《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);
    }

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; }

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);

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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