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网站搭建吧,南宁营销型网站建设公司,建设标准 免费下载网站,网站建设注册什么公司好1 JDBC介绍JDBC : java database connectivity 编写java程序 实现对任意一个DBMS软件的数据进行增删改查#xff0c;都需要使用JDBC JDBC是sun公司发布的一套关于数据库的规范 JDBC实际上就是一套接口#xff0c;各个数据库厂商都需要实现这个接口#xff0c;实…1 JDBC介绍JDBC : java database connectivity 编写java程序 实现对任意一个DBMS软件的数据进行增删改查都需要使用JDBC JDBC是sun公司发布的一套关于数据库的规范 JDBC实际上就是一套接口各个数据库厂商都需要实现这个接口实现这一套接口中的方法 好处:程序员只需要学会JDBC接口就可以调用各个数据库厂商的内容轻松实现增删改查 各个数据库厂商需要提供JDBC接口的实现这些实现统称为 驱动2 获取DBMS的连接用户名 密码 mysql驱动 数据库的ip和端口号和数据库名称2.1 获取连接public class TestDemo { public static void main(String[] args) { // 定义数据库的url jdbc:mysql://ip:端口号/数据库名称 // 如果ip是localhost 端口号是 3306 可以省略 // String url jdbc:mysql://localhost:3306/mydb; String url jdbc:mysql:///mydb; // 用户名 String username root; // 密码 String password root; ​ Connection connection null; try { // 注册驱动(让jvm知道使用的是哪一个DBMS软件) // 在java项目中不需要注册mysql驱动包中存在一个服务发现机制会去META-INF/services/java.sql.Driver文件中的内容自动注册驱动。 // 但是如果是web/maven项目结构中就不能省略 // DriverManager.registerDriver(new Driver()); // 编写代码 获取mysql连接 connection DriverManager.getConnection(url, username, password); System.out.println(connection); } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 if (connection ! null){ try { connection.close(); } catch (SQLException e) { throw new RuntimeException(e); } } } } } ​2.2 获取连接优化注册驱动优化工具类的封装package cn.javasm.utils; ​ import java.io.FileInputStream; import java.io.IOException; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.util.Properties; ​ /** * author : gfs * version : 0.1 * className: DBUtil * date : 2025/12/8 15:05 * description: 数据库相关工具类 * since : jdk17 */ public class DBUtil { ​ private DBUtil(){} ​ private static Properties properties new Properties(); ​ static { // 静态代码块中 读取文件 try { properties.load(new FileInputStream(src/jdbc.properties)); // 注册驱动 Class.forName(properties.getProperty(jdbc.driver)); System.out.println(properties); } catch (IOException e) { throw new RuntimeException(e); } catch (ClassNotFoundException e) { throw new RuntimeException(e); } } ​ ​ /** * 获取连接 * return 连接 */ public static Connection getConncetion(){ Connection connection null; try { connection DriverManager.getConnection(properties.getProperty(jdbc.url), properties.getProperty(jdbc.username), properties.getProperty(jdbc.password)); } catch (Exception e) { throw new RuntimeException(e); } return connection; } ​ /** * 释放连接 * param connection */ public static void release(Connection connection){ if (connection ! null){ try { connection.close(); } catch (SQLException e) { throw new RuntimeException(e); } } } } ​3 CRUD3.1 添加 insertpublic interface UserDao { /** * 添加用户 * return 影响数据库的行数 */ int addUser(); } ​ ​ public class UserDaoImpl implements UserDao { Override public int addUser() { // 获取数据库的连接 Connection conncetion DBUtil.getConncetion(); // 编写sql语句 String sql INSERT INTO user (username,age,password,balance) VALUES (张无忌,20,123456,8899.9); PreparedStatement preparedStatement null; try { // 通过连接 获取预编译对象 preparedStatement conncetion.prepareStatement(sql); // 执行sql语句,返回数据库受影响的行数 int row preparedStatement.executeUpdate(); return row; } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(conncetion,preparedStatement); } } }优化:创建实体类Userpackage cn.javasm.entity; ​ import lombok.Data; import lombok.experimental.Accessors; ​ import java.math.BigDecimal; import java.time.LocalDateTime; ​ /** * author : gfs * version : 0.1 * className: User * date : 2025/12/8 15:41 * description: * since : jdk17 */ Data Accessors(chain true) public class User { /** * 用户标识 */ private Integer id; /** * 用户名 */ private String username; ​ /** * 年龄 */ private Integer age; ​ /** * 密码 */ private String password; ​ /** * 头像 */ private String image; ​ /** * 余额 */ private BigDecimal balance; ​ /** * 创建时间 */ private LocalDateTime createTime; ​ /** * 更新时间 */ private LocalDateTime updateTime; ​ } ​UserDao接口中/** * 添加指定的用户 * return 影响数据库的行数 */ int addUser(User user);UserDaoImpl中Override public int addUser(User user) { // 获取数据库连接 Connection connection DBUtil.getConncetion(); // 编写sql语句 // ? 