C#中HttpWebRequest、WebClient、HttpClient的使用详解 [操作系统入门]
HttpWebRequest:
命名空间: System.Net,这是.NET创建者最初开发用于使用HTTP请求的标准类。使用HttpWebRequest可以让开发者控制请求/响应流程的各个方面,如 timeouts, cookies, headers, protocols。另一个好处是HttpWebRequest类不会阻塞UI线程。例如,当您从响应很慢的API服务器下载大文件时,您的应用程序的UI不会停止响应。HttpWebRequest通常和WebResponse一起使用,一个发送请求,一个获取数据。HttpWebRquest更为底层一些,能够对整个访问过程有个直观的认识,但同时也更加复杂一些。
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//POST方法
public
static
string
HttpPost(
string
Url,
string
postDataStr)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
request.Method =
"POST"
;
request.ContentType =
"application/x-www-form-urlencoded"
;
Encoding encoding = Encoding.UTF8;
byte
[] postData = encoding.GetBytes(postDataStr);
request.ContentLength = postData.Length;
Stream myRequestStream = request.GetRequestStream();
myRequestStream.Write(postData, 0, postData.Length);
myRequestStream.Close();
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream myResponseStream = response.GetResponseStream();
StreamReader myStreamReader =
new
StreamReader(myResponseStream, encoding);
string
retString = myStreamReader.ReadToEnd();
myStreamReader.Close();
myResponseStream.Close();
return
retString;
}
//GET方法
public
static
string
HttpGet(
string
Url,
string
postDataStr)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url + (postDataStr ==
""
?
""
:
"?"
) + postDataStr);
request.Method =
"GET"
;
request.ContentType =
"text/html;charset=UTF-8"
;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream myResponseStream = response.GetResponseStream();
StreamReader myStreamReader =
new
StreamReader(myResponseStream, Encoding.GetEncoding(
"utf-8"
));
string
retString = myStreamReader.ReadToEnd();
myStreamReader.Close();
myResponseStream.Close();
return
retString;
}
命名空间System.Net,WebClient是一种更高级别的抽象,是HttpWebRequest为了简化最常见任务而创建的,使用过程中你会发现他缺少基本的header,timeoust的设置,不过这些可以通过继承httpwebrequest来实现。相对来说,WebClient比WebRequest更加简单,它相当于封装了request和response方法,不过需要说明的是,Webclient和WebRequest继承的是不同类,两者在继承上没有任何关系。使用WebClient可能比HttpWebRequest直接使用更慢(大约几毫秒),但却更为简单,减少了很多细节,代码量也比较少。
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public
class
WebClientHelper
{
public
static
string
DownloadString(
string
url)
{
WebClient wc =
new
WebClient();
//wc.BaseAddress = url; //设置根目录
wc.Encoding = Encoding.UTF8;
//设置按照何种编码访问,如果不加此行,获取到的字符串中文将是乱码
string
str = wc.DownloadString(url);
return
str;
}
public
static
string
DownloadStreamString(
string
url)
{
WebClient wc =
new
WebClient();
wc.Headers.Add(
"User-Agent"
,
"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36"
);
Stream objStream = wc.OpenRead(url);
StreamReader _read =
new
StreamReader(objStream, Encoding.UTF8);
//新建一个读取流,用指定的编码读取,此处是utf-8
string
str = _read.ReadToEnd();
objStream.Close();
_read.Close();
return
str;
}
public
static
void
DownloadFile(
string
url,
string
filename)
{
WebClient wc =
new
WebClient();
wc.DownloadFile(url, filename);
//下载文件
}
public
static
void
DownloadData(
string
url,
string
filename)
{
WebClient wc =
new
WebClient();
byte
[] bytes = wc.DownloadData(url);
//下载到字节数组
FileStream fs =
new
FileStream(filename, FileMode.Create);
fs.Write(bytes, 0, bytes.Length);
fs.Flush();
fs.Close();
}
public
static
void
DownloadFileAsync(
string
url,
string
filename)
{
WebClient wc =
new
WebClient();
wc.DownloadFileCompleted += DownCompletedEventHandler;
wc.DownloadFileAsync(
new
Uri(url), filename);
Console.WriteLine(
"下载中。。。"
);
}
private
static
void
DownCompletedEventHandler(
object
sender, AsyncCompletedEventArgs e)
{
Console.WriteLine(sender.ToString());
//触发事件的对象
Console.WriteLine(e.UserState);
Console.WriteLine(e.Cancelled);
Console.WriteLine(
"异步下载完成!"
);
}
public
static
void
DownloadFileAsync2(
string
url,
string
filename)
{
WebClient wc =
new
WebClient();
wc.DownloadFileCompleted += (sender, e) =>
{
Console.WriteLine(
"下载完成!"
