小白学Java24:JDBC
环境搭建
eclipse：
- 找到对应的MySQL版本的JDBC库
- 在项目下新建源文件夹：lib
- 把库复制到lib文件夹下，
- 拖动lib 复制文件夹，生成路径—>配置路径
- 顶部复制“库”，右侧添加JAR，找到刚刚复制到lib文件夹里的库
- 应用并关闭
可能会出现的错误：
- 时区错误：
- 解决方法1：连接时设置时区字符串URL =jdbc:mysql://localhost:3306/books ?serverTimezone=UTC;
- 解决方法2：修改默认时区 mysql> set global time_zone =’+ 8:00’;
开发步骤
1.加载驱动
class.forName "com.mysql.cj.jdbc.Driver"）;
2.连接到数据库
获得连接
String url = "jdbc:mysql://localhost:3306/companydb";
String user = "root";
String password = "1234";
Connection conn = DriverManager.getConnection(url,user,password);
测试是否连接成功
if(conn!= null) {
System.out.println("连接到数据库");
}else {
System.out.println("连接失败");
}
3. 获取发送SQL语句的对象
Statement Statement = conn.createStatement();
4. 执行SQL语句
DML操作(增删改): 返回的是受影响行数(int)
Statement.executeUpdate(Sql语句)
//增
String sql = "insert into test values(2,'张三');";
//删
String sql = "delete from test where id = 1;";
//改
String sql = "update test set name = '测试'where id = 1;";
int executeUpdate = Statement.executeUpdate(sql);
DQL(查询操作) :返回的是ResultSet字符集
String sql2 = "select * from test;";
ResultSet executeQuery = Statement.executeQuery(sql2);
5. 处理接收结果
if(executeUpdate == 1) {
System.out.println("执行成功");
}else System.out.println("执行失败");
6. 释放资源
statement.close();
conn.close();
ResultSet(查询得到的结果集)
接收结果集
String sql2 = "select * from test;";
ResultSet rs= Statement.executeQuery(sql2);
遍历ResultSet中的数据
// 根据列号 来遍历
while (re.next()) {
int id = re.getInt(1);
String name = re.getString(2);
System.out.println(id + "\t" + name);
}
// 根据列名 来遍历
while (re.next()) {
int id = re.getInt("id");
String name = re.getString("name");
System.out.println(id + "\t" + name);
}
小练习
编写用户注册程序
public static void main(String[] args) throws Exception {
String driver = "com.mysql.cj.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/test";
String user = "root";
String password = "1234";
Connection conn = null;
Class.forName(driver);
conn = DriverManager.getConnection(url, user, password);
Statement statement = conn.createStatement();
Scanner sc = new Scanner(System.in);
System.out.println("欢迎注册~");
boolean flag = false;
String username = null;
while (!flag) {
System.out.println("请输入用户名");
username = sc.next();
flag = checkout(statement, username);
}
System.out.println("请输入密码");
String userpassword = sc.next();
addlogin(statement, username, userpassword);
statement.close();
conn.close();
}
// 用户名是否重复
private static boolean checkout(Statement statement, String str) {
String sql = "select name from user;";
try {
ResultSet rs = statement.executeQuery(sql);
while (rs.next()) {
if (rs.getString("name").equals(str)) {
System.out.println("此用户名已经被使用,请重试");
return false;
}
}
return true;
} catch (SQLException e) {
System.out.println("查询语句出错");
e.printStackTrace();
}
return false;
}
//插入到数据库
private static void addlogin(Statement statement, String name, String password) {
String sql = "insert into user(name,password) values('" + name + "','" + password + "');";
try {
statement.executeLargeUpdate(sql);
System.out.println("注册成功");
} catch (SQLException e) {
System.out.println("插入语句出错");
e.printStackTrace();
}
}
编写用户登录程序
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/test";
String user = "root";
String password = "1234";
Connection conn = DriverManager.getConnection(url, user, password);
System.out.println("欢迎登录~");
Scanner sc = new Scanner(System.in);
System.out.println("请输入用户名:");
String username = sc.next();
System.out.println("请输入密码:");
String userpassword = sc.next();
Statement statement = conn.createStatement();
String sql = "select name ,password from user where name ='" + username + "'and password = '" + userpassword
+ "';";
ResultSet rs = statement.executeQuery(sql);
if (rs.next()) {
System.out.println("登录成功");
} else {
System.out.println("登录失败");
}
rs.close();
statement.close();
conn.close();
PreparedStatement｛重点｝:避免SQL注入
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/test";
String user = "root";
String password = "1234";
