java - 使用 jsp 和 servlet 将文件存储在 MySql 数据库中。

我正在尝试使用 jsp 和 servlet 将文件(文本或图像)存储在 mySql 数据库中。

这是 index.jsp。

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>File Upload to Database Demo</title>
</head>
<body>
<center>
    <h1>File Upload to Database Demo</h1>
    <form method="post" action="FileUploadDBServlet" enctype="multipart/form-data">
        <table border="0">
            <tr>
                <td>First Name: </td>
                <td><input type="text" name="firstName" size="50"/></td>
            </tr>
            <tr>
                <td>Last Name: </td>
                <td><input type="text" name="lastName" size="50"/></td>
            </tr>
            <tr>
                <td>Portrait Photo: </td>
                <td><input type="file" name="photo" size="50"/></td>
            </tr>
            <tr>
                <td colspan="2">
                    <input type="submit" value="Save">
                </td>
            </tr>
        </table>
    </form>
</center>
</body>
</html>

这是我的 FileUploadDBServlet。

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;


@WebServlet(name = "FileUploadDBServlet", urlPatterns ={"/FileUploadDBServlet"})          
public class FileUploadDBServlet extends HttpServlet {

   // database connection settings
     String dbURL = "jdbc:mysql://localhost:3306/rep";
      String dbUser = "root";
      String dbPass = "";

    protected void doPost(HttpServletRequest request,
    HttpServletResponse response) throws ServletException, IOException {
    // gets values of text fields
    String firstName = request.getParameter("firstName");
   String lastName = request.getParameter("lastName");

   InputStream inputStream=null; // input stream of the upload file

// obtains the upload file part in this multipart request
Part filePart = request.getPart("photo");
if (filePart != null) {
    // prints out some information for debugging
    System.out.println(filePart.getName());
    System.out.println(filePart.getSize());
    System.out.println(filePart.getContentType());

  // obtains input stream of the upload file
     inputStream = filePart.getInputStream();

}
 //System.out.println(inputStream);
Connection conn = null; // connection to the database
String message = null;  // message will be sent back to client

try {
    // connects to the database
    DriverManager.registerDriver(new com.mysql.jdbc.Driver());
    conn = DriverManager.getConnection(dbURL, dbUser, dbPass);

    // constructs SQL statement
    String sql = "INSERT INTO contacts (first_name, last_name, photo) values (?, ?, ?)";
    PreparedStatement statement = conn.prepareStatement(sql);

    statement.setString(1, firstName);
    statement.setString(2, lastName);

   if (inputStream != null) {
        // fetches input stream of the upload file for the blob column
        statement.setBlob(3, inputStream);
   }

    // sends the statement to the database server
    int row = statement.executeUpdate();
    if (row > 0) {
        message = "File uploaded and saved into database";
    }
} catch (SQLException ex) {
    message = "ERROR: " + ex.getMessage();
    ex.printStackTrace();
} finally {
    if (conn != null) {
        // closes the database connection
        try {
            conn.close();
        } catch (SQLException ex) {
            ex.printStackTrace();
        }
    }
    // sets the message in request scope
    request.setAttribute("Message", message);

    // forwards to the message page
    getServletContext().getRequestDispatcher("/Message.jsp").forward(request, response);
}
}
}

这是我的 Message.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
     pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd"/>

 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"/>
 <title>Message</title>
 </head>
 <body>
 <center>
      <h3><%=request.getAttribute("Message")%></h3>
 </center>
 </body>
 </html>

消息页面显示“错误:没有为参数 3 指定值”。所以，我认为 null 值存储在 inputStream 中。为什么会这样，如何处理？谢谢。

最佳答案

如果您的输入流为空，您可以使用 statement.setNull(3, java.sql.Types.BLOB);。

if (inputStream != null) {
    // fetches input stream of the upload file for the blob column
    statement.setBlob(3, inputStream);
} else {
    statement.setNull(3, java.sql.Types.BLOB);
}

关于java - 使用 jsp 和 servlet 将文件存储在 MySql 数据库中。，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29620451/

java - 使用 jsp 和 servlet 将文件存储在 MySql 数据库中。

上一篇：带有 Join 和 union all 的 mysql 查询

下一篇：mysql - 如何使连接表条目唯一？