《C# 爬虫 破境之道》：第一境 爬虫原理 — 第三节：WebResponse

第二节中，我们介绍了WebRequest，它可以帮助我们发送一个请求，不过正所谓“来而不往非礼也”，对方收到我们的请求，不给点回复，貌似不太合适（不过，还真有脸皮厚的：P）。

接下来，就重点研究一下，我们收到的回复，是个什么样的东东

[Code 1.3.1]

     //
     // Summary:
     //     Provides a response from a Uniform Resource Identifier (URI). This is an abstract
     //     class.
     public abstract class WebResponse : MarshalByRefObject, ISerializable, IDisposable
     {
         //
         // Summary:
         //     Initializes a new instance of the System.Net.WebResponse class.
         protected WebResponse();
         //
         // Summary:
         //     Initializes a new instance of the System.Net.WebResponse class from the specified
         //     instances of the System.Runtime.Serialization.SerializationInfo and System.Runtime.Serialization.StreamingContext
         //     classes.
         //
         // Parameters:
         //   serializationInfo:
         //     An instance of the System.Runtime.Serialization.SerializationInfo class that
         //     contains the information required to serialize the new System.Net.WebRequest
         //     instance.
         //
         //   streamingContext:
         //     An instance of the System.Runtime.Serialization.StreamingContext class that indicates
         //     the source of the serialized stream that is associated with the new System.Net.WebRequest
         //     instance.
         //
         // Exceptions:
         //   T:System.NotSupportedException:
         //     Any attempt is made to access the constructor, when the constructor is not overridden
         //     in a descendant class.
         protected WebResponse(SerializationInfo serializationInfo, StreamingContext streamingContext);
 
         //
         // Summary:
         //     Gets a System.Boolean value that indicates whether this response was obtained
         //     from the cache.
         //
         // Returns:
         //     true if the response was taken from the cache; otherwise, false.
         public virtual bool IsFromCache { get; }
         //
         // Summary:
         //     Gets a System.Boolean value that indicates whether mutual authentication occurred.
         //
         // Returns:
         //     true if both client and server were authenticated; otherwise, false.
         public virtual bool IsMutuallyAuthenticated { get; }
         //
         // Summary:
         //     When overridden in a descendant class, gets or sets the content length of data
         //     being received.
         //
         // Returns:
         //     The number of bytes returned from the Internet resource.
         //
         // Exceptions:
         //   T:System.NotSupportedException:
         //     Any attempt is made to get or set the property, when the property is not overridden
         //     in a descendant class.
         public virtual long ContentLength { get; set; }
         //
         // Summary:
         //     When overridden in a derived class, gets or sets the content type of the data
         //     being received.
         //
         // Returns:
         //     A string that contains the content type of the response.
         //
         // Exceptions:
         //   T:System.NotSupportedException:
         //     Any attempt is made to get or set the property, when the property is not overridden
         //     in a descendant class.
         public virtual string ContentType { get; set; }
         //
         // Summary:
         //     When overridden in a derived class, gets the URI of the Internet resource that
         //     actually responded to the request.
         //
         // Returns:
         //     An instance of the System.Uri class that contains the URI of the Internet resource
         //     that actually responded to the request.
         //
         // Exceptions:
         //   T:System.NotSupportedException:
         //     Any attempt is made to get or set the property, when the property is not overridden
         //     in a descendant class.
         public virtual Uri ResponseUri { get; }
         //
         // Summary:
         //     When overridden in a derived class, gets a collection of header name-value pairs
         //     associated with this request.
         //
         // Returns:
         //     An instance of the System.Net.WebHeaderCollection class that contains header
         //     values associated with this response.
         //
         // Exceptions:
         //   T:System.NotSupportedException:
         //     Any attempt is made to get or set the property, when the property is not overridden
         //     in a descendant class.
         public virtual WebHeaderCollection Headers { get; }
         //
         // Summary:
         //     Gets a value that indicates if headers are supported.
         //
         // Returns:
         //     Returns System.Boolean. true if headers are supported; otherwise, false.
         public virtual bool SupportsHeaders { get; }
 
