private void login() throws SQLException { try { Class.forName("com.mysql.jdbc.Driver"); } catch (ClassNotFoundException e) { System.out.println("ForName:" + e.getMessage()); } Connection Ex1Con = DriverManager.getConnection("jdbc:mysql://localhost:3306/testdb" + "?useUnicode=true&characterEncoding=utf8", "root", "123456"); Statement Ex1Stem = Ex1Con.createStatement(); String username, password, phone; ResultSet rs = Ex1Stem.executeQuery("select * from user"); username = rs.getString("username"); password = rs.getString("password"); phone = rs.getString("phone"); if (username.equals(t1.getText()) && password.equals(t2.getText()) && phone.equals(t3.getText())) { JOptionPane.showMessageDialog(this, "登录成功"); } else { JOptionPane.showMessageDialog(this, "信息不对"); } }该段代码的作用并逐行进行翻译和解释

private String driver = "com.mysql.jdbc.Driver"; private String url = "jdbc:mysql://localhost:3306/rents?useUnicode=true&characterEncoding=utf-8"; private String user = "root"; private String password = "root"; public Connection getConnection() throws SQLException { try { Class.forName(driver); } catch (java.lang.ClassNotFoundException cnfe) { cnfe.printStackTrace(); } Connection conn = null; //conn=DriverManager.getConnection(URL, "root", "12481632"); try { conn = DriverManager.getConnection(url, user, password); }catch(SQLException ex) { ex.printStackTrace(); } return conn; } /*

在这个方法中，首先使用Class.forName()方法加载MySQL的JDBC驱动程序，然后使用DriverManager.getConnection()方法建立与MySQL数据库的连接。如果连接过程中出现异常，getConnection()方法将抛出SQLException异常并...

private void 点击注册() throws SQLException{ try { Class.forName("com.mysql.jdbc.Driver"); }catch(ClassNotFoundException e) { System.out.println("ForName:"+e.getMessage()); } Connection Ex1Con = DriverManager.getConnection("jdbc:mysql://localhost:3306/TestDB?useSSL=false","root","123456"); Statement Ex1Stem = Ex1Con.createStatement(); Ex1Stem.executeUpdate("creat table if not exists user(username char(8),password char(16),"); Ex1Stem.execute("insert into user(username,password)values('"+t1.getText()+"','"+t2.getText()+"','"+"')"); Ex1Stem.close(); JOptionPane.showMessageDialog(this,"用户注册成功"); } }详细的逐行解释该段代码

Class.forName("com.mysql.jdbc.Driver"); } catch(ClassNotFoundException e) { System.out.println("ForName:"+e.getMessage()); } // 使用 Class.forName() 方法加载 MySQL 数据库的 JDBC 驱动程序。 3. ...

public void testJdbc() throws ClassNotFoundException, SQLException { Class.forName("com.mysql.cj.jdbc.Driver"); Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/javawebdb?serverTimezone=UTC", "root", "wwd20020906"); PreparedStatement preparedStatement = connection.prepareStatement("select * from t_user"); ResultSet resultSet = preparedStatement.executeQuery(); while (resultSet.next()) { System.out.println("id:" + resultSet.getString("id") + ",name:" + resultSet.getString("name") + ",age:" + resultSet.getString("age")); } resultSet.close(); preparedStatement.close(); connection.close(); }

这是一个使用Java JDBC连接MySQL数据库的测试方法。该方法首先加载MySQL驱动程序，然后通过驱动程序管理器获取数据库连接。接下来，它创建一个预处理语句，并执行一个查询语句来检索用户表中的数据。然后，使用结果...

