Java获取系统文件类型图标并显示在JSP上

在网站制作中通常需要上传附件，而对于附件我们往往希望在其名称前面有类似于Windows系统中的类型图标，那么怎么根据附件的类型来显示不同的图标呢？目前有两种解决方案：
第一种：将所有类型文件的图标图片放置到项目中，然后通过分析文件的扩展名来调用相应的图片，这种方式比较简单常见，但是我们往往无法弄到所有文件类型的图标，而且也不能排除意外情况的出现，这里就不在介绍了；
第二种：通过java调用系统的文件类型图标然后显示出来，好处是可以显示跟操作系统中一模一样的图标，但是要复杂一些，下面详细介绍。
1、JSP

<img src="fileAction!dispalyIcon?dirName=<%=request.getAttribute("fileName").toString()%>" style="width:16px;height:16px;"/>

2、fileAction

@Component("fileAction")
public class FileAction extends ActionSupport { 
private String dirName;
public String getDirName() {
		return dirName;
	}

	public void setDirName(String dirName) {
		this.dirName = dirName;
	}
public void dispalyIcon() {
		HttpServletResponse response = ServletActionContext.getResponse();
		response.setContentType("image/png");
		try {
			OutputStream sos = response.getOutputStream();
			BufferedImage myImage = CommonTool.getImageByFileTyle(dirName);
			ImageIO.write(myImage, "png", sos);
			sos.flush();
			sos.close();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
}

3、CommonTool

public class CommonTool {
	public static BufferedImage getImageByFileTyle(String filename)
			throws FileNotFoundException {
		File file = null;
		String extension = filename.substring(filename.lastIndexOf("."))
				.toLowerCase();
		try {
			file = File.createTempFile("icon", extension);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return toBufferedImage(toImage(toIcon(file)));

	}

	public static Icon toIcon(File file) throws FileNotFoundException {
		ShellFolder shellFolder = ShellFolder.getShellFolder(file);
		Icon icon = new ImageIcon(shellFolder.getIcon(true));
		return icon;
	}

	public static Image toImage(Icon icon) {
		if (icon instanceof ImageIcon) {
			return ((ImageIcon) icon).getImage();
		} else {
			int w = icon.getIconWidth();
			int h = icon.getIconHeight();
			GraphicsEnvironment ge = GraphicsEnvironment
					.getLocalGraphicsEnvironment();
			GraphicsDevice gd = ge.getDefaultScreenDevice();
			GraphicsConfiguration gc = gd.getDefaultConfiguration();
			BufferedImage image = gc.createCompatibleImage(w, h);
			Graphics2D g = image.createGraphics();
			icon.paintIcon(null, g, 0, 0);
			g.dispose();
			return image;
		}
	}

	private static boolean hasAlpha(Image image) {
		// If buffered image, the color model is readily available
		if (image instanceof BufferedImage) {
			BufferedImage bimage = (BufferedImage) image;
			return bimage.getColorModel().hasAlpha();
		}

		// Use a pixel grabber to retrieve the image's color model;
		// grabbing a single pixel is usually sufficient
		PixelGrabber pg = new PixelGrabber(image, 0, 0, 1, 1, false);
		try {
			pg.grabPixels();
		} catch (InterruptedException e) {
		}

		// Get the image's color model
		ColorModel cm = pg.getColorModel();
		return cm.hasAlpha();
	}

	// This method returns a buffered image with the contents of an image
	public static BufferedImage toBufferedImage(Image image) {
		if (image instanceof BufferedImage) {
			return (BufferedImage) image;
		}

		// This code ensures that all the pixels in the image are loaded
		image = new ImageIcon(image).getImage();

		// Determine if the image has transparent pixels; for this method's
		// implementation, see Determining If an Image Has Transparent Pixels
		boolean hasAlpha = hasAlpha(image);

		// Create a buffered image with a format that's compatible with the
		// screen
		BufferedImage bimage = null;
		GraphicsEnvironment ge = GraphicsEnvironment
				.getLocalGraphicsEnvironment();
		try {
			// Determine the type of transparency of the new buffered image
			int transparency = Transparency.OPAQUE;
			if (hasAlpha) {
				transparency = Transparency.BITMASK;
			}

			// Create the buffered image
			GraphicsDevice gs = ge.getDefaultScreenDevice();
			GraphicsConfiguration gc = gs.getDefaultConfiguration();
			bimage = gc.createCompatibleImage(image.getWidth(null), image
					.getHeight(null), transparency);
		} catch (HeadlessException e) {
			// The system does not have a screen
		}

		if (bimage == null) {
			// Create a buffered image using the default color model
			int type = BufferedImage.TYPE_INT_RGB;
			if (hasAlpha) {
				type = BufferedImage.TYPE_INT_ARGB;
			}
			bimage = new BufferedImage(image.getWidth(null), image
					.getHeight(null), type);
		}

		// Copy image to buffered image
		Graphics g = bimage.createGraphics();

		// Paint the image onto the buffered image
		g.drawImage(image, 0, 0, null);
		g.dispose();

		return bimage;
	}
}

4、struts.xml

<action name="fileAction" class="com.render.action.cyl.FileAction">
	<result name="input">login.jsp</result>
</action>