使用 servlet 上传后图像文件损坏

Question

I am try uploading the image using the below servlet But after upload I am able save the file but I am not able to open I checked the file is corrupted.

Instead of using the annotation I have describe multipart-config in web.xml. I this code I am trying to get the image file I send the data using AJAX. Then I am redirected to Register servlet there I am using InputStream class to handle data. After this I creating the file and upload this Inputdata to file in some directory on server.

public class Register extends HttpServlet{
    @Override 
    protected void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException,IOException{
        String username=req.getParameter("username");
        String password=req.getParameter("password");
        String email=req.getParameter("email");
        Part part = req.getPart("image");
        String filename = part.getSubmittedFileName();
        InputStream is = req.getInputStream();
        byte[] data = new byte[is.available()];
        String path = "D:\\FullstackWeb\\images\\icon\\"+filename;
        System.out.println(path);
        FileOutputStream fos=new FileOutputStream(path);
        fos.write(data);
        res.setContentType("text/html");
        PrintWriter out = res.getWriter();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection conn = DriverManager.getConnection("jdbc:mysql://dns1.nishchay.com:3306/register","demouser","123Nbr@");
            String query = "Insert INTO register.signup(username,email,userpassword,filename) values(? ,?, ?,?)";
            PreparedStatement pstmt= conn.prepareStatement(query);
            pstmt.setString(1, username);
            pstmt.setString(2, email);
            pstmt.setString(3, password);
            pstmt.setString(4, path);       
            pstmt.executeUpdate();      
            conn.close();
        }catch(Exception e) {
            out.println("<h1>Issue is occured</h1>");       
        }       
    }
}```

Answer 1

You are not reading in the image data:

    InputStream is = req.getInputStream();
    byte[] data = new byte[is.available()];
    String path = "D:\\FullstackWeb\\images\\icon\\"+filename;
    System.out.println(path);
    FileOutputStream fos=new FileOutputStream(path);
    fos.write(data);

does not contain any is.read() call and it doesn't close the FileOutputStream .

In addition to that your allocated buffer is to small for most images. The JavaDoc for InputStream.available() states

Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking

To completely read the image data you could simply replace the above code with

Files.copy(is, Paths.get("D:\\FullstackWeb\\images\\icon\\"+filename));

but with a big caveat : since the file name is supplied by the user of your service this opens your code to security problems.