java - 点击图片下载图片

Question

我想点击下载图片。我已经设置了内容类型，但我无法编写图像作为响应。在控制器中，我得到图像的 URL。

String image=myimageUrl;
File file = new File(image);  
String contentType = getServletContext().getMimeType(file.getName());
response.setBufferSize(DEFAULT_BUFFER_SIZE);
response.setContentType(contentType);
response.setHeader("Content-Length", String.valueOf(file.length()));

为了写入响应，我使用了这段代码

DataInputStream input = new DataInputStream(new FileInputStream(file));
ServletOutputStream output  = response.getOutputStream();

这里输入返回null。

如何解决这个问题？

Answer 1

请检查以下代码。

用于将图像上传到数据库。

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
                    String path=request.getParameter("h2");
                    out.println(path);
                    Connection connection=null;
                    ResultSet rs = null;
                    PreparedStatement psmnt = null;
                    FileInputStream fis;
                    Class.forName("com.mysql.jdbc.Driver");
                    connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/image", "root", "kshitij");
                File image = new File(path);
                    psmnt = connection.prepareStatement("insert into new1(id,imagepath)"+"values(?,?)");
                    String s1=request.getParameter("h1");
                    psmnt.setString(1,s1);
                    fis = new FileInputStream(image);
                    psmnt.setBinaryStream(2, (InputStream)fis, (int)(image.length()));

               int s = psmnt.executeUpdate();
               if(s>0) {
                      out.println("Uploaded successfully !");
               }
               else {
              out.println("unsucessfull to upload image.");
               }
           }
           catch (Exception ex) {
                  System.out.println("Found some error : "+ex);
           }

并用于下载图像。

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        //response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();

            Connection connection = null;
            ResultSet rs = null;
            PreparedStatement psmnt = null;
        InputStream sImage;

            try {
                    Class.forName("com.mysql.jdbc.Driver").newInstance();
                    connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/image", "root", "kshitij");
                    psmnt = connection.prepareStatement("SELECT imagepath FROM new1 WHERE id = ?");
                    psmnt.setString(1, "23");
                    rs = psmnt.executeQuery();
                if(rs.next()) {
                      byte[] bytearray = new byte[1048576];
                      int size=0;
                      sImage = rs.getBinaryStream(1);
                      //response.reset();
                      response.setContentType("image/jpeg");
                      while((size=sImage.read(bytearray))!= -1 ){
                            response.getOutputStream().write(bytearray,0,size);

                      }
                }
            }
            catch(Exception ex){
    //          out.println("error :"+ex);
            }
    }