基于JDBC设计DAO的实例

DAO=DataAccess Object

数据访问对象

实际上就是运用了ORM中的思路，把数据库相关的操作都封装在这个类里面，其他地方看不到JDBC的代码

步骤 1 : DAO接口

package jdbc;

import java.util.List;

import charactor.Hero;

public interface DAO{

//增加

public void add(Hero hero);

//修改

public void update(Hero hero);

//删除

public void delete(int id);

//获取

public Hero get(int id);

//查询

public List list();

//分页查询

public List list(int start, int count);

}

步骤 2 : HeroDAO

设计类HeroDAO，实现接口DAO

把驱动的初始化放在了构造方法HeroDAO里：

public HeroDAO() {

try {

Class.forName("com.mysql.jdbc.Driver");

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

}

因为驱动初始化只需要执行一次，所以放在这里更合适，其他方法里也不需要写了，代码更简洁

提供一个getConnection方法返回连接

所有的数据库操作都需要事先拿到一个数据库连接Connection，以前的做法每个方法里都会写一个，如果要改动密码，那么每个地方都需要修改。 通过这种方式，只需要修改这一个地方就可以了。 代码变得更容易维护，而且也更加简洁。

package jdbc;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

import java.util.ArrayList;

import java.util.List;

import charactor.Hero;

public class HeroDAO implements DAO{

public HeroDAO() {

try {

Class.forName("com.mysql.jdbc.Driver");

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

}

public Connection getConnection() throws SQLException {

return DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root",

"admin");

}

public int getTotal() {

int total = 0;

try (Connection c = getConnection(); Statement s = c.createStatement();) {

String sql = "select count(*) from hero";

ResultSet rs = s.executeQuery(sql);

while (rs.next()) {

total = rs.getInt(1);

}

System.out.println("total:" + total);

} catch (SQLException e) {

e.printStackTrace();

}

return total;

}

public void add(Hero hero) {

String sql = "insert into hero values(null,?,?,?)";

try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

ps.setString(1, hero.name);

ps.setFloat(2, hero.hp);

ps.setInt(3, hero.damage);

ps.execute();

ResultSet rs = ps.getGeneratedKeys();

if (rs.next()) {

int id = rs.getInt(1);

hero.id = id;

}

} catch (SQLException e) {

e.printStackTrace();

}

}

public void update(Hero hero) {

String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?";

try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

ps.setString(1, hero.name);

ps.setFloat(2, hero.hp);

ps.setInt(3, hero.damage);

ps.setInt(4, hero.id);

ps.execute();

} catch (SQLException e) {

e.printStackTrace();

}

}

public void delete(int id) {

try (Connection c = getConnection(); Statement s = c.createStatement();) {

String sql = "delete from hero where id = " + id;

s.execute(sql);

} catch (SQLException e) {

e.printStackTrace();

}

}

public Hero get(int id) {

Hero hero = null;

try (Connection c = getConnection(); Statement s = c.createStatement();) {

String sql = "select * from hero where id = " + id;

ResultSet rs = s.executeQuery(sql);

if (rs.next()) {

hero = new Hero();

String name = rs.getString(2);

float hp = rs.getFloat("hp");

int damage = rs.getInt(4);

hero.name = name;

hero.hp = hp;

hero.damage = damage;

hero.id = id;

}

} catch (SQLException e) {

e.printStackTrace();

}

return hero;

}

public List list() {

return list(0, Short.MAX_VALUE);

}

public List list(int start, int count) {

List heros = new ArrayList();

String sql = "select * from hero order by id desc limit ?,? ";

try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {

ps.setInt(1, start);

ps.setInt(2, count);

ResultSet rs = ps.executeQuery();

while (rs.next()) {

Hero hero = new Hero();

int id = rs.getInt(1);

String name = rs.getString(2);

float hp = rs.getFloat("hp");

int damage = rs.getInt(4);

hero.id = id;

hero.name = name;

hero.hp = hp;

hero.damage = damage;

heros.add(hero);

}

} catch (SQLException e) {

e.printStackTrace();

}

return heros;

}

}