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

  1 package com.znker.jdbc;
  2
  3 import java.sql.Connection;
  4 import java.sql.PreparedStatement;
  5 import java.sql.ResultSet;
  6 import java.sql.SQLException;
  7 import java.sql.Statement;
  8 import java.util.ArrayList;
  9 import java.util.List;
 10
 11 // DAO接口的实现类
 12
 13 public class CustomerDaoImpl implements CustomerDemo {
 14
 15     @Override
 16     public void add(Customer c) {
 17         String sql = "insert into CustomerTb1(name,email) values(?,?)";
 18         // 获得一个数据库连接对象
 19         Connection conn = DBUtil2.open();
 20
 21         try {
 22             // 预定义语句对象
 23             PreparedStatement pstmt = conn.prepareStatement(sql);
 24             // 对占位符进行赋值
 25             pstmt.setString(1, c.getName());
 26             pstmt.setString(2, c.getEmail());
 27             // 执行添加操作
 28             pstmt.executeUpdate();
 29
 30         } catch (SQLException e) {
 31             e.printStackTrace();
 32         } finally {
 33             DBUtil2.close(conn);
 34         }
 35     }
 36
 37     @Override
 38     public void update(Customer c) {
 39         String sql = "update CustomerTb1 set name=?, email=? where id=?";
 40         Connection conn = DBUtil2.open();
 41
 42         try {
 43             PreparedStatement pstmt = conn.prepareStatement(sql);
 44             pstmt.setInt(3, c.getId());
 45             pstmt.setString(1, c.getName());
 46             pstmt.setString(2, c.getEmail());
 47
 48             pstmt.executeUpdate();
 49
 50         } catch (SQLException e) {
 51             e.printStackTrace();
 52         } finally {
 53             DBUtil2.close(conn);
 54         }
 55     }
 56
 57     @Override
 58     public void delete(int id) {
 59         String sql = "delete from CustomerTb1 where id = ?";
 60         Connection conn = DBUtil2.open();
 61
 62         try {
 63             PreparedStatement pstmt = conn.prepareStatement(sql);
 64             pstmt.setInt(1, id);
 65
 66             pstmt.executeUpdate();
 67
 68         } catch (SQLException e) {
 69             e.printStackTrace();
 70         } finally {
 71             DBUtil2.close(conn);
 72         }
 73     }
 74
 75     @Override
 76     public Customer getCustomerById(int id) {
 77         String sql = "select id, name, email from CustomerTb1 where id = ?";
 78         Connection conn = DBUtil2.open();
 79
 80         try {
 81             PreparedStatement pstmt = conn.prepareStatement(sql);
 82             pstmt.setInt(1, id);
 83
 84             ResultSet rs = pstmt.executeQuery();
 85
 86             if (rs.next()) {
 87                 String name = rs.getString(2);
 88                 String email = rs.getString("email");
 89
 90                 Customer c = new Customer();
 91                 c.setId(id);
 92                 c.setName(name);
 93                 c.setEmail(email);
 94
 95                 return c;
 96             }
 97         } catch (SQLException e) {
 98             e.printStackTrace();
 99         }
100
101         return null;
102     }
103
104     @Override
105     public List<Customer> queryList() {
106         String sql = "select id, name, email from CustomerTb1 ";
107         Connection conn = DBUtil2.open();
108
109         try {
110             Statement stmt = conn.createStatement();
111             ResultSet rs = stmt.executeQuery(sql);
112             List<Customer> list = new ArrayList<Customer>();
113
114             while (rs.next()) {
115                 int id = rs.getInt(1);
116                 String name = rs.getString(2);
117                 String email = rs.getString("email");
118
119                 Customer c = new Customer();
120                 c.setId(id);
121                 c.setName(name);
122                 c.setEmail(email);
123
124                 list.add(c);
125             }
126
127             return list;
128         } catch (SQLException e) {
129             e.printStackTrace();
130         } finally {
131             DBUtil2.close(conn);
132         }
133
134         return null;
135     }
136
137 }

　　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("[email protected]");
        dao.add(c);

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

    }
}