catch (Exception exception) {
            return InternalServerError(exception);
        }
    }
}

还要注意参数的使用以避免 SQL 注入(inject)。