代表占位符在JDBC中 一个?占一个位置 表示一个数据 String sql insert into user (username,age,password,balance) values (?,?,?,?); PreparedStatement preparedStatement null; try { // 获取预编译对象 preparedStatement connection.prepareStatement(sql); // 给?赋值 // 参数1?所在的位置 从1开始 preparedStatement.setString(1,user.getUsername()); preparedStatement.setInt(2,user.getAge()); preparedStatement.setObject(3,user.getPassword()); preparedStatement.setBigDecimal(4,user.getBalance()); ​ // 执行sql语句 executeUpdate 执行DML insert update delete int row preparedStatement.executeUpdate(); return row; } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement); } }测试类public static void main(String[] args) { Scanner scanner new Scanner(System.in); System.out.println(请输入用户名); String username scanner.next(); System.out.println(请输入密码); String password scanner.next(); System.out.println(请输入年龄); int age scanner.nextInt(); System.out.println(请输入余额); BigDecimal balance scanner.nextBigDecimal(); User user new User().setUsername(username).setAge(age).setPassword(password).setBalance(balance); UserDao userDao new UserDaoImpl(); int row userDao.addUser(user); System.out.println(row 0 ? success : error); }3.2 删除 deletedelete from user where id ?UserDao接口/** * 根据id删除用户 * param id 用户的id * return 受影响的行数 */ int deleteUserById(int id);UserDaoImpl中Override public int deleteUserById(int id) { // 获取连接 Connection connection DBUtil.getConncetion(); // 编写sql语句 String sql DELETE FROM user WHERE id ?; PreparedStatement preparedStatement null; try { // 获取预编译对象 preparedStatement connection.prepareStatement(sql); // 给?赋值 preparedStatement.setInt(1,id); // 执行sql语句 int row preparedStatement.executeUpdate(); return row; } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement); } }3.3 更新 updateupdate user set username ?,age ?,password ? where id ?UserDao接口中/** * 根据id更新用户 * param user 用户 * return 受影响的行数 */ int updateUserById(User user);UserDaoImpl中Override public int updateUserById(User user) { // 获取连接 Connection connection DBUtil.getConncetion(); // 编写sql语句 String sql update user set username ?,age ?, password ? where id ?; // 获取预编译对象 PreparedStatement preparedStatement null; try { preparedStatement connection.prepareStatement(sql); // 给?赋值 preparedStatement.setString(1,user.getUsername()); preparedStatement.setInt(2,user.getAge()); preparedStatement.setString(3,user.getPassword()); preparedStatement.setInt(4,user.getId()); // 执行sql语句 int row preparedStatement.executeUpdate(); return row; } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement); } }3.4 查询3.4.1 根据id查询select * from user where id ?UserDao接口/** * 根据id查询用户 * param id 用户的id * return 查询到的用户 */ User queryUserById(int id);UserDaoImpl中Override public User queryUserById(int id) { // 获取连接 Connection connection DBUtil.getConncetion(); // 编写sql语句 String sql select * from user where id ?; PreparedStatement preparedStatement null; ResultSet resultSet null; try { // 获取预编译对象 preparedStatement connection.prepareStatement(sql); // 给?赋值 preparedStatement.setInt(1,id); // 执行sql语句获取结果集 一行记录是 结果集 中的一个结果 resultSet preparedStatement.executeQuery(); // next() 返回true代表有下一个元素 返回false代表没有下一个元素 if (resultSet.next()){ // 根据位置获取结果的数据 int uid resultSet.getInt(1); // 根据列名获取结果的数据 String username resultSet.getString(username); int age (int) resultSet.getObject(3); String password resultSet.getString(4); String image resultSet.getString(image); BigDecimal balance resultSet.getBigDecimal(6); LocalDateTime createTime (LocalDateTime) resultSet.getObject(7); LocalDateTime updateTime (LocalDateTime) resultSet.getObject(8); User user