基于JDBC設(shè)計(jì)DAO的實(shí)例

DAO=DataAccess Object

數(shù)據(jù)訪問(wèn)對(duì)象

實(shí)際上就是運(yùn)用了ORM中的思路，把數(shù)據(jù)庫(kù)相關(guān)的操作都封裝在這個(gè)類里面，其他地方看不到JDBC的代碼

步驟 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);

//刪除

public void delete(int id);

//獲取

public Hero get(int id);

//查詢

public List list();

//分頁(yè)查詢

public List list(int start, int count);

}

步驟 2 : HeroDAO

設(shè)計(jì)類HeroDAO，實(shí)現(xiàn)接口DAO

把驅(qū)動(dòng)的初始化放在了構(gòu)造方法HeroDAO里：

public HeroDAO() {

try {

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

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

}

因?yàn)轵?qū)動(dòng)初始化只需要執(zhí)行一次，所以放在這里更合適，其他方法里也不需要寫了，代碼更簡(jiǎn)潔

提供一個(gè)getConnection方法返回連接

所有的數(shù)據(jù)庫(kù)操作都需要事先拿到一個(gè)數(shù)據(jù)庫(kù)連接Connection，以前的做法每個(gè)方法里都會(huì)寫一個(gè)，如果要改動(dòng)密碼，那么每個(gè)地方都需要修改。 通過(guò)這種方式，只需要修改這一個(gè)地方就可以了。 代碼變得更容易維護(hù)，而且也更加簡(jiǎn)潔。

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;

}

}

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