详细注释代码 public void del_cource (String id) throws SQLException, ClassNotFoundException { Class.forName("com.mysql.jdbc.Driver"); Connection connection = DriverManager.getConnection("jdbc:mysql://" + host + ":3306/db_stu_score", "root", ""); String sql = "DELETE from tb_cource where id = ?; "; PreparedStatement statement = connection.prepareStatement(sql); statement.setString(1, id); statement.executeUpdate(); statement.close(); connection.close(); }

Class.forName("com.mysql.jdbc.Driver"); // 连接到数据库 Connection connection = DriverManager.getConnection("jdbc:mysql://" + host + ":3306/db_stu_score", "root", ""); // SQL语句，用于删除指定id的...

public ClubManagementSystem() throws ClassNotFoundException { try { Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD); } catch (SQLException e) { e.printStackTrace(); }

这段 Java 代码是一个俱乐部管理系统的构造函数。它的作用是连接到一个 Microsoft...它首先尝试加载 Microsoft SQL Server 的 JDBC 驱动程序，如果加载成功，就会尝试连接到数据库。如果连接失败，就会打印出错误信息。

添加代码使得这段代码显示在一个窗口中：package csclient; import java.sql.*; public class Test { private static String driver = "com.mysql.cj.jdbc.Driver"; private static String URL = "jdbc:mysql://localhost:3306/student"; private static String user = "root"; private static String password = "z7.h7.m7."; /** * JDBC测试. */ private static void JDBCexample() { // 1.加载数据库驱动 try { Class.forName(driver); } catch (ClassNotFoundException e) { e.printStackTrace(); } testStatement(); } /** * 测试Statement的用法. */ private static void testStatement() { try (// 2.打开数据库连接 Connection conn = DriverManager.getConnection(URL, user, password); // 3.创建语句 Statement stmt = conn.createStatement()) { // 模拟SQL注入 testSqlInjecton(stmt); } catch (SQLException sqle) { System.out.println("SQLException : " + sqle); } } /** * 模拟SQL注入. * * @param stmt Statement对象. * @throws SQLException / private static void testSqlInjecton(Statement stmt) throws SQLException { String name = "X' or 'Y' = 'Y"; String sql = "select from stu_info where name = '" + name + "'"; ResultSet rs = stmt.executeQuery(sql); ResultSetPrinter.printResultSet(rs); } public static void main(String[] args) { JDBCexample(); } }

加载数据库驱动 try { Class.forName(driver); } catch (ClassNotFoundException e) { e.printStackTrace(); } testStatement(); } /** * 测试Statement的用法. */ private static void testStatement() { try (// 2...

帮我优化这段代码，谢谢package com.neutech.utils; import java.sql.*; import java.util.ArrayList; import java.util.List; public class Jdbcutil { private static final String DRIVERNAME = "org.apache.hive.jdbc.HiveDriver"; private static final String URL = "jdbc:hive2://192.168.44.199:10000/test"; private static final String USERNAME = "root"; private static final String PASSWORD = "200812"; public static Connection getConnection() throws ClassNotFoundException { Class.forName(DRIVERNAME); Connection connection = null; try { connection = DriverManager.getConnection(URL,USERNAME,PASSWORD); } catch (SQLException throwables) { throwables.printStackTrace(); } return connection; } public static <T> List<T> execuetQuery(String sql, RowMap<T> rowMap, Object... objs) throws ClassNotFoundException, SQLException { // 建立连接 Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(sql); // 注入额外条件 if(objs != null){ for(int i = 0;i <= objs.length;i++){ preparedStatement.setObject(i + 1,objs[i]); } } ResultSet resultSet = preparedStatement.executeQuery(); ArrayList<T> list = new ArrayList<>(); while(resultSet.next()){ T t = rowMap.RowMapping(resultSet); list.add(t); } return list; } public static void close(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet) throws SQLException { connection.close(); preparedStatement.close(); resultSet.close(); } }

Class.forName(driverName); } catch (Exception e) { throw new RuntimeException("Failed to initialize JdbcUtil.", e); } } public static Connection getConnection() throws SQLException { return ...