         //
         // Summary:
         //     When overridden by a descendant class, closes the response stream.
         //
         // Exceptions:
         //   T:System.NotSupportedException:
         //     Any attempt is made to access the method, when the method is not overridden in
         //     a descendant class.
         public virtual void Close();
         //
         // Summary:
         //     Releases the unmanaged resources used by the System.Net.WebResponse object.
         public void Dispose();
         //
         // Summary:
         //     When overridden in a descendant class, returns the data stream from the Internet
         //     resource.
         //
         // Returns:
         //     An instance of the System.IO.Stream class for reading data from the Internet
         //     resource.
         //
         // Exceptions:
         //   T:System.NotSupportedException:
         //     Any attempt is made to access the method, when the method is not overridden in
         //     a descendant class.
         public virtual Stream GetResponseStream();
         //
         // Summary:
         //     Releases the unmanaged resources used by the System.Net.WebResponse object, and
         //     optionally disposes of the managed resources.
         //
         // Parameters:
         //   disposing:
         //     true to release both managed and unmanaged resources; false to releases only
         //     unmanaged resources.
         protected virtual void Dispose(bool disposing);
         //
         // Summary:
         //     Populates a System.Runtime.Serialization.SerializationInfo with the data that
         //     is needed to serialize the target object.
         //
         // Parameters:
         //   serializationInfo:
         //     The System.Runtime.Serialization.SerializationInfo to populate with data.
         //
         //   streamingContext:
         //     A System.Runtime.Serialization.StreamingContext that specifies the destination
         //     for this serialization.
         protected virtual void GetObjectData(SerializationInfo serializationInfo, StreamingContext streamingContext);
     }

System.Net.WebResponse 全貌

相比较WebRequest而言，WebResponse简单许多，这里就不再分解片断讲解了。有事儿说事儿，不要以貌取人：D

首先，与WebRequest的类似，它还是抽象类，两个构造函数的结构，一票子虚属性，大部分都是只读的，和一票子虚方法。

其次，与WebRequest不同，它继承了System.IDisposable接口，提醒我们啊，用完了，要释放啊~~~~~~

几个属性

[Code 1.3.2]

         /// <summary>
         /// 只读，指示这个回复是不是从缓存中获取的
         /// </summary>
         public virtual bool IsFromCache { get; }
         /// <summary>
         /// 只读，指示是否发生相互认证
         /// </summary>
         public virtual bool IsMutuallyAuthenticated { get; }
         /// <summary>
         /// 指示收到的数据长度
         /// </summary>
         public virtual long ContentLength { get; set; }
         /// <summary>
         /// 指示收到的内容类型
         /// </summary>
         public virtual string ContentType { get; set; }
         /// <summary>
         /// 只读，指示收到的实际资源URI
         /// </summary>
         public virtual Uri ResponseUri { get; }
         /// <summary>
         /// 只读，Header集合，HTTP协议中的重点
         /// </summary>
         public virtual WebHeaderCollection Headers { get; }
         /// <summary>
         /// 只读，指示是否支持Header集合
         /// </summary>
         public virtual bool SupportsHeaders { get; }

System.Net.WebResponse 属性

重要的属性有Headers、ContentType、ContentLength。对于分析数据都是举足轻重的。

几个方法

[Code 1.3.3]

         /// <summary>
         /// 获得目标资源的数据流
         /// </summary>
         public virtual Stream GetResponseStream();
         /// <summary>
         /// 关闭Response流
         /// </summary>
         public virtual void Close();
         /// <summary>
         /// 释放WebResponse对象
         /// </summary>
         public void Dispose();
         /// <summary>
         /// 释放WebResponse对象
         /// </summary>
         protected virtual void Dispose(bool disposing);
         /// <summary>
         /// 使用序列化目标对象所需的数据填充System.Runtime.Serialization.SerializationInfo
         /// </summary>
         protected virtual void GetObjectData(SerializationInfo serializationInfo, StreamingContext streamingContext);

System.Net.WebResponse 方法

重要的方法有GetResponseStream、Close。对于获取数据至关重要。

总而言之，WebResponse还是比较简单的，给我们留下的坑不多。与WebRequest的讲解一样，干嚼无味，还是在实例中体会个中滋味吧：P

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