new User().setId(uid).setUsername(username).setPassword(password).setAge(age).setBalance(balance).setImage(image).setCreateTime(createTime).setUpdateTime(updateTime); return user; } } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement,resultSet); } return null; }3.4.2 查询所有UserDao接口ListUser queryAll();UserDaoImplOverride public ListUser queryAll() { // 获取连接 Connection connection DBUtil.getConncetion(); // 编写sql语句 String sql select * from user; // 获取预编译对象 PreparedStatement preparedStatement null; ResultSet resultSet null; // 创建集合 ListUser list new ArrayList(); try { preparedStatement connection.prepareStatement(sql); // 执行sql语句 resultSet preparedStatement.executeQuery(); while (resultSet.next()){ list.add(getUser(resultSet)); } return list; } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭资源 DBUtil.release(connection,preparedStatement,resultSet); } }3.4.3 分页查询后端需要前端传递的是哪一页 page每页显示多少条 pageSize后端传递给前端的是 当前页的数据 页面的总数量-- 分页查询 select * from user limit ?,? 第一个?: (page - 1) * pageSize 第二个?: pageSize -- 查询总记录数 select count(*) from user;UserDao接口/** * 分页查询 * param page 哪一页 * param pageSize 每页显示的数量 * return */ ListUser queryUserByPage(int page,int pageSize); /** * 查询数据的总数量 用于分页 * return 总数量 */ int queryUserCount();UserDaoImpl类Override public ListUser queryUserByPage(int page, int pageSize) { // 获取连接 Connection connection DBUtil.getConncetion(); // 执行sql语句 String sql select * from user limit ?,?; PreparedStatement preparedStatement null; ResultSet resultSet null; // 创建集合 ListUser list new ArrayList(); try { // 获取预编译对象 preparedStatement connection.prepareStatement(sql); // 给?赋值 preparedStatement.setInt(1,(page - 1) * pageSize); preparedStatement.setInt(2,pageSize); // 执行sql语句 resultSet preparedStatement.executeQuery(); while (resultSet.next()){ list.add(getUser(resultSet)); } return list; } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement,resultSet); } } Override public int queryUserCount() { // 获取连接 Connection connection DBUtil.getConncetion(); // 编写sql String sql select count(*) from user; PreparedStatement preparedStatement null; ResultSet resultSet null; try { // 获取预编译对象 preparedStatement connection.prepareStatement(sql); // 执行sql语句 resultSet preparedStatement.executeQuery(); // 结果集中是总数量 if (resultSet.next()){ return resultSet.getInt(1); } } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement,resultSet); } return 0; }根据条件查询 并分页用户名模糊查询年龄区间查询create_time区间查询3.4.4 根据条件查询 并分页-- 条件 根据用户名模糊搜索 根据年龄在区间范围内搜索 minAge maxAge 根据创建时间在区间范围内搜索 beginTime endTime -- 没有条件 select * from user limit ?,? -- 用户名 select * from user where username like ? limit ?,? -- 用户名 年龄 select * from user where username like ? AND age between ? and ? limit ?,? -- 用户名 年龄 创建时间 select * from user where username like ? AND age between ? and ? AND create_time between ? and ? limit ?,? -- 动态拼接sql语句 where username like ? and age between ? and ? and create_time between ? and ? -- 没有条件 select count(*) from user; -- 用户名 select count(*) from user where username like ? where username like ? and age between ? and ? and create_time between ? and ?UserDao接口中public interface UserDao { /** * 按照条件查询并分页 * param searchParamVo 查询条件 * param page 第几页 * param pageSize 每页显示的数量 * return */ ListUser queryUserByParamAndPage(SearchParamVo searchParamVo,int page,int pageSize); /** * 查询记录的总数量 * param searchParamVo 查询条件 * return 总数量 */ int queryUserByParamCount(SearchParamVo searchParamVo); }UserDaoImpl中public class UserDaoImpl implements UserDao { // where username like ? and age between ? and ? and create_time between ? and ? Override public ListUser queryUserByParamAndPage(SearchParamVo searchParamVo, int page, int pageSize) { // 获取连接 Connection connection DBUtil.getConncetion(); // 编写sql StringBuilder stringBuilder new StringBuilder(select * from user); // 拼接sql appendSql(searchParamVo,stringBuilder); stringBuilder.append( limit ?,? ); String sql stringBuilder.toString(); PreparedStatement preparedStatement null; ResultSet resultSet null; // 创建集合 ListUser list new ArrayList(); try { // 获取预编译对象 preparedStatement connection.prepareStatement(sql); // 给?