1、DAO
Date Access Object，封装了数据访问的逻辑，调用者(一般是业务逻辑模块)不需要了解封装的细节，当细节发生改变时，不会影响调用者。
优势：提升代码的扩展性，方便后期维护。
2、如何写一个DAO
第一步：定义实体类
属性与表字段一一对应，并且提供get/set方法
第二步：定义DAO接口
定义一些与具体技术无关的方法
ResultSet findAll() throws Exception();//JDBC相关
List<Emp> findAll() throws SQLException();//JDBC相关
List<Emp> findAll() throws Exception();//OK
第三步：接口的实现类
使用具体的技术重写接口当中的方法
案例练习：请使用DAO对emp表增删改查功能改写
//步骤一：定义实体类（属性与表字段一一对应，并且提供get/set方法） public class Emp { private int id; private String name; private double salary; private int age; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public double getSalary() { return salary; } public void setSalary(double salary) { this.salary = salary; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public Emp() { super(); } public Emp(String name, double salary, int age) { super(); this.name = name; this.salary = salary; this.age = age; } public Emp(int id, String name, double salary, int age) { super(); this.id = id; this.name = name; this.salary = salary; this.age = age; } } //步骤二：定义DAO接口（定义一些与具体技术无关的方法） public interface EmpDAO { //查找所有的记录 List<Emp> findAll() throws Exception; //删除记录 void delete(int id) throws Exception; //添加 void add(Emp addEmp) throws Exception; //根据id查找某一记录 Emp findById(int id) throws Exception; //更新 void update(Emp emp) throws Exception; } //为了提高代码的复用性，将数据库的连接与关闭代码进行封装 public class DBUtil { //获取连接 public static Connection getConnection() { Connection con = null; try { Class.forName("com.mysql.jdbc.Driver"); con = DriverManager.getConnection( "jdbc:mysql://localhost:3306/jsd1704","root","1234"); } catch (Exception e) { e.printStackTrace(); } return con; } //关闭连接 public static void close(Connection con) { if (con != null) { try { con.close(); } catch (SQLException e) { e.printStackTrace(); } } } } //步骤三：接口的实现类（使用具体的技术重写接口当中的方法） public class EmpDAOImpl implements EmpDAO{ public List<Emp> findAll() throws Exception { Connection con = DBUtil.getConnection();//获取连接 String sql = "select * from emp"; PreparedStatement ps = con.prepareStatement(sql); ResultSet rs = ps.executeQuery(); List<Emp> list = new ArrayList<Emp>(); Emp emp = null; while(rs.next()){ emp = new Emp(); emp.setId(rs.getInt("id")); emp.setName(rs.getString("name")); emp.setSalary(rs.getDouble("salary")); emp.setAge(rs.getInt("age")); list.add(emp); } DBUtil.close(con);//关闭连接 return list; } public void delete(int id) throws Exception { Connection con = DBUtil.getConnection(); String sql = "delete from emp where id=?"; PreparedStatement ps = con.prepareStatement(sql); ps.setInt(1, id); ps.executeUpdate(); DBUtil.close(con); } public void add(Emp addEmp) throws Exception { Connection con = DBUtil.getConnection(); String sql = "insert into emp values(null,?,?,?)"; PreparedStatement ps = con.prepareStatement(sql); ps.setString(1, addEmp.getName()); ps.setDouble(2, addEmp.getSalary()); ps.setInt(3, addEmp.getAge()); ps.executeUpdate(); DBUtil.close(con); } public Emp findById(int id) throws Exception { Connection con = DBUtil.getConnection(); String sql = "select * from emp where id=?"; PreparedStatement ps = con.prepareStatement(sql); ps.setInt(1, id); ResultSet rs = ps.executeQuery(); Emp emp = new Emp(); if (rs.next()) { emp.setName(rs.getString("name")); emp.setSalary(rs.getDouble("salary")); emp.setAge(rs.getInt("age")) ; } DBUtil.close(con); return emp; } public void update(Emp emp) throws Exception { Connection con = DBUtil.getConnection(); String sql = "update emp set name=?,salary=?,age=? where id=?"; PreparedStatement ps = con.prepareStatement(sql); ps.setString(1, emp.getName()); ps.setDouble(2, emp.getSalary()); ps.setInt(3, emp.getAge()); ps.setInt(4, emp.getId()); ps.executeUpdate(); DBUtil.close(con); } } //以增加员工组件AddEmpServlet组件为例，演示增功能 public class AddEmpServlet extends HttpServlet{ public void service(HttpServletRequest req,HttpServletResponse res) throws IOException,ServletException{ req.setCharacterEncoding("utf-8");//设置请求编码格式 res.setContentType("text/html;charset=utf-8");//输出编码 PrintWriter out = res.getWriter();//获取输出流 //获取表单里面数据 String name = req.getParameter("name"); double salary = Double.parseDouble(req.getParameter("salary")); int age = Integer.parseInt(req.getParameter("age")); EmpDAO dao = new EmpDAOImpl(); try { Emp addEmp = new Emp(name,salary,age); dao.add(addEmp); //重定向到list页面 res.sendRedirect("list"); } catch (Exception e) { e.printStackTrace(); out.print("系统繁忙，稍后重试！"); } } }
