Asp.net core 學習筆記 ( HttpClient )

2018-09-18

core 2.1 以後有新的方案咯

http://www.talkingdotnet.com/3-ways-to-use-httpclientfactory-in-asp-net-core-2-1/

就是解決以前單列等等的問題.

給個例子 

定義一個 service

public class ServerTaskHttpClient
{
    public HttpClient Client { get; private set; }

    public ServerTaskHttpClient(
        HttpClient httpClient,
        IConfiguration configuration
    )
    {
        httpClient.BaseAddress = new Uri(configuration["Origin"] + "/api");
        httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(MediaTypeNames.Application.Json));
　　　　 // httpClient.DefaultRequestHeaders.Add(HeaderNames.ContentType, MediaTypeNames.Application.Json);  //注意, 放這裏是錯的, content-type 不是這裏 set 的，而是經過 content
        Client = httpClient;
    }
}

startup.cs 

加入依賴 providers

 services.AddHttpClient<ServerTaskHttpClient>();

在 controller 調用

public class ResponseData {
    public bool successful { get; set; }
}
public async Task<IActionResult> Index()
{
    var content = new StringContent(JsonConvert.SerializeObject(new { name = "dada" }), Encoding.UTF8, MediaTypeNames.Application.Json);
    var result = await ServerTaskHttpClient.Client.PostAsync("/api/debug/clearImage", content);
    if (result.IsSuccessStatusCode)
    {
        var responseData = JsonConvert.DeserializeObject<ResponseData>(await result.Content.ReadAsStringAsync());
    }
    return View();
}

api 

[HttpPost("clearImage")]
public async Task<IActionResult> ClearImage(Data data)
{
    return Ok(new { successful = true });
}

 

 

 

 

 

2017-09-25 

core 和 .net 4.5 同樣均可以使用 HttpClient 

沒什麼特別的, 只是在學習的時候發現一個以前沒留意到的問題. 

refer : 

https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/

http://byterot.blogspot.my/2016/07/singleton-httpclient-dns.html

http://www.cnblogs.com/dudu/p/csharp-httpclient-attention.html

https://docs.microsoft.com/en-us/aspnet/web-api/overview/advanced/calling-a-web-api-from-a-net-client

http://www.cnblogs.com/Wddpct/p/6229090.html

大體上說的是, HttpClient 不要使用 using, 由於它並不會釋放 TCP 鏈接, 應該在整個應用裏把 HttpClient 設置成單列 

 

core 要設置單列對象很容易 

public class VisautoHttpClient : HttpClient
{
    public VisautoHttpClient()
    {
        BaseAddress = new Uri("http://visauto.stooges.com.my");
        Timeout = TimeSpan.FromSeconds(30);
        DefaultRequestHeaders.Clear();
        DefaultRequestHeaders.Add("Accept", "text/html");
        DefaultRequestHeaders.Connection.Add("Keep-Alive"); 
    } 
}

定義好類, 因爲每一個 TCP 的 baseAddress 不能換的，因此若是你有不少個不一樣區的請求要發, 那麼建議開多幾個 HttpClient 實例.

keep-alive 的目的是讓服務端知道咱們的鏈接不要立刻斷開, 這樣發多個請求的話能夠快一些. 

而後在 startup.cs 提供服務就能夠了. 

public void ConfigureServices(IServiceCollection services)
{ 
    // services 
    services.AddSingleton<VisautoHttpClient, VisautoHttpClient>();
}

core 會幫咱們搞定 singleton 的線程安全等問題. 不須要像從前還要用 lock 什麼的那麼麻煩了.

並且這裏只是定義，一直到控制器注入時纔會初始化實例哦.

在控制器注入了就能夠發請求咯~

[Area("Web")]
public class HttpController : Controller
{
    public HttpController(
        VisautoHttpClient httpClient 
    )
    {
        this.httpClient = httpClient;
    }

    private HttpClient httpClient { get; set; }
        

    [Route("http")]
    public async Task<IActionResult> Index()
    {
        try
        {
            string x = await httpClient.GetStringAsync("");
        }
        catch (Exception ex)
        {

        }
        return View();
    }
}

 

note : 若是服務器 restart, 咱們的鏈接並不須要任何處理, 都是自動的. 放心, dns 的問題我沒有遇到, 遇到了纔打算唄.