赋值 int count setParam(searchParamVo, preparedStatement); // 给limit的?赋值 preparedStatement.setInt(count,(page - 1) * pageSize); preparedStatement.setInt(count,pageSize); // 执行sql语句 resultSet preparedStatement.executeQuery(); while (resultSet.next()){ list.add(getUser(resultSet)); } return list; } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement,resultSet); } } private static int setParam(SearchParamVo searchParamVo,PreparedStatement preparedStatement) throws SQLException { // 获取参数 String nameParam searchParamVo.getNameParam(); Integer minAge searchParamVo.getMinAge(); String beginTime searchParamVo.getBeginTime(); Integer maxAge searchParamVo.getMaxAge(); String endTime searchParamVo.getEndTime(); // 记录参数的位置 int count 1; // 用户名 if (nameParam ! null !nameParam.isBlank()){ preparedStatement.setString(count,% nameParam %); } if (minAge ! null){ preparedStatement.setInt(count,minAge); preparedStatement.setInt(count,maxAge); } if (beginTime ! null !beginTime.isBlank()){ preparedStatement.setString(count,beginTime); preparedStatement.setString(count,endTime); } return count; } private static void appendSql(SearchParamVo searchParamVo,StringBuilder stringBuilder){ // 获取参数 String nameParam searchParamVo.getNameParam(); Integer minAge searchParamVo.getMinAge(); String beginTime searchParamVo.getBeginTime(); // 判断是否添加过where true代表添加过 boolean flag false; if (nameParam ! null !nameParam.isBlank()){ stringBuilder.append( where username like ? AND); flag true; } if (minAge ! null){ if (!flag) { stringBuilder.append( where ); flag true; } stringBuilder.append( age BETWEEN ? AND ? AND); } if (beginTime ! null !beginTime.isBlank()){ if (!flag){ stringBuilder.append( where ); flag true; } stringBuilder.append( create_time BETWEEN ? AND ? AND); } if (flag){ // 只要有条件最后必定多一个AND stringBuilder.delete(stringBuilder.lastIndexOf(AND),stringBuilder.length()); } } private static User getUser(ResultSet resultSet) throws SQLException { // 根据位置获取结果的数据 int uid resultSet.getInt(1); // 根据列名获取结果的数据 String username resultSet.getString(username); int age (int) resultSet.getObject(3); String password resultSet.getString(4); String image resultSet.getString(image); BigDecimal balance resultSet.getBigDecimal(6); LocalDateTime createTime (LocalDateTime) resultSet.getObject(7); LocalDateTime updateTime (LocalDateTime) resultSet.getObject(8); User user new User().setId(uid).setUsername(username).setPassword(password).setAge(age).setBalance(balance).setImage(image).setCreateTime(createTime).setUpdateTime(updateTime); return user; } Override public int queryUserByParamCount(SearchParamVo searchParamVo) { // 获取连接 Connection connection DBUtil.getConncetion(); // 拼接sql StringBuilder stringBuilder new StringBuilder(); stringBuilder.append(select count(*) from user ); appendSql(searchParamVo,stringBuilder); PreparedStatement preparedStatement null; ResultSet resultSet null; int totalRow 0; try { // 获取预编译对象 preparedStatement connection.prepareStatement(stringBuilder.toString()); // 给?