Question

我有一个删除相册DAO，一个删除相册类和一个删除servlet都连接到数据库，但它仍然没有运行查询，即它没有工作。

以下代码用于删除servlet

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String name = request.getParameter("name");

        DeleteAlbum Album = new DeleteAlbum(name) ;

        AlbumDAO.INSTANCE.delete(Album);

        request.getRequestDispatcher("home.jsp").forward(request, response);
    }

这是删除专辑类

        public class DeleteAlbum {
            String name ;

            public DeleteAlbum(String name){
                super();

                this.name = name;
            }
            public String getName() {
                return name;
            }
            public void setName(String name) {
                this.name = name;
            }

        }

这部分代码连接到数据库

public enum DeleteAlbumDAO {
        INSTANCE;

        public Connection getConnection() {
            Connection con = null ;
            try {
                Class.forName("org.hsqldb.jdbcDriver");
                con = DriverManager.getConnection(
                        "jdbc:hsqldb:hsql://localhost/oneDB", "sa", "");
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }   
            return con ;
        }

        public void delete(Album name)  {       
            try {
                Connection con = getConnection() ;
                Statement stmt = con.createStatement();
                stmt.executeUpdate("Delete from ALBUM WHERE name="+name+"");
                System.out.println("Connection Succesful");
                stmt.close();
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

这是原始ALBUM DAO的代码，我试图按名称删除相册，我添加了albumDAO以测试ti是否已连接但仍然无法正常工作

import model.Album;
import model.DeleteAlbum;

public enum AlbumDAO {
    INSTANCE;

    public Connection getConnection() {
        Connection con = null ;
        try {
            Class.forName("org.hsqldb.jdbcDriver");
            con = DriverManager.getConnection(
                    "jdbc:hsqldb:hsql://localhost/oneDB", "sa", "");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }   
        return con ;
    }

    public void save(Album album) {     
        try {
            Connection con = getConnection() ;
            Statement stmt = con.createStatement();

            stmt.executeUpdate("INSERT INTO ALBUM (name, artist , genre)"
                        + "VALUES ('" + album.getName() + "','"+ album.getArtist() + "','"+ album.getGenre() + "')");
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void delete(DeleteAlbum name)  {     
        try {
            Connection con = getConnection() ;
            Statement stmt = con.createStatement();
            stmt.executeUpdate("Delete from ALBUM WHERE name="+name+"");
            stmt.close();
            con.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Answer 1

您实际上并未将alubum名称传递给预准备语句，因此您需要更改delete方法，如下所示：

public void delete(DeleteAlbum album)  {     
        //Use try with resources as shown below which closes conn & stmt objects
        try(Connection con = getConnection() ;
            PreparedStatement stmt = con.prepareStatement("Delete from ALBUM WHERE name=?")) {

            stmt.setString(1, album.getName());
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

请使用preparedstament setString（），setInt（）等方法以避免SQL injections。您可以参考here

另外，请确保使用try with resources或关闭finally块中的资源，以避免连接泄漏。

我的删除Servlet不会从数据库中删除

1 个答案: