response实现文件的下载

@Controller  
public class FileController implements ServletContextAware{   
    //Spring这里是通过实现ServletContextAware接口来注入ServletContext对象   
    private ServletContext servletContext;   
  
  
    @RequestMapping("file/download")   
    public void fileDownload(HttpServletResponse response){   
        //获取网站部署路径(通过ServletContext对象)，用于确定下载文件位置，从而实现下载   
        String path = servletContext.getRealPath("/");   
  　　　　response.rset();         //清楚空格等操作
        //1.设置文件ContentType类型，这样设置，会自动判断下载文件类型   
        response.setContentType("multipart/form-data");   
        //2.设置文件头：最后一个参数是设置下载文件名(假如我们叫a.pdf)   
        response.setHeader("Content-Disposition", "attachment;fileName="+"a.pdf");   
        ServletOutputStream out;   
        //通过文件路径获得File对象(假如此路径中有一个download.pdf文件)   
        File file = new File(path + "download/" + "download.pdf");   
  
        try {   
            FileInputStream inputStream = new FileInputStream(file);   
  
            //3.通过response获取ServletOutputStream对象(out)   
            out = response.getOutputStream();   
  
            int b = 0;   
            byte[] buffer = new byte[512];   
            while (b != -1){   
                b = inputStream.read(buffer);   
                //4.写到输出流(out)中   
                out.write(buffer,0,b);   
            }   
            inputStream.close();   
            out.close();   
            out.flush();   
  
        } catch (IOException e) {   
            e.printStackTrace();   
        }   
    }   
  
    @Override  
    public void setServletContext(ServletContext servletContext) {   
        this.servletContext = servletContext;   
    }   
}