赋值 setParam(searchParamVo,preparedStatement); // 执行sql语句 resultSet preparedStatement.executeQuery(); if (resultSet.next()){ totalRow resultSet.getInt(1); } } catch (SQLException e) { throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection,preparedStatement,resultSet); } return totalRow; } }3.4.5 多表查询Role类Data Accessors(chain true) public class Role { /** * 角色id */ private Integer id; /** * 角色名称 */ private String roleName; /** * 角色描述 */ private String roleDesc; }Dept类Data Accessors(chain true) public class Dept { /** * 部门id */ private int deptno; /** * 部门名称 */ private String dname; /** * 部门位置 */ private String loc; }UserDao接口中/** * 查询用户 角色和部门信息 * return */ ListUserRoleDept queryUserAndRoleAndDept();UserDaoImpl中Override public ListUserRoleDept queryUserAndRoleAndDept() { // 获取连接 Connection connection DBUtil.getConncetion(); // 编写sql String sql select *\n FROM\n user u,role r,dept d\n WHERE\n u.rid r.id \n AND\n u.deptno d.deptno; PreparedStatement preparedStatement null; ResultSet resultSet null; // 创建集合 ListUserRoleDept list new ArrayList(); try { // 获取预编译对象 preparedStatement connection.prepareStatement(sql); // 执行sql resultSet preparedStatement.executeQuery(); while (resultSet.next()){ int id resultSet.getInt(1); String username resultSet.getString(2); int age resultSet.getInt(3); String password resultSet.getString(4); User user new User().setId(id).setUsername(username).setAge(age).setPassword(password); String roleName resultSet.getString(12); String roleDesc resultSet.getString(13); Role role new Role().setRoleName(roleName).setRoleDesc(roleDesc); String dname resultSet.getString(dname); Dept dept new Dept().setDname(dname); UserRoleDept userRoleDept new UserRoleDept().setUser(user).setRole(role).setDept(dept); list.add(userRoleDept); } return list; } catch (SQLException e) { throw new RuntimeException(e); }finally { DBUtil.release(connection,preparedStatement,resultSet); } }3.5 新增角色select * from menu; insert into role (role_name,role_desc) values(?,?) insert into role_menu(rid,mid) values(?,?)public class TestDemo { public static void main(String[] args) throws SQLException { MenuDao menuDao new MenuDaoImpl(); ListMenu menus menuDao.queryAll(); String str |- ; menus.stream() .filter(menu - menu.getParentMenuId() 0) .peek(parentMenu - { System.out.println(str parentMenu.getId() : parentMenu.getMenuName()); queryChildMenu(parentMenu,menus,| str); }) .count(); // 传统方法 // for (Menu menu : menus) { // if (menu.getParentMenuId() 0){ // System.out.println(|- menu.getId() menu.getMenuName()); // for (Menu menu1 : menus) { // if (menu1.getParentMenuId() menu.getId()){ // System.out.println(|- menu1.getId() menu1.getMenuName()); // for (Menu menu2 : menus) { // if (menu2.getParentMenuId() menu1.getId()){ // System.out.println(|- menu2.getId() menu2.getMenuName()); // } // } // } // } // } // } } /** * 层级展示菜单 * param parentMenu 父菜单 * param menuList 全部菜单 * param str 拼接的字符串 */ private static void queryChildMenu(Menu parentMenu,ListMenu menuList,String str){ menuList.stream().filter(menu - menu.getParentMenuId() parentMenu.getId()).peek(menu - { System.out.println(str menu.getId() : menu.getMenuName()); queryChildMenu(menu,menuList,| str); }).count(); } }RoleDao接口中public interface RoleDao { /** * 添加角色 * param role 角色对象 * return 生成的id */ int addRole(Role role) throws SQLException; int addRoleAndMenu(int rid,String[] mendIdArray) throws SQLException; } public class RoleDaoImpl implements RoleDao { Override public int addRole(Role role) throws SQLException { // 获取连接 Connection connection DBUtil.getConncetion(); // 执行sql String sql insert into role (role_name,role_desc) values(?,?); // 获取预编译对象 PreparedStatement preparedStatement connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS); // 给?赋值 preparedStatement.setString(1,role.getRoleName()); preparedStatement.setString(2,role.getRoleDesc()); // 执行sql preparedStatement.executeUpdate(); // 获取刚刚添加角色的id LAST_INSERT_ID() ResultSet resultSet preparedStatement.getGeneratedKeys(); int autoId 0; if (resultSet.next()){ autoId resultSet.getInt(1); } // 关闭连接 DBUtil.release(connection,preparedStatement); return autoId; } // insert into role_menu(rid,mid) values (?,?),(?,?),(?,?)