using System.IO;

namespace URLRewriter
{
    /// <summary>
    /// 生成htm静态页面
    /// </summary>
    public class ResponseFilter : Stream
    {
        private Stream m_sink;
        private long m_position;
        private FileStream fs;

        public ResponseFilter(Stream sink, string filePath)
        {
            m_sink = sink;
            fs = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.Write);
        }

        // The following members of Stream must be overriden.
        public override bool CanRead
        { get { return true; } }

        public override bool CanSeek
        { get { return false; } }

        public override bool CanWrite
        { get { return false; } }

        public override long Length
        { get { return 0; } }

        public override long Position
        {
            get { return m_position; }
            set { m_position = value; }
        }

        public override long Seek(long offset, System.IO.SeekOrigin direction)
        {
            return 0;
        }

        public override void SetLength(long length)
        {
            m_sink.SetLength(length);
        }

        public override void Close()
        {
            m_sink.Close();
            fs.Close();
        }

        public override void Flush()
        {
            m_sink.Flush();
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            return m_sink.Read(buffer, offset, count);
        }

        // Override the Write method to filter Response to a file.
        public override void Write(byte[] buffer, int offset, int count)
        {
            //Write out the response to the browser.
            m_sink.Write(buffer, 0, count);

            //Write out the response to the file.
            fs.Write(buffer, 0, count);
        }
    }
}

上边的这个类在生成静态页的时候，如果.net解析代码时，遇到错误，它依然会生成一个静态页面，而且这个静态页面在程序运行结束的时候，还处于打开状态。

显然这是我们不愿意看到的，而且这个类还不支持并发操作，如果和某一页面的关联的静态页失效了，假定这时候有两个用户同时访问这个页面,其中一个用户正在向静态页面写入数据，另外一个用户却需要访问这个已被别人打开的页面，系统同样会出现错误。基于这两个问题，我把这个类修改成下边的样子，就可以解决上述问题了。

using System.IO;
using System.Web;

namespace URLRewriter
{
    /// <summary>
    /// 生成htm静态页面
    /// </summary>
    public class ResponseFilter : Stream
    {
        private Stream m_sink;
        private long m_position;
        private FileStream fs;
        private string filePath = string.Empty;

        public ResponseFilter(Stream sink, string filePath)
        {
            this.m_sink = sink;
            this.filePath = filePath;
        }

        // The following members of Stream must be overriden.
        public override bool CanRead
        { get { return true; } }

        public override bool CanSeek
        { get { return false; } }

        public override bool CanWrite
        { get { return false; } }

        public override long Length
        { get { return 0; } }

        public override long Position
        {
            get { return m_position; }
            set { m_position = value; }
        }

        public override long Seek(long offset, System.IO.SeekOrigin direction)
        {
            return 0;
        }

        public override void SetLength(long length)
        {
            this.m_sink.SetLength(length);
        }

        public override void Close()
        {
            this.m_sink.Close();
            this.fs.Close();
        }

        public override void Flush()
        {
            this.m_sink.Flush();
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            return m_sink.Read(buffer, offset, count);
        }

        // Override the Write method to filter Response to a file.
        public override void Write(byte[] buffer, int offset, int count)
        {
            //首先判断有没有系统错误
            if (HttpContext.Current.Error == null)
            {
                try
                {
                    if (fs == null)
                        this.fs = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.Write);
                    //将数据写入静态文件.
                    this.fs.Write(buffer, 0, count);
                }
                catch
                {
                    if (fs != null)
                    {
                        //关闭流
                        this.fs.Close();
                        //删除静态页面
                        if (File.Exists(filePath))
                        {
                            File.Delete(filePath);
                            return;
                        }
                    }
                }
            }
            //Write out the response to the browser.
            this.m_sink.Write(buffer, 0, count);
        }
    }
}

protected override void OnInit(EventArgs e)
{
    if (!this.IsPostBack)
    {
        string filePath = this.Server.MapPath(Common.AppName) + "\\index.htm";
        Response.Filter = new AspNetFilter(Response.Filter, filePath);
    }
    base.OnInit(e);
}