【新手入门】JDBC+Servlet+jsp【新闻系统的增删改查】：持续学习，持续优化，争取做一个真正的新闻系统出来！

新闻的增删改查

学习了一些博客知识【结尾会贴上，大家可以参考】在借鉴的基础上又进行了代码的优化，从而实现了CRUD，下面分享我的代码过程：

包结构，是为了方便管理，所以我们要这样进行设计：

在数据库进行表结构的插入和设计：（目前小辣鸡制作了新闻的crud）

接着我们进行类的实现，即完善domain类

public class NoteEntity {
    private int id;
    private String type;
    private String text;

    public NoteEntity() {
    }

    public NoteEntity(int id, String type, String text) {
        this.id = id;
        this.type = type;
        this.text = text;
    }

    @Override
    public String toString() {
        return "NoteEntity{" +
                "id='" + id + '\'' +
                ", type='" + type + '\'' +
                ", text='" + text + '\'' +
                '}';
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }
}

实现了类的实现，接着进行数据库的连接（根据我查到的资料，应该是封闭在一个jdbc.Properties文件中是最好的，但我还没做）

public class jdbcUtil {
    public static final String url = "jdbc:mysql://localhost:3306/*?useSSL=false&serverTimezone=UTC";
    public static final String user = "******";
    public static final String password = "******";
    public static final String DRIVER = "com.mysql.cj.jdbc.Driver";

    /**
     * 获取Connection对象
     *
     * @return
     */
     static  {
        try {
            Class.forName(DRIVER);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    public static Connection getConnection() {
        try {
            return DriverManager.getConnection(url, user, password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
//    /**
//     * 释放资源
//     */
    public static void ReleaseResource(Connection connection, PreparedStatement pstm, ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (pstm != null) {
            try {
                pstm.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (connection != null) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

然后进行crud代码的实现

（建议写一个接口类，会方便很多）

public Connection conn1=null;
    public ResultSet rs=null;
    public PreparedStatement ps=null;
//查询所有的数据
    @Override
    public List<NoteEntity> queryAllData() {
        conn1=jdbcUtil.getConnection();//连接数据库
        List<NoteEntity> list=new ArrayList<NoteEntity>();
        try{
            String sql="select * from note";//查询多条数据
            ps=conn1.prepareStatement(sql);
            rs=ps.executeQuery();
            NoteEntity note=null;
            while(rs.next()){
                note =new NoteEntity();
                note.setId(Integer.parseInt(rs.getString("id")));
                note.setType(rs.getString("type"));
                note.setText(rs.getString("text"));
                list.add(note);
            }
        }catch (SQLException e){
            e.printStackTrace();
        }finally {
            jdbcUtil.ReleaseResource(conn1,ps,rs);
        }
        return list;
    }

    //新增
    @Override
    public int insertData(NoteEntity note) {
        conn1=jdbcUtil.getConnection();
        int i=0;
        try{
            String sql="insert into note(type,text) values(?,?)";
            ps=conn1.prepareStatement(sql,PreparedStatement.RETURN_GENERATED_KEYS);
//            ps.setObject(1,note.getId());
            ps.setObject(1,note.getType());
            ps.setObject(2,note.getText());
            ps.executeUpdate();
            rs=ps.getGeneratedKeys();//得到最新的ID
            if(rs.next()){
                i=rs.getInt(1);
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            jdbcUtil.ReleaseResource(conn1,ps,rs);
        }
        return i;
    }
//修改
    @Override
    public int updateData(NoteEntity note) {
        conn1=jdbcUtil.getConnection();
        int i=0;
        try{
            String sql="update note set type=?,text=? where id=?";
            ps=conn1.prepareStatement(sql);
            ps.setObject(1,note.getType());
            ps.setObject(2,note.getText());
            ps.setInt(3,note.getId());
            i=ps.executeUpdate();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            jdbcUtil.ReleaseResource(null,ps,rs);
        }
        return i;
    }

    @Override
    public int deleteData(int id) {
        conn1=jdbcUtil.getConnection();
        int i=0;
        try{
            String sql="delete from note where id=?";
            ps=conn1.prepareStatement(sql);
            ps.setInt(1,id);
            i=ps.executeUpdate();
                    if(i==1){
                        return i;
                    }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            jdbcUtil.ReleaseResource(null,ps,rs);
        }
        System.out.println("未找到数据！");
        return i;
    }
//查询一条数据通过ID
    @Override
    public NoteEntity queryDataById(int id) {
        conn1=jdbcUtil.getConnection();
        NoteEntity note=null;
        if(id>0) {
            try {
                String sql = "select * from note where id=?";
                ps = conn1.prepareStatement(sql);
                ps.setObject(1, id);
                rs = ps.executeQuery();
                if (rs.next()) {
                    note = new NoteEntity();
                    note.setId(rs.getInt("id"));
                    note.setType(rs.getString("type"));
                    note.setText(rs.getString("text"));
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                jdbcUtil.ReleaseResource(null, ps, rs);
            }
        }
        return note;