... Override public int addRoleAndMenu(int rid, String[] mendIdArray) throws SQLException { // 获取连接 Connection connection DBUtil.getConncetion(); // 拼接sql StringBuilder stringBuilder new StringBuilder(); stringBuilder.append(insert into role_menu (rid,mid) values ); for (int i 0; i mendIdArray.length; i) { stringBuilder.append((?,?)); if (i mendIdArray.length - 1) break; stringBuilder.append(,); } // 获取预编译对象 PreparedStatement preparedStatement connection.prepareStatement(stringBuilder.toString()); // 给?赋值 int count 1; for (String menuId : mendIdArray) { preparedStatement.setObject(count,rid); preparedStatement.setObject(count,menuId); } // 执行sql语句 int row preparedStatement.executeUpdate(); // 关闭连接 DBUtil.release(connection,preparedStatement); return row; } }4 DCL事务是逻辑上的一组操作组成这组操作的单元要么同时成功要么同时失败4.1 Mysql进行事务管理create table account( id int PRIMARY KEY auto_increment, name VARCHAR(255), money double ) insert into account values (null,zs,1000); insert into account values (null,ls,1000); insert into account values (null,ww,1000); -- 开启事务 start transaction; -- 提交事务 commit; -- 回滚事务 rollback; update account set money money - 100 where name zs update account set money money 100 where name ls4.2 事务的特性和隔离级别【面试题】4.2.1 事务的特性原子性原子性是指事务是一个不可分割的工作单位。事务中的操作要么都发生要么都不发生一致性事务前后数据的完整性要保持一致zs 1000 ls 1000 总共2000 成功 zs 900 ls 1100 总共2000 不成功 zs 1000 ls 1000 总共2000持久性一个事务一旦提交对数据库中的数据改动是永久性的隔离性指多个用户并发操作数据库时一个用户的事务不能被其他用户的事务所干扰。4.2.2 没有隔离性会引发的问题可能出现的问题含义脏读一个事务读取到了另一个事务中尚未提交的数据不可重复读一个事务中两次读取到的数据内容不一致幻读一个事务中两次读取到的数据的数量不一致4.2.3 事务的隔离级别级别名字隔离级别脏读不可重复读幻读数据库的默认级别1读未提交read uncommitted是是是2读已提交read committed否是是oracle3可重复读repeatable read否否是mysql4串行化serializable否否否隔离级别越高安全性越高性能效率越差-- 查看当前事务的隔离级别 select transaction_isolation; -- 设置当前事务的隔离级别 set session transaction isolation level 隔离级别4.3 代码级别使用事务// 开启事务 connection.setAutoCommit(false); // 提交事务 connection.commit(); // 回滚事务 connection.rollback();package cn.javasm.service.impl; import cn.javasm.dao.RoleDao; import cn.javasm.dao.impl.RoleDaoImpl; import cn.javasm.entity.Role; import cn.javasm.service.RoleService; import cn.javasm.utils.DBUtil; import java.sql.Connection; import java.sql.SQLException; /** * author : gfs * version : 0.1 * className: RoleServiceImpl * date : 2025/12/10 11:00 * description: * since : jdk17 */ public class RoleServiceImpl implements RoleService { Override public int insertRoleService(Role role, String[] menuIdArray) { // 业务逻辑层 密码加密 事务控制 记录日志 检查权限... // 获取连接 Connection connection DBUtil.getConncetion(); int row 0; try { // 手动开启事务 connection.setAutoCommit(false); RoleDao roleDao new RoleDaoImpl(connection); int roleId roleDao.addRole(role); // int i 1 / 0; row roleDao.addRoleAndMenu(roleId, menuIdArray); // 提交事务 connection.commit(); } catch (Exception e) { try { // 回滚事务 connection.rollback(); } catch (SQLException ex) { throw new RuntimeException(ex); } throw new RuntimeException(e); }finally { // 关闭连接 DBUtil.release(connection); } return row; } }5 自定义连接池5.1 初级版本package cn.javasm.utils; import java.sql.Connection; import java.util.LinkedList; /** * author : gfs * version : 0.1 * className: MyDataSource1 * date : 2025/12/10 11:30 * description: * since : jdk17 */ public class MyDataSource1 { private static LinkedListConnection pool; static { pool new LinkedList(); for (int i 0; i 5; i) { pool.add(DBUtil.getConncetion()); } } /** * 获取连接 * return */ public Connection getConnection(){ Connection connection pool.removeFirst(); return connection; } /** * 归还 */ public void addBack(Connection connection){ pool.addLast(connection); } }5.2 进阶版本所有的厂商都要实现sun公司提供的连接池接口package cn.javasm.utils; import javax.sql.DataSource; import java.io.PrintWriter; import java.sql.Connection; import java.sql.SQLException; import java.sql.SQLFeatureNotSupportedException; import java.util.LinkedList; import java.util.logging.Logger; /** * author : gfs * version : 0.1 * className: MyDataSource2 * date : 