帮我解释一下public static Map<String, Object> getFriendDataFromDB(int id) throws ClassNotFoundException { Class.forName("com.mysql.jdbc.Driver"); Map<String, Object> friendData = null; try { Connection conn = DriverManager.getConnection(url, user, password); Statement stmt = conn.createStatement(); System.out.println("数据库连接成功2"); String sql = "SELECT ri.name, ri.sign, ri.nickname FROM registrationinformation ri JOIN mytabulation mt ON ri.id = mt.taid WHERE mt.myid = " + id + " LIMIT 1"; ResultSet rs = stmt.executeQuery(sql); System.out.println("数据库执行成功"); if (rs.next()) { friendData = new HashMap<>(); friendData.put("name", rs.getString("name")); friendData.put("sign", rs.getString("sign")); friendData.put("nickname", rs.getString("nickname")); } rs.close(); stmt.close(); conn.close(); } catch (SQLException e) { e.printStackTrace(); } return friendData; }

这是一个 Java 方法，它从...该方法使用了 JDBC API 连接到 MySQL 数据库，并执行了一个 SQL 查询语句。如果查询成功，它会将查询结果存储在一个 HashMap 对象中，并返回该对象。如果查询失败，它会打印出异常信息。

package com.visual.utils; import java.sql.; import java.util.List; public class DBBean { private String url = "jdbc:mysql://47.101.187.125:3310/douban?useSSL=false"; // 数据库信息，旧版本中不用useSSL=false private String username = "root"; private String password = "rootRoot123."; private String driverName = "com.mysql.jdbc.Driver"; private Connection con = null; //连接对象 private PreparedStatement pstmt = null; //语句对象 private ResultSet rs = null; //结果集对象 public DBBean() throws ClassNotFoundException, SQLException { Class.forName(driverName); con = DriverManager.getConnection(url, username, password); } / * sql:要执行的SQL语句 * params：SQL语句中需要的变量 */ public int executeUpdate(String sql, List<Object> params) throws SQLException { pstmt = con.prepareStatement(sql); if (params != null && params.size() > 0) { for (int i = 0; i < params.size(); i++) { pstmt.setObject(i + 1, params.get(i)); } } return pstmt.executeUpdate(); } public ResultSet executeQuery(String sql, List<Object> params) throws SQLException { pstmt = con.prepareStatement(sql); if (params != null && params.size() > 0) { for (int i = 0; i < params.size(); i++) { pstmt.setObject(i + 1, params.get(i)); } } return pstmt.executeQuery(); } public void close() { if (rs != null) { try { rs.close(); } catch (Exception ee) { } } if (pstmt != null) { try { pstmt.close(); } catch (Exception ee) { } } if (con != null) { try { con.close(); } catch (Exception ee) { } } } }

它使用JDBC连接到MySQL数据库，并提供了执行SQL语句的方法。该类包含以下属性： - url：数据库的URL地址 - username：数据库用户名 - password：数据库密码 - driverName：MySQL驱动程序的类名该类有一个构造...

解析一下以下代码以及可能出现的错误public String borrow_query01(String bid,String id) throws Exception { Connection conn = null; // 更新数据库连接信息 Class.forName("com.mysql.cj.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/bookmanag

在这里，使用了 MySQL 提供的 JDBC 驱动，Class.forName() 方法用于加载该驱动。接下来，声明了数据库的 URL，包括数据库地址、端口号和数据库名称等信息。在方法主体中，该方法使用了 PreparedStatement 对象，...

public class dbConn { public dbConn() { try { jbInit(); } catch (Exception e) { e.printStackTrace(); } } private Statement conn() { try { // 加载驱动 Class.forName("com.mysql.jdbc.Driver"); // 数据库名称，管理员账号、密码 String url = "jdbc:mysql://localhost:3306/test"; String user = "root"; String pwd = "123456789"; // 连接 Connection con = null; con = DriverManager.getConnection(url, user, pwd); Statement stat = con.createStatement(); return stat; } catch (ClassNotFoundException ex) { return null; } catch (SQLException ex1) { return null; } } // 查询数据库 public ResultSet getRs(String sql) { try { Statement stat = conn(); ResultSet rs = stat.executeQuery(sql); System.out.println(rs); return rs; } catch (SQLException ex) { System.err.println("------------" + ex.getMessage()); return null; } } // 更新数据库 public int getUpdate(String sql) { try { Statement stat = conn(); int i = stat.executeUpdate(sql); return i; } catch (Exception ex) { System.out.println(">>>>>>>>" + ex.getMessage()); return -1; } } private void jbInit() throws