接着做service层和servlet层

 public Connection conn=null;
    public ResultSet rs=null;
    public PreparedStatement ps=null;
    boolean b=false;
//    这里service层要想与dao层建立联系那么必须创建dao层的对象
    NoteDao note=new NoteDaoImpl();
    //    查询所有的数据
        @Override
        public List<NoteEntity> queryAllData() {
            return note.queryAllData();
        }
    //    新增
    @Override
    public Boolean insertData(NoteEntity no) {
            if(no!=null) {
                note.insertData(no);
                b = true;
            }
        return b;
    }
//    修改
    @Override
    public Boolean updateData(NoteEntity no) {
            if(no!=null) {
                note.updateData(no);
                b=true;
            }
            return b;
    }
//    删除
    @Override
    public Boolean deleteData(int id) {
        if(id!=0) {
            note.deleteData(id);
            b=true;
        }
            return b;
    }
//    查询一条数据
    @Override
    public NoteEntity queryDataById(int id) {
        if (id != 0) {
          return note.queryDataById(id);
        }
        else {
            return null;
        }
    }

 private static final long serialVersionUID = 1l;
    //    建立一个service对象,为了与service层建立联系
    NoteService note = new NoteServiceImpl();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        req.setCharacterEncoding("UTF-8");//防止乱码
        String type = req.getParameter("action");

//        新增
        if ("Insert".equals(type)) {
            insert(req, resp);
        } else if ("Update".equals(type)) {
            update(req, resp);
        } else if ("QueryById".equals(type)) {
            queryById(req, resp);
        } else if ("Delete".equals(type)) {
            delete(req, resp);
        } else if ("QueryAll".equals(type)) {
            queryAll(req, resp);
        }
    }

    public void insert(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//        Integer id = Integer.valueOf(request.getParameter("id"));

        String type = request.getParameter("type");
        String text = request.getParameter("text");
//        把这些获取的值放到note里面
        NoteEntity no = new NoteEntity();
//        no.setId(id);
        no.setType(type);
        no.setText(text);
//        最后调用服务来添加
        String msg = null;
        if (note.insertData(no) == true) {
            queryAll(request, response);
        } else {
            msg = "新增失败!!!";
            request.getRequestDispatcher("/index.jsp").forward(request, response);
        }
    }

    public void update(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//        Integer id = Integer.valueOf(request.getParameter("id"));
        int id= Integer.parseInt(request.getParameter("id"));
        String type = request.getParameter("type");
        String text = request.getParameter("text");
        NoteEntity no = new NoteEntity();
        no.setId(id);
        no.setType(type);
        no.setText(text);
        boolean b = note.updateData(no);
        if (b) {
            queryAll(request, response);
        } else {
            request.setAttribute("msg", "修改失败!!");
            request.getRequestDispatcher("/index.jsp").forward(request, response);
        }
    }

    public void queryById(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        NoteEntity no = null;
//Integer id= Integer.valueOf(request.getParameter("id"));
        int id= Integer.parseInt(request.getParameter("id"));
        System.out.println(id);
        no = note.queryDataById(id);
        request.setAttribute("note", no);
        request.getRequestDispatcher("/note.jsp").forward(request, response);
    }

    public void delete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//        Integer id = Integer.valueOf(request.getParameter("id"));
//        System.out.println(id);
        String id=request.getParameter("id");
//        boolean message=note.deleteData(id);
        boolean message= note.deleteData(Integer.parseInt(id));
        if(message==true){
            queryAll(request,response);
        }else {
            request.setAttribute("msg","删除失败!!!");
            request.getRequestDispatcher("/index.jsp").forward(request,response);
        }
    }

    public void queryAll(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<NoteEntity> list = note.queryAllData();
        request.setAttribute("list", list);
        request.getRequestDispatcher("note.jsp").forward(request, response);
    }

这样就实现了最基本的增删改查了！

那么记下来我想要优化的目标有：

1、实现css的样式美化

2、优化数据库连接代码

3、功能更加完善（创建多个页面实现页面之间的跳转）

4、为了更好的管理jar包，学会maven

5、创建baseDao和baseServlet类

持续更新中...