ShowImageFromDiskServlet.java代码如下：

import java.io.*;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class ShowImageFromDiskServlet extends HttpServlet {

    private static final long serialVersionUID = -3099500650220853030L;
    private static final Log log = LogFactory.getLog(ShowImageFromDiskServlet.class);

    String imagePath;

    public ShowImageFromDiskServlet() {
    }

    @Override
    public void init(ServletConfig config) {
        imagePath = config.getInitParameter("imagePath");
        log.info("图片路径：" + imagePath);
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(response.getOutputStream());

        File file = new File(imagePath);

        BufferedInputStream bufferedInputStream = new BufferedInputStream(new FileInputStream(file));

        byte[] buffer = new byte[1024];

        for (int len; (len = bufferedInputStream.read(buffer)) > 0; ) {
            bufferedOutputStream.write(buffer, 0, len);
        }

        // bufferedOutputStream.flush();//关闭时会自动刷新，无需显示调用，否则必须显示调用
        bufferedOutputStream.close();
        bufferedInputStream.close();
    }

    @Deprecated
	protected byte[] readStream(InputStream in) {
		ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
		int data;
		try {
			while ((data = in.read()) != -1) {
				outputStream.write(data);
			}
			return outputStream.toByteArray();
		} catch (IOException e) {
			e.printStackTrace();
			return null;
		}
	}
}

spring mvc 通过字节流返回图像

    /**
     * 通过url请求返回图像的字节流
     */
    @RequestMapping("/icon/{cateogry}")
    public void getIcon(@PathVariable("cateogry") String cateogry,
                        HttpServletRequest request,
                        HttpServletResponse response) throws IOException {

        if (StringUtils.isEmpty(cateogry)) {
            cateogry = "";
        }

        String fileName = request.getSession().getServletContext().getRealPath("/") + "resource/icons/auth/" + cateogry.toUpperCase().trim() + ".png";

        File file = new File(fileName);

        // 判断文件是否存在如果不存在就返回默认图标
        if (!(file.exists() && file.canRead())) {
            file = new File(request.getSession().getServletContext().getRealPath("/") + "resource/icons/auth/root.png");
        }

        FileInputStream inputStream = new FileInputStream(file);
        byte[] data = new byte[(int) file.length()];
        int length = inputStream.read(data);
        inputStream.close();

        response.setContentType("image/png");

        OutputStream stream = response.getOutputStream();
        stream.write(data);
        stream.flush();
        stream.close();
    }

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http://www.dookay.com/zh-cn/n/929