一、 简介
作为ASP.NET基本对象之一的Response对象不但可以通过Write()方法直接在页面上输出字符串数据,而且还可以使用BinaryWrite()方法直接显示二进制表示的数据,如图像、图片等。
本文示例小工程将向你展示如何使用Response对象在ASP.NET 2.0 Web页面中输出直接存储在SQL Server 2005数据库中的图像数据。
【注意】在本例中,我们没有讨论仅在SQL Server 2005表格中存储图像的URL的情形。因为这种情形是实际开发中被广为采用的方法,所以,读者不难在Web上搜到相应的使用案例。
首先,让我们来分析一个简单的直接在Web页面上绘制并输出图像数据的例子。
作为ASP.NET基本对象之一的Response对象不但可以通过Write()方法直接在页面上输出字符串数据,而且还可以使用BinaryWrite()方法直接显示二进制表示的数据,如图像、图片等。
本文示例小工程将向你展示如何使用Response对象在ASP.NET 2.0 Web页面中输出直接存储在SQL Server 2005数据库中的图像数据。
【注意】在本例中,我们没有讨论仅在SQL Server 2005表格中存储图像的URL的情形。因为这种情形是实际开发中被广为采用的方法,所以,读者不难在Web上搜到相应的使用案例。
首先,让我们来分析一个简单的直接在Web页面上绘制并输出图像数据的例子。
二、 直接在Web页面上绘制并输出图像数据
下面的代码示例在请求页面时将绘制三个部分重叠的矩形。该代码首先将ContentType属性设置为image/jpeg,以便将整个页面呈现为一幅JPEG图像。第二步,该代码调用Clear方法以确保不会将无关的内容(包括标头)与此响应一同发送。第三步,该代码将BufferOutput属性设置为true,从而使该页面在完全处理之后再发送到发出请求的客户端。第四步,创建两个用于绘制矩形的对象,即Bitmap和Graphics对象。在该页中创建的变量将作为绘制矩形的坐标和在最大的矩形中显示的字符串。
在绘制三个矩形和其中显示的字符串时,将Bitmap保存到与OutputStream属性相关联的Stream对象中,并将其格式设置为JPEG。接下来,该代码调用Dispose和Dispose方法来释放资源—这些资源为两个绘制对象所使用。最后,该代码调用Flush方法将缓冲的响应发送到请求客户端。
完整的实现代码如下所示:
下面的代码示例在请求页面时将绘制三个部分重叠的矩形。该代码首先将ContentType属性设置为image/jpeg,以便将整个页面呈现为一幅JPEG图像。第二步,该代码调用Clear方法以确保不会将无关的内容(包括标头)与此响应一同发送。第三步,该代码将BufferOutput属性设置为true,从而使该页面在完全处理之后再发送到发出请求的客户端。第四步,创建两个用于绘制矩形的对象,即Bitmap和Graphics对象。在该页中创建的变量将作为绘制矩形的坐标和在最大的矩形中显示的字符串。
在绘制三个矩形和其中显示的字符串时,将Bitmap保存到与OutputStream属性相关联的Stream对象中,并将其格式设置为JPEG。接下来,该代码调用Dispose和Dispose方法来释放资源—这些资源为两个绘制对象所使用。最后,该代码调用Flush方法将缓冲的响应发送到请求客户端。
完整的实现代码如下所示:
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接下来,让我们讨论本文重点—如何在ASP页面中输出直接存储在数据库中的图像数据。
三、 事件设计
示例工程中的DispImage.aspx页面在其初始化函数Page_Load(object sender,EventArgs e)中使用Response对象输出一幅图像—该图像存储在SQL Server 2005 Express Edition数据库中,并用二进制表示。
在代码中,我们首先从数据库PictureDB的表格PictureTab中获取一个ID值为1的图片,然后使用byte数组Data保存图片的数据。然后,我们可以基于如下步骤来输出相应的图像:
1. 设置Response对象的输出类型;
2. 输出图像的文件头;
3. 输出图像的二进制数据;
4. 结束输出。如果图片太大,还可以使用输出缓冲的方法。
函数Page_Load(object sender,EventArgs e)的程序代码如下:
示例工程中的DispImage.aspx页面在其初始化函数Page_Load(object sender,EventArgs e)中使用Response对象输出一幅图像—该图像存储在SQL Server 2005 Express Edition数据库中,并用二进制表示。
在代码中,我们首先从数据库PictureDB的表格PictureTab中获取一个ID值为1的图片,然后使用byte数组Data保存图片的数据。然后,我们可以基于如下步骤来输出相应的图像:
1. 设置Response对象的输出类型;
2. 输出图像的文件头;
3. 输出图像的二进制数据;
4. 结束输出。如果图片太大,还可以使用输出缓冲的方法。
函数Page_Load(object sender,EventArgs e)的程序代码如下:
1
protected
void
Page_Load(
object
sender,EventArgs e)
2
{ ///创建链接 3
SqlConnection myConnection = new SqlConnection( 4
ConfigurationManager.ConnectionStrings["SQLCONNECTIONSTRING"].ConnectionString); 5
///定义SQL语句 6
string cmdText = "SELECT * FROM PictureTab WHERE PictureID='1'"; 7
///创建Command 8
SqlCommand myCommand = new SqlCommand(cmdText,myConnection); 9
///定义DataReader 10
SqlDataReader dr = null; 11
try 12
{ ///打开链接 13
myConnection.Open(); 14
///读取数据 15
dr = myCommand.ExecuteReader(CommandBehavior.CloseConnection); 16
} 17
catch(SqlException ex) 18
{ ///抛出异常 19
throw new Exception(ex.Message,ex); 20
} 21
///定义保存数据的字节数组 22
byte[] Data = null; 23
while(dr.Read()) 24
{ ///读取数据 25
Data = (byte[])dr["Data"]; 26
Response.ContentType = dr["Type"].ToString(); 27
} 28
dr.Close(); 29
//显示图片数据 30
this.EnableViewState = false; 31
///输出文件头 32
Response.AppendHeader("Content-Length",Data.Length.ToString()); 33
///输出文件的数据 34
Response.BinaryWrite(Data); 35
///结束输出 36
Response.End(); 37
}
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本文转自朱先忠老师51CTO博客,原文链接:
http://blog.51cto.com/zhuxianzhong/59360
,如需转载请自行联系原作者