Using HttpWebRequest in C# to Send POST and GET Requests to Call APIs

In modern application development, interacting with Web APIs is a fundamental skill. This article will introduce how to use the HttpClient class in C# to send POST and GET requests to call external API services.

Introduction to HttpClient

HttpClient is a class in the .NET Framework and .NET Core used to send HTTP requests and receive HTTP responses. It supports asynchronous operations and can efficiently handle web requests, making it the preferred way for modern C# applications to interact with web services.

Using HttpWebRequest in C# to Send POST and GET Requests to Call APIs

1. Preparation

1. Prepare an API request URL: https://api.qqsuu.cn/api/dm-caipuRequest method: Both GET and POST are acceptableUsing HttpWebRequest in C# to Send POST and GET Requests to Call APIs2. Create a Windows Forms application project. In Visual Studio 2019:

  1. Create a new Windows Forms App (.NET Framework) project

  2. Name it “WindowsFormsPOSTGET”

  3. Design a simple interface that includes:

  • A text box (textBox1) for entering query parameters

  • Two buttons (button1 and button2) to trigger POST and GET requests respectively

  • A rich text box (richTextBox1) to display the API response results

Using HttpWebRequest in C# to Send POST and GET Requests to Call APIs

2. Implementation of GET Request

GET is the most commonly used HTTP method for retrieving data from the server. In our example, the<span><span>Get</span></span> method implements the GET request:

public static string Get(string strUrl){    string str_Output = "";    try    {        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strUrl);        request.Proxy = null;  // Disable proxy        request.Method = "GET";        request.ContentType = "application/json";        HttpWebResponse resp = (HttpWebResponse)request.GetResponse();        using (Stream stream = resp.GetResponseStream())        {            using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))            {                str_Output = reader.ReadToEnd();            }        }        return str_Output;    }    catch (Exception ex)    {        return ex.Message.ToString();    }}

  • Key Points:

  1. <span><span>WebRequest.Create</span></span> creates the request object

  2. Set <span><span>Method</span></span> to “GET” to specify the request type

  3. <span><span>ContentType</span></span> set to “application/json” indicates that JSON format data is expected

  4. Use <span><span>GetResponse</span></span> to get the server response

  5. Read the response content using <span><span>StreamReader</span></span>

Invocation Method:

private void button2_Click(object sender, EventArgs e){    string strUrl = "https://api.qqsuu.cn/api/dm-caipu?word=" + textBox1.Text.Trim();    string strReturn = Get(strUrl);    richTextBox1.Text = strReturn;}

Using HttpWebRequest in C# to Send POST and GET Requests to Call APIs

3. Implementation of POST Request

POST method is typically used to submit data to the server. In our example, the<span><span>Post</span></span> method implements the POST request:

public static string Post(string strUrl){    string str_Output = "";    try    {        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strUrl);        request.Method = "POST";        request.ContentType = "application/json";        // For this specific API, the POST request does not require a request body        using (Stream reqStream = request.GetRequestStream())        {            reqStream.Flush();            reqStream.Close();        }        // Get the response message        HttpWebResponse resp = (HttpWebResponse)request.GetResponse();        Stream stream = resp.GetResponseStream();        // Get the response content        using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))        {            str_Output = reader.ReadToEnd();        }        return str_Output;    }    catch (Exception ex)    {        return ex.Message.ToString();    }}

Key Points:

  1. Set <span><span>Method</span></span> to “POST” to specify the request type

  2. Even if no request body is needed, the request stream must be obtained and closed

  3. The remaining handling is similar to the GET request

Invocation Method:

private void button1_Click(object sender, EventArgs e){    string strUrl = "https://api.qqsuu.cn/api/dm-caipu?word=" + textBox1.Text.Trim();    string strReturn = Post(strUrl);    richTextBox1.Text = strReturn;}

Using HttpWebRequest in C# to Send POST and GET Requests to Call APIs

4. Differences Between GET and POST

  1. Semantic Difference:

  • GET is used to retrieve data

  • POST is used to submit data

  • Parameter Passing:

    • GET parameters are passed via the URL

    • POST parameters are typically passed through the request body

  • Security:

    • GET parameters are visible in the URL and are not suitable for transmitting sensitive information

    • POST parameters are in the request body and are relatively more secure

  • Cache:

    • GET requests can be cached

    • POST requests are typically not cached

    5. Extensions

    1. Sending a POST request with parameters

            public static string PostJson(string strUrl, string jsonInput)        {            string str_Output = "";            try            {                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strUrl);                request.Method = "POST";                request.ContentType = "application/json";                byte[] xmlByte = Encoding.UTF8.GetBytes(jsonInput.ToString());                using (Stream reqStream = request.GetRequestStream())                {                    reqStream.Write(xmlByte, 0, xmlByte.Length);                    reqStream.Flush();                    reqStream.Close();                }                // Get the response message                HttpWebResponse resp = (HttpWebResponse)request.GetResponse();                Stream stream = resp.GetResponseStream();                // Get the response content                using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))                {                    str_Output = reader.ReadToEnd();                }                return str_Output;            }            catch (Exception ex)            {                return ex.Message.ToString();            }        }

    2. Sending a DELETE request with parameters

            public static string DeleteJson(string strUrl, string jsonInput)        {            string str_Output = "";            try            {                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strUrl);                request.Method = "DELETE";                request.ContentType = "application/json";                byte[] xmlByte = Encoding.UTF8.GetBytes(jsonInput.ToString());                using (Stream reqStream = request.GetRequestStream())                {                    reqStream.Write(xmlByte, 0, xmlByte.Length);                    reqStream.Flush();                    reqStream.Close();                }                // Get the response message                HttpWebResponse resp = (HttpWebResponse)request.GetResponse();                Stream stream = resp.GetResponseStream();                // Get the response content                using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))                {                    str_Output = reader.ReadToEnd();                }                return str_Output;            }            catch (Exception ex)            {                return "";            }        }

    6. Considerations in Practical Applications

    1. Error Handling: As shown in the example, potential network exceptions should be handled properly

    2. Asynchronous Calls: In practical applications, consider using asynchronous methods to avoid freezing the interface

    3. Parameter Encoding: Parameters in the URL should be encoded, which can be done using <span><span>System.Web.HttpUtility.UrlEncode</span></span>

    4. Request Timeout: The <span><span>Timeout</span></span> property can be set to control the request timeout duration

    5. HTTPS Support: Most modern APIs use HTTPS, which is supported by .NET by default

    Conclusion

    Through this simple example, we have demonstrated the basic methods of calling APIs using POST and GET in C#. Although the example uses Windows Forms, the core code for these network requests is also applicable to other types of .NET applications such as WPF and console applications. With an understanding of these fundamentals, you can further explore more complex API interaction scenarios.

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