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HomeBackend DevelopmentPHP TutorialJSP技巧:发送动态图像_PHP

页面(或者servlet)中发送动态产生的图像?这篇技巧告诉你如何做。要运行这里的代码,你需要一个Tomcat或者其他支持JSP 1.1的web服务器。

  当一个web页面带有image/jpeg (或者其他的图像格式)的MIME类型被发送时,你的浏览器将那个返回结果当作一个图像,然后浏览器显示图像,作为页面的一部分或者完全作为图像自身。要为你的jsp页面设置MIME类型,你需要设置页面的contentType属性:
  

  然后你需要创建一个BufferedImage绘制你的动态图像:
  BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

  创建完一个BufferedImage后,你需要得到图形环境进行绘制,一个Graphics或者Graphics2D对象:

  Graphics g = image.getGraphics();
  // or
  Graphics2d g2d = image.createGraphics();

   从现在起你就可以绘制图像内容了。对图形环境绘制就会画到BufferedImage。最开始这个图像都是黑色的,因此用你希望的背景颜色填充图像是一个不错的主意,然后,当你完成图像的绘制,你需要dispose图形环境:

  g.dispose();
  // or
  g2d.dispose();


 一旦完成图像的绘制,你在response中返回那个图像。你可以使用非标准的com.sun.image.codec.jpeg包中的JPEGImageEncoder类编码图像,或者如果你使用JDK1.4,你可以使用标准的ImageIO类。在使用JPEGImageEncoder时有一个技巧,你必须从ServletResponse取来ServletOutputStream而不能使用隐含的JSP输出变量out。

  ServletOutputStream sos = response.getOutputStream();
  JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(sos);
  encoder.encode(image);
  // or
  ImageIO.write(image, "JPEG", out);

  这里有一个从所有的可能方案中(例如g.dispose();或者g2d.dispose();)选取的一个完整的范例.这个例子使用Graphics对象绘制一个随机的多边形,图像通过JPEGImageEncoder绘制,你可以自由设置多边形的顶点数得到更复杂的形状,换言之,有更多顶点和边。

  要运行这个范例,将从""之间的jsp代码放到一个名为image.jsp的文件中,将那个文件放到你的web服务器可以找到的地方,在使用Tomcat的情况下是ROOT目录,启动Tomcat,访问http://localhost:8080/image.jsp
   import="java.awt.*,java.awt.image.*,
  com.sun.image.codec.jpeg.*,java.util.*"
  %>  
    // Create image
  int width=200, height=200;
  BufferedImage image = new BufferedImage(width,
  height, BufferedImage.TYPE_INT_RGB);
  // Get drawing context  (代码实验室)
  Graphics g = image.getGraphics();
  // Fill background
  g.setColor(Color.white);
  g.fillRect(0, 0, width, height);
  // Create random polygon
  Polygon poly = new Polygon();
  Random random = new Random();
  for (int i=0; i < 5; i++) {
  poly.addPoint(random.nextInt(width),
  random.nextInt(height));
  }
  // Fill polygon
  g.setColor(Color.cyan);
  g.fillPolygon(poly);
  // Dispose context
  g.dispose();
  // Send back image
  ServletOutputStream sos = response.getOutputStream();
  JPEGImageEncoder encoder =
  JPEGCodec.createJPEGEncoder(sos);
  encoder.encode(image);
  %> (代码实验室)

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