HttpServletResponse 如何将图片下载到客户端(OutputStream，PrintWriter)呢？

在HttpServletResponse图片下载中，笔者建议使用OutputStream流
由于OutputStream流是一个字节流，可以处理任何类ing的数据

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  
	 //1、得到文件的绝对路径,并且通过该路径得到一个字节输入流  
	 String path = this.getServletContext().getRealPath("/WEB-INF/classes/java265img.png");//得到下载文件的绝对路径  
	 FileInputStream fis = new FileInputStream(path);  
	 //2、创建字节输出流  
	 ServletOutputStream sos = resp.getOutputStream();  
	 //3、得到下载的文件名  
	 String filename = path.substring(path.lastIndexOf("\\")+1);//得到的文件名为TomCat.png  
	 //4、设置文件编码  
	 filename = URLEncoder.encode(filename, "UTF-8");//编码为UTF-8  
	 //5、告知客户端(浏览器)要下载文件  
	 resp.setHeader("content-disposition", "attachment;filename="+filename);  
	 resp.setHeader("content-type", "image/png");//文件类型  
	 //6、输出  
	 byte[] b = new byte[1024];  
	 int len = 0;  
	 while((len=fis.read(b)) != -1){  
		sos.write(b, 0, len);  
	 }  
	 sos.close();  
	 fis.close();  
}  

PrintWriter下载图片

//HttpServletResponse PrintWriter下载图片实例
private void downloadFileByPrintWriter(HttpServletResponse response) throws FileNotFoundException, IOException {
    String realPath = this.getServletContext().getRealPath("/download/java265img.JPG");//获取要下载的文件的绝对路径
    String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);//获取要下载的文件名
    //设置content-disposition响应头控制浏览器以下载的形式打开文件，中文文件名要使用URLEncoder.encode方法进行编码
    response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(fileName, "UTF-8"));
    FileReader in = new FileReader(realPath);
    int len = 0;
    char[] buffer = new char[1024];
    PrintWriter out = response.getWriter();
    while ((len = in.read(buffer)) > 0) {
        out.write(buffer,0,len);//将缓冲区的数据输出到客户端浏览器
    }
    in.close();
}