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<Hero> list();
//分页查询
public List<Hero> 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<Hero> list() {
return list(0, Short.MAX_VALUE);
}
public List<Hero> list(int start, int count) {
List<Hero> heros = new ArrayList<Hero>();
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;
}
}
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