Connection conn = DriverManager.getConnection(url, user, password);
System.out.println("欢迎登录~");
Scanner sc = new Scanner(System.in);
System.out.println("请输入用户名:");
String username = sc.next();
System.out.println("请输入密码:");
String userpassword = sc.next();
//使用更安全也更快的PreparedStatement
PreparedStatement statement = conn.prepareStatement("select * from user where name = ? and password = ?;");
statement.setString(1, username);
statement.setString(2,userpassword);
ResultSet rs = statement.executeQuery(sql);
if (rs.next()) {
System.out.println("登录成功");
} else {
System.out.println("登录失败");
}
rs.close();
statement.close();
conn.close();
封装工具类
重用性方案
public class JdbcTool {
static {
try {
Class.forName("com.mysql.cj.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public static Connection getConnection() {
Connection conn = null;
String url = "jdbc:mysql://localhost:3306/test?serverTimezone=UTC&characterEncoding=utf-8";
String user = "root";
String password = "1234";
try {
conn = DriverManager.getConnection(url, user, password);
}catch (SQLException e) {
System.out.println("连接失败");
e.printStackTrace();
}
return conn;
}
public static void closeAll(Connection conn, Statement s, ResultSet rs) {
try {
if (conn != null) {
conn.close();
}
if (s != null) {
s.close();
}
if (rs != null) {
rs.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
跨平台方案
public class JDBCUtils {
private static final Properties PROPERTIES = new Properties(); // 存储配置文件的集合
static {
InputStream is = JDBCUtils.class.getResourceAsStream("/db.properties");//把配置文件转换成流
try {
PROPERTIES.load(is);// 通过流,将配置文件加载到properties集合
Class.forName(PROPERTIES.getProperty("driver"));//通过键,获取到driver的值
} catch (IOException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}
public static Connection getConnection() {
Connection conn = null;
try {
conn = DriverManager.getConnection(PROPERTIES.getProperty("url"), PROPERTIES.getProperty("user"),
PROPERTIES.getProperty("password"));
} catch (SQLException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
return conn;
}
public static void closeAll(Connection conn, Statement statement, ResultSet resultSet) {
try {
if (conn != null) {
conn.close();
}
if (statement != null) {
statement.close();
}
if (resultSet != null) {
resultSet.close();
}
} catch (SQLException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}
}
//配置文件:
//文件名: db.properties
driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/test
user=root
password=1234
ORM: 对象关系映射
零散数据整理
一行数据中,多个零散的数据进行整理
通过entity的规则对表中的数据进行对象的封装
entity: 实体类
类名 = 表名, 属性名 = 列名,提供各个属性的get,set方法
提供无参构造方法,(视情况添加有参构造
//创建类 实现 类名=表名,属性名= 列名
//使用工具包,然后把查询到的数据存入实体类集合中
Connection conn = null;
PreparedStatement statement = null;
ResultSet rs = null;
List<User> userList = new ArrayList<>();
conn = JDBCUtils.getConnection();
try {
statement = conn.prepareStatement("select *from test;");
rs = statement.executeQuery();
while (rs.next()) {
int id = rs.getInt("id");
String name = rs.getString("name");
userList.add(new User(id, name));
}
} catch (SQLException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
JDBCUtils.closeAll(conn, statement, rs);
for (User user : userList) {
System.out.println(user);
}
DAO数据访问对象
- DAO实现了业务逻辑和数据库访问的分离
- 对同一张表的所有操作封装在XXXDaoImpl对象中
- 根据增删改查的不同功能实现具体的方法(insert,uodate,delete,select.selectAll)
DAO步骤
- 创建数据表
- 根据数据表封装实体类,类名 = 表名,属性名=列名
- 编写DaoImpl类,提供增删改查的方法
Date工具类
在使用DAO的时候有个问题,数据库的日期类型为java.sql.Date,但是Java程序里的日期类型为Java.util.Date,当我们使用Java程序插入带日期的数据到数据库中时,需要进行转换
字符串\Util.Date\SQL.Date之间的转换
public class DateUtils {
private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
// 字符串转Util.date
public static java.util.Date strToUtilD(String str) {
java.util.Date date = null;
try {
date = sdf.parse(str);
return date;
} catch (ParseException e) {
e.printStackTrace();
}
return date;
}
// util.date转sql.date
public static java.sql.Date utilDToSqlD(java.util.Date date) {
return new java.sql.Date(date.getTime());
}
// date装换为字符串