);
Console.WriteLine(sender.ToString());
Console.WriteLine(e.UserState);
Console.WriteLine(e.Cancelled);
};
wc.DownloadFileAsync(
new
Uri(url), filename);
Console.WriteLine(
"下载中。。。"
);
}
}
HttpClient:
HttpClient是.NET4.5引入的一个HTTP客户端库,其命名空间为 System.Net.Http ,.NET 4.5之前我们可能使用WebClient和HttpWebRequest来达到相同目的。HttpClient利用了最新的面向任务模式,使得处理异步请求非常容易。它适合用于多次请求操作,一般设置好默认头部后,可以进行重复多次的请求,基本上用一个实例可以提交任何的HTTP请求。HttpClient有预热机制,第一次进行访问时比较慢,所以不应该用到HttpClient就new一个出来,应该使用单例或其他方式获取HttpClient的实例
单例模式:
单例模式(Singleton Pattern)这种类型的设计模式属于创建型模式,它提供了一种创建对象的最佳方式。
这种模式涉及到一个单一的类,该类负责创建自己的对象,同时确保只有单个对象被创建。这个类提供了一种访问其唯一的对象的方式,可以直接访问,不需要实例化该类的对象。
单例创建步骤:1、定义静态私有对象;2、定义私有构造函数;3、提供公共获取对象方法;
单例模式一般分为两种实现模式:懒汉模式、饿汉模式(以下为Java代码实现)
懒汉模式: 默认不会实例化,什么时候用什么时候new
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public
class
Singleton {
private
static
Singleton instance =
null
;
private
Singleton (){}
public
static
Singleton getInstance() {
if
(instance ==
null
) {
instance =
new
Singleton();
}
return
instance;
}
}
这种方式是最基本的实现方式,这种实现最大的问题就是不支持多线程。因为没有加锁 synchronized,所以严格意义上它并不算单例模式。
这种方式 lazy loading 很明显,不要求线程安全,在多线程不能正常工作。
饿汉模式: 类初始化时,会立即加载该对象,线程天生安全,调用效率高
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public
class
Singleton {
private
static
Singleton instance =
new
Singleton();
private
Singleton (){}
public
static
Singleton getInstance() {
return
instance;
}
}
双检锁/双重校验锁(DCL,即 double-checked locking):这种方式采用双锁机制,安全且在多线程情况下能保持高性能
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public
class
Singleton {
private
volatile
static
Singleton singleton;
private
Singleton (){}
public
static
Singleton getSingleton() {
if
(singleton ==
null
) {
synchronized (Singleton.
class
) {
if
(singleton ==
null
) {
singleton =
new
Singleton();
}
}
}
return
singleton;
}
}
HttpClient:
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public
class
HttpClientHelper
{
private
static
readonly
object
LockObj =
new
object
();
private
static
HttpClient client =
null
;
public
HttpClientHelper() {
GetInstance();
}
public
static
HttpClient GetInstance()
{
if
(client ==
null
)
{
lock
(LockObj)
{
if
(client ==
null
)
{
client =
new
HttpClient();
}
}
}
return
client;
}
public
async Task<
string
> PostAsync(
string
url,
string
strJson)
//post异步请求方法
{
try
{
HttpContent content =
new
StringContent(strJson);
content.Headers.ContentType =
new
System.Net.Http.Headers.MediaTypeHeaderValue(
"application/json"
);
//由HttpClient发出异步Post请求
HttpResponseMessage res = await client.PostAsync(url, content);
if
(res.StatusCode == System.Net.HttpStatusCode.OK)
{
string
str = res.Content.ReadAsStringAsync().Result;
return
str;
}
else
return
null
;
}
catch
(Exception ex)
{
return
null
;
}
}
public
string
Post(
string
url,
string
strJson)
//post同步请求方法
{
try
{
HttpContent content =
new
StringContent(strJson);
content.Headers.ContentType =
new
System.Net.Http.Headers.MediaTypeHeaderValue(
"application/json"
);
//client.DefaultRequestHeaders.Connection.Add("keep-alive");
//由HttpClient发出Post请求
Task<HttpResponseMessage> res = client.PostAsync(url, content);
if
(res.Result.StatusCode == System.Net.HttpStatusCode.OK)
{
string
str = res.Result.Content.ReadAsStringAsync().Result;
return
str;
}
else
return
null
;
}
catch
(Exception ex)
{
return
null
;
}
}
public
string
Get(
string
url)
{
try
{
var responseString = client.GetStringAsync(url);
return
responseString.Result;
}
catch
(Exception ex)
{
return
null
;
}
}
}
HttpClient有预热机制,第一次请求比较慢;可以通过初始化前发送一次head请求解决:
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_httpClient =
new
HttpClient() { BaseAddress =
new
Uri(BASE_ADDRESS) };
//帮HttpClient热身
_httpClient.SendAsync(
new
HttpRequestMessage {
Method =
new
HttpMethod(
"HEAD"
),
RequestUri =
new
Uri(BASE_ADDRESS +
"/"
) })
.Result.EnsureSuccessStatusCode();
三者区别列表:
C#中HttpWebRequest、WebClient、HttpClient的使用详解
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