javaweb上传图片到数据库

在JavaWeb中上传图片到数据库需要进行以下几个步骤：

1.在数据库中创建表，其中包含一个用于存储图片的BLOB类型的字段。

2.在JSP页面中添加一个表单，用于上传图片。

3.在Servlet中获取表单数据，包括上传的图片。

4.将图片转换为字节数组，并将其存储到数据库中。

5.在JSP页面中显示从数据库中检索到的图片。

以下是一个简单的示例代码：

1.创建数据库表

CREATE TABLE `image` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `data` longblob,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

2.添加上传表单

<form action="upload" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="Upload">
</form>

3.处理上传请求

@WebServlet("/upload")
@MultipartConfig
public class UploadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        InputStream inputStream = null;
        OutputStream outputStream = null;
        Connection connection = null;
        PreparedStatement statement = null;
        try {
            Part filePart = request.getPart("file");
            if (filePart != null) {
                inputStream = filePart.getInputStream();
                Class.forName("com.mysql.jdbc.Driver");
                connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
                statement = connection.prepareStatement("INSERT INTO image (name, data) values (?, ?)");
                statement.setString(1, filePart.getName());
                statement.setBlob(2, inputStream);
                statement.executeUpdate();
            }
            response.sendRedirect("index.jsp");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
            if (outputStream != null) {
                outputStream.close();
            }
            if (statement != null) {
                statement.close();
            }
            if (connection != null) {
                connection.close();
            }
        }
    }
}

4.从数据库中检索图片并显示

@WebServlet("/image")
public class ImageServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Connection connection = null;
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        OutputStream outputStream = null;
        try {
            int id = Integer.parseInt(request.getParameter("id"));
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            statement = connection.prepareStatement("SELECT * FROM image WHERE id = ?");
            statement.setInt(1, id);
            resultSet = statement.executeQuery();
            if (resultSet.next()) {
                Blob blob = resultSet.getBlob("data");
                byte[] bytes = blob.getBytes(1, (int) blob.length());
                response.setContentType("image/jpeg");
                outputStream = response.getOutputStream();
                outputStream.write(bytes);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (outputStream != null) {
                outputStream.close();
            }
            if (resultSet != null) {
                resultSet.close();
            }
            if (statement != null) {
                statement.close();
            }
            if (connection != null) {
                connection.close();
            }
        }
    }
}