public static String utilToSql(java.util.Date date) {
return sdf.format(date);
}
}
Service业务
步骤
- 使用ORM编写底层对象关系映射,类名=表名, 属性名=列名
- 编写DaoImpl类,封装数据库操作
- 编写ServiceImpl类,实现业务逻辑
例子:实现转账业务
- 在mysql中创建表并插入数据
CREATE TABLE account(
cardNo VARCHAR(20) PRIMARY KEY,
PASSWORD VARCHAR(20) NOT NULL,
NAME VARCHAR(20) UNIQUE NOT NULL,
balance DOUBLE NOT NULL
)CHARSET = utf8;
INSERT INTO account VALUES( '6001','1234','luyan',10000),( '6002','1234','zhang',10000);
- 编写ORM对象关系映射
public class Account {
private String cardNo;
private String password;
private String name;
private double balance;
public Account() {
}
public Account(String cardNo, String password, String name, double balance) {
super();
this.cardNo = cardNo;
this.password = password;
this.name = name;
this.balance = balance;
}
public String getCardNo() {
return cardNo;
}
public void setCardNo(String cardNo) {
this.cardNo = cardNo;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getBalance() {
return balance;
}
public void setBalance(double balance) {
this.balance = balance;
}
@Override
public String toString() {
return "Account [cardNo=" + cardNo + ", password=" + password + ", name=" + name + ", balance=" + balance + "]";
}
}
- 编写AccountDaoImpl,实现与数据库的交互
public class AccountDaoImpl {
public int insert(Account account) {
return 0;
}
public int delete(String cardNo) {
return 0;
}
// 修改
public int update(Account account) {
Connection conn = null;
PreparedStatement statement = null;
String sql = "update account set password =?,name = ? , balance = ? where cardNo = ?;";
try {
conn = JDBCUtils.getConnection();
statement = conn.prepareStatement(sql);
statement.setString(1, account.getPassword());
statement.setString(2, account.getName());
statement.setDouble(3, account.getBalance());
statement.setString(4, account.getCardNo());
int update = statement.executeUpdate();
return update;
} catch (Exception e) {
e.printStackTrace();
} finally {
JDBCUtils.closeAll(conn, statement, null);
}
return 0;
}
// 查询单个
public Account select(String cardNo) {
Connection conn = null;
PreparedStatement statement = null;
ResultSet rs = null;
Account account = null;
String sql = "select * from account where cardNo = ?;";
try {
conn = JDBCUtils.getConnection();
statement = conn.prepareStatement(sql);
statement.setString(1, cardNo);
rs = statement.executeQuery();
if (rs.next()) {
String cardNos = rs.getString("cardNo");
String password = rs.getString("password");
String name = rs.getString("name");
double balance = rs.getDouble("balance");
account = new Account(cardNos, password, name, balance);
}
return account;
} catch (Exception e) {
e.printStackTrace();
}
return account;
}
}
- 编写AccountServiceImpl实现业务逻辑
public class AccountServiceImpl {
// 转账
public void teansfer(String fromNo, String pwd, String toNo, double money) {
AccountDaoImpl ad = new AccountDaoImpl();
try {
// 验证from是否存在
Account from = ad.select(fromNo);
if (from == null) {
throw new RuntimeException("卡号不存在");
}
// 登录fromNo
if (!from.getPassword().equals(pwd)) {
throw new RuntimeException("密码错误!");
}
// 验证余额
if (from.getBalance() < money) {
throw new RuntimeException("余额不足!");
}
// 验证toNo
Account to = ad.select(toNo);
if (to == null) {
throw new RuntimeException("转入账户不存在");
}
// 减少from余额
from.setBalance(from.getBalance() - money);
ad.update(from);
// 增加TONo余额
to.setBalance(to.getBalance() + money);
ad.update(to);
System.out.println("转账成功");
} catch (RuntimeException e) {
e.printStackTrace();
System.out.println("转账失败!");
}
}
}
使用ThreadLocal实现事务的共享
使用事务
conn = JDBCUtils.getConnection();
conn.setAutoCommit(false);//关闭自动提交,开启事务
conn.commit();//提交数据
conn.rollback();//回滚数据
存在问题:
因为Connection不同步所以并不能真正实现回滚
解决方案:ThreadLocal
使用ThreadLocal可以将整个线程中存储一个共享值
//在JDBCUtils中,将当前Connection对象添加到ThreadLocal中
private static ThreadLocal<Connection> threadLocal = new ThreadLocal<>();
public static Connection getConnection() {
Connection conn = threadLocal.get();
try {
if (conn == null) {
