C# Stream篇（五） -- MemoryStream

  public override void Write(byte[] buffer, int offset, int count) {
            if (!_isOpen) __Error.StreamIsClosed();
            if (!_writable) __Error.WriteNotSupported();
            if (buffer==null)
                throw new ArgumentNullException("buffer", Environment.GetResourceString("ArgumentNull_Buffer"));
            if (offset  _length) {
                bool mustZero = _position > _length;
                if (i > _capacity) {
                    bool allocatedNewArray = EnsureCapacity(i);
                    if (allocatedNewArray)
                        mustZero = false;
                }
                if (mustZero)
                    Array.Clear(_buffer, _length, i - _length);
                _length = i;
            }
            if (count = 0)
                    _buffer[_position + byteCount] = buffer[offset + byteCount];
            }
            else
                Buffer.InternalBlockCopy(buffer, offset, _buffer, _position, count);
            _position = i;
            return;
        }

         //测试byte数组 假设该数组容量是256M
            byte[] testBytes=new byte[256*1024*1024];
            MemoryStream ms = new MemoryStream();
            using (ms)
            {
                for (int i = 0; i 
 

        /// 

        /// 演示在xmlWriter中使用MemoryStream
        /// 
        public static void UseMemoryStreamInXMLWriter()
        {
            MemoryStream ms = new MemoryStream();
            using (ms)
            {
                //定义一个XMLWriter
                using (XmlWriter writer = XmlWriter.Create(ms))
                {
                    //写入xml头
                    writer.WriteStartDocument(true);
                    //写入一个元素
                    writer.WriteStartElement("Content");
                    //为这个元素新增一个test属性
                    writer.WriteStartAttribute("test");
                    //设置test属性的值
                    writer.WriteValue("逆时针的风");
                    //释放缓冲，这里可以不用释放，但是在实际项目中可能要考虑部分释放对性能带来的提升
                    writer.Flush();
                    Console.WriteLine("此时内存使用量为:{2}KB,该MemoryStream的已经使用的容量为{0}byte,默认容量为{1}byte",
                        Math.Round((double)ms.Length, 4), ms.Capacity,GC.GetTotalMemory(false)/1024);
                    Console.WriteLine("重新定位前MemoryStream所在的位置是{0}",ms.Position);
                    //将流中所在的当前位置往后移动7位，相当于空格
                    ms.Seek(7, SeekOrigin.Current);
                    Console.WriteLine("重新定位后MemoryStream所在的位置是{0}", ms.Position);
                    //如果将流所在的位置设置为如下所示的位置则xml文件会被打乱
                    //ms.Position = 0;
                    writer.WriteStartElement("Content2");
                    writer.WriteStartAttribute("testInner");
                    writer.WriteValue("逆时针的风Inner");
                    writer.WriteEndElement();
                    writer.WriteEndElement();
                    //再次释放
                    writer.Flush();
                    Console.WriteLine("此时内存使用量为:{2}KB,该MemoryStream的已经使用的容量为{0}byte,默认容量为{1}byte",
                        Math.Round((double)ms.Length, 4), ms.Capacity, GC.GetTotalMemory(false)/1024);
                    //建立一个FileStream  文件创建目的地是d:\test.xml
                    FileStream fs = new FileStream(@"d:\test.xml",FileMode.OpenOrCreate);
                    using (fs)
                    {
                        //将内存流注入FileStream
                        ms.WriteTo(fs);
                        if(ms.CanWrite)
                          //释放缓冲区
                        fs.Flush();
                    }
                }
            }
        }

  public class ImageHandler : IHttpHandler
    {
        #region IHttpHandler Members

        public bool IsReusable
        {
            get { return true; }
        }

        /// 

        /// 实现IHTTPHandler后必须实现的方法
        /// 
        /// HttpContext上下文
        public void ProcessRequest(HttpContext context)
        {
            context.Response.Clear();
            //得到图片名
            var imageName = context.Request["ImageName"] == null ? "逆时针的风"
                : context.Request["ImageName"].ToString();
            //得到图片ID,这里只是演示，实际项目中不是这么做的
            var id = context.Request["Id"] == null ? "01"
                : context.Request["Id"].ToString();
            //得到图片地址
            var stringFilePath = context.Server.MapPath(string.Format("~/Image/{0}{1}.jpg", imageName, id));
            //声明一个FileStream用来将图片暂时放入流中
            FileStream stream = new FileStream(stringFilePath, FileMode.Open);
            using (stream)
            {
                //透过GetImageFromStream方法将图片放入byte数组中
                byte[] imageBytes = this.GetImageFromStream(stream,context);
                //上下文确定写到客户短时的文件类型
                context.Response.ContentType = "image/jpeg";
                //上下文将imageBytes中的数据写到前段
                context.Response.BinaryWrite(imageBytes);
                stream.Close();
            }
        }

        /// 

        /// 将流中的图片信息放入byte数组后返回该数组
        /// 
        /// 文件流
        /// 上下文
        /// 
        private byte[] GetImageFromStream(FileStream stream, HttpContext context)
        {
            //通过stream得到Image
            Image image = Image.FromStream(stream);
            //加上水印
            image = SetWaterImage(image, context);
            //得到一个ms对象
            MemoryStream ms = new MemoryStream();
            using (ms)
            {
               //将图片保存至内存流
                image.Save(ms, ImageFormat.Jpeg);
                byte[] imageBytes = new byte[ms.Length];
                ms.Position = 0;
                //通过内存流读取到imageBytes
                ms.Read(imageBytes, 0, imageBytes.Length);
                ms.Close();
                //返回imageBytes
                return imageBytes;
            }
        }
        /// 

        /// 为图片加上水印，这个方法不用在意，只是演示，所以没加透明度
        /// 下次再加上吧
        /// 
        /// 需要加水印的图片
        /// 上下文
        /// 
        private Image SetWaterImage(Image image,HttpContext context) 
        {
            Graphics graphics = Graphics.FromImage(image);
            Image waterImage = Image.FromFile(context.Server.MapPath("~/Image/逆时针的风01.jpg"));
            //在大图右下角画上水印图就行
            graphics.DrawImage(waterImage,
                new Point { 
                    X = image.Size.Width - waterImage.Size.Width,
                    Y = image.Size.Height - waterImage.Size.Height 
                });
            return image;
        }

        #endregion
    }

    

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