2025/12/10 11:35 * description: * since : jdk17 */ public class MyDataSource2 implements DataSource { private static LinkedListConnection pool; static { pool new LinkedList(); for (int i 0; i 5; i) { pool.add(DBUtil.getConncetion()); } } Override public Connection getConnection() throws SQLException { return pool.removeFirst(); } public void addBack(Connection connection){ pool.addLast(connection); } Override public Connection getConnection(String username, String password) throws SQLException { return null; } Override public PrintWriter getLogWriter() throws SQLException { return null; } Override public void setLogWriter(PrintWriter out) throws SQLException { } Override public void setLoginTimeout(int seconds) throws SQLException { } Override public int getLoginTimeout() throws SQLException { return 0; } Override public Logger getParentLogger() throws SQLFeatureNotSupportedException { return null; } Override public T T unwrap(ClassT iface) throws SQLException { return null; } Override public boolean isWrapperFor(Class? iface) throws SQLException { return false; } }5.3 最终版本装饰设计模式:是23种常用的面向对象软件设计模式之一。动态的将责任附件到对象上要想扩展功能装饰者提供了比继承更加有弹性的替代方案。使用的条件:增强类和被增强类实现同一个接口或者有共同的父类增强类中要拿到被增强类的引用public class TestDemo2 { public static void main(String[] args) { Car car new Benz(new Mzd()); car.run(); car.stop(); } } interface Car{ void run(); void stop(); } // 被增强类 class Mzd implements Car{ Override public void run() { System.out.println(跑的慢塞车); } Override public void stop() { System.out.println(skr~); } } // 增强类 class Benz implements Car{ private Car car; public Benz(Car car) { this.car car; } Override public void run() { System.out.println(3s破百); } Override public void stop() { car.stop(); } }public class MyConnection implements Connection { private Connection connection; private LinkedListConnection pool; public MyConnection(Connection connection, LinkedListConnection pool) { this.connection connection; this.pool pool; } Override public void close() throws SQLException { pool.addLast(connection); System.out.println(归还了连接 connection); } Override public PreparedStatement prepareStatement(String sql) throws SQLException { return connection.prepareStatement(sql); } Override public void setAutoCommit(boolean autoCommit) throws SQLException { connection.setAutoCommit(autoCommit); } Override public void commit() throws SQLException { connection.commit(); } Override public void rollback() throws SQLException { connection.rollback(); } Override public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException { return connection.prepareStatement(sql,autoGeneratedKeys); } public class MyDataSource3 implements DataSource { private static LinkedListConnection pool; static { pool new LinkedList(); for (int i 0; i 5; i) { pool.add(DBUtil.getConncetion()); } } Override public Connection getConnection() throws SQLException { Connection connection pool.removeFirst(); System.out.println(获取了连接 connection); MyConnection myConnection new MyConnection(connection,pool); return myConnection; }6 MD5加密JDK中实现加密 BASE64(可逆的) public static void main(String[] args) { Base64.Encoder encoder Base64.getEncoder(); String str encoder.encodeToString(1234.getBytes()); System.out.println(str); Base64.Decoder decoder Base64.getDecoder(); byte[] decode decoder.decode(str); System.out.println(new String(decode)); } MD5加密 public class MD5Util { private MD5Util(){} private static final String SALT eeg54yhrtg; public static String encode(String str) throws NoSuchAlgorithmException { // 获取MD5对象 MessageDigest messageDigest MessageDigest.getInstance(MD5); str SALT; messageDigest.update(str.getBytes()); byte[] bytes messageDigest.digest(); BigInteger bigInteger new BigInteger(1,bytes); String string bigInteger.toString(16); System.out.println(string); return new String(bytes); } }