conn = DriverManager.getConnection(PROPERTIES.getProperty("url"), PROPERTIES.getProperty("user"),
PROPERTIES.getProperty("password"));
threadLocal.set(conn);
}
} catch (SQLException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
return conn;
}
使用ThreadLocal后的JDBCUtils工具类
private static final Properties PROPERTIES = new Properties(); // 存储配置文件的集合
private static ThreadLocal<Connection> threadLocal = new ThreadLocal<>();
static {
InputStream is = JDBCUtils.class.getResourceAsStream("/db.properties");
try {
PROPERTIES.load(is);// 通过流,将配置文件加载到properties集合
Class.forName(PROPERTIES.getProperty("driver"));
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public static void begin() {
try {
Connection conn = getConnection();
conn.setAutoCommit(false);
} catch (SQLException e) {
e.printStackTrace();
}
}
public static void commit() {
Connection conn = null;
try {
conn = getConnection();
conn.commit();
} catch (SQLException e) {
e.printStackTrace();
} finally {
closeAll(conn, null, null);
}
}
public static void rollback() {
Connection conn = null;
try {
conn = getConnection();
conn.rollback();
} catch (SQLException e) {
e.printStackTrace();
} finally {
closeAll(conn, null, null);
}
}
public static Connection getConnection() {
Connection conn = threadLocal.get();
try {
if (conn == null) {
conn = DriverManager.getConnection(PROPERTIES.getProperty("url"), PROPERTIES.getProperty("user"),
PROPERTIES.getProperty("password"));
threadLocal.set(conn);
}
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
public static void closeAll(Connection conn, Statement statement, ResultSet resultSet) {
try {
if (resultSet != null) {
resultSet.close();
}
if (statement != null) {
statement.close();
}
if (conn != null) {
conn.close();
threadLocal.remove();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
三层架构
-
- 表示层:
命名规则: xxxxView
职责: 收集用户的数据和需求,展示数据
- 表示层:
-
- 业务逻辑层
命名规则: xxxxServiceImpl
职责: 数据加工处理,调用DAO完成业务的实现,控制事务
- 业务逻辑层
-
- 数据访问层
命名规则: xxxxDaoImpl
职责: 向业务层提供数据,将业务层加工后的数据同步到数据库
- 数据访问层
最好使用接口来编写业务逻辑层和数据访问层
连接池:Druid
使用连接池可以实现资源的可重复利用
//需要在配置文件中添加:
initialSize=10//初始连接数
maxActive=30//最大连接数
minIdle=5//最小保存连接数
maxWait=3000//等待可用连接时间
创建连接池
//声明一个私有的连接池对象
private static DruidDataSource ds;
//加载配置文件
Properties properties = new Properties();
InputStream is = DbUtils.class.getResourceAsStream("/db.properties");
properties.load(is);
ds = (DruidDataSource)
//传入配置文件信息到连接池,会自动连接 ds = (DruidDataSource)DruidDataSourceFactory.createDataSource(properties);
//获取连接对象
Connection con = ds.getConnecton();
//放回连接池
con.close();
基于Apache的DbUtils
//使用apache提供的QueryRunner类,来执行SQL语句
private static QueryRunner qr = new QueryRunner(DbUtils.getDataSource());//传入一个连接池对象
//执行增删改语句:
qr.update(String sql)
//执行查询语句
qr.query(String sql);
private static QueryRunner qr = new QueryRunner(DbUtils.getDataSource());
// 增
private static int insert(User user) {
Object[] o = { user.getUid(), user.getUname(), user.getUpassword(), user.getUstate(), user.getUrole() };
try {
return qr.update("insert into user values(?,?,?,?,?);", o);
} catch (SQLException e) {
e.printStackTrace();
}
return 0;
}
// 删
private static int delete(int id) {
try {
return qr.update("delete from user where uid = ?;", id);
} catch (SQLException e) {
e.printStackTrace();
}
return 0;
}
// 改:
private static int update(User user) {
Object[] o = { user.getUname(), user.getUpassword(), user.getUstate(), user.getUrole(), user.getUid() };
try {
return qr.update("update user set uname = ?,upassword = ?,ustate=?,urole =? where uid = ? ;", o);
} catch (SQLException e) {
e.printStackTrace();
}
return 0;
}
// 查
private static User select(int id) {
try {
// 把查询到的数据封装成指定对象
return qr.query("select * from user where uid = ?;", new BeanHandler<User>(User.class), id);
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
// 查所有
private static List<User> selectAll() {
try {
return qr.query("select * from user;", new BeanListHandler<User>(User.class));
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}