JavaWeb技术（二）：DAO设计模式

1. DAO全称：Data Access Object , 数据访问对象。使用DAO设计模式来封装数据持久化层的所有操作(CRUD)，使得数据访问逻辑和业务逻辑分离，实现解耦的目的。

2. 典型的DAO实现组件：DAO接口 + DAO接口的实现类

3. 事例代码

　　1）javabean组件：用于数据传输的对象

/** javabean数据传输对象 */
public class Customer {
    // 和数据库中的表是对应的
    private int id;
    private String name;
    private String email;

    // 省略getter()/setter()方法

    @Override
    public String toString() {
        return id + ", " + name + ", " + email;
    }
}

　　2）DAO接口

/** DAO接口，用于定义application访问数据库的通用方法  */
public interface CustomerDemo {
    // CRUD
    public void add(Customer c);
    public void update(Customer    c);
    public void delete(int id);
    public Customer getCustomerById(int id);
    public List<Customer> queryList();

}

　　3）DAO接口的实现类

 package com.znker.jdbc;

 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.ArrayList;
 import java.util.List;

 // DAO接口的实现类

 public class CustomerDaoImpl implements CustomerDemo {

     @Override
     public void add(Customer c) {
         String sql = "insert into CustomerTb1(name,email) values(?,?)";
         // 获得一个数据库连接对象
         Connection conn = DBUtil2.open();

         try {
             // 预定义语句对象
             PreparedStatement pstmt = conn.prepareStatement(sql);
             // 对占位符进行赋值
             pstmt.setString(1, c.getName());
             pstmt.setString(2, c.getEmail());
             // 执行添加操作
             pstmt.executeUpdate();

         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             DBUtil2.close(conn);
         }
     }

     @Override
     public void update(Customer c) {
         String sql = "update CustomerTb1 set name=?, email=? where id=?";
         Connection conn = DBUtil2.open();

         try {
             PreparedStatement pstmt = conn.prepareStatement(sql);
             pstmt.setInt(3, c.getId());
             pstmt.setString(1, c.getName());
             pstmt.setString(2, c.getEmail());

             pstmt.executeUpdate();

         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             DBUtil2.close(conn);
         }
     }

     @Override
     public void delete(int id) {
         String sql = "delete from CustomerTb1 where id = ?";
         Connection conn = DBUtil2.open();

         try {
             PreparedStatement pstmt = conn.prepareStatement(sql);
             pstmt.setInt(1, id);

             pstmt.executeUpdate();

         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             DBUtil2.close(conn);
         }
     }

     @Override
     public Customer getCustomerById(int id) {
         String sql = "select id, name, email from CustomerTb1 where id = ?";
         Connection conn = DBUtil2.open();

         try {
             PreparedStatement pstmt = conn.prepareStatement(sql);
             pstmt.setInt(1, id);

             ResultSet rs = pstmt.executeQuery();

             if (rs.next()) {
                 String name = rs.getString(2);
                 String email = rs.getString("email");

                 Customer c = new Customer();
                 c.setId(id);
                 c.setName(name);
                 c.setEmail(email);

                 return c;
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }

         return null;
     }

     @Override
     public List<Customer> queryList() {
         String sql = "select id, name, email from CustomerTb1 ";
         Connection conn = DBUtil2.open();

         try {
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery(sql);
             List<Customer> list = new ArrayList<Customer>();

             while (rs.next()) {
                 int id = rs.getInt(1);
                 String name = rs.getString(2);
                 String email = rs.getString("email");

                 Customer c = new Customer();
                 c.setId(id);
                 c.setName(name);
                 c.setEmail(email);

                 list.add(c);
             }

             return list;
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             DBUtil2.close(conn);
         }

         return null;
     }

 }

　　4）测试代码

import java.util.ArrayList;
import java.util.List;

public class DaoTest {

    public static void main(String[] args) {

        // DAO接口的实现对象，用户业务层访问数据库
        CustomerDemo dao = new CustomerDaoImpl();

        // 添加一个用户
        Customer c = new Customer();
        c.setName("bobo");
        c.setEmail("bobo@qq.com");
        dao.add(c);

        // 查询一个用户List
        List<Customer> list = new ArrayList<Customer>();
        list = dao.queryList();
        System.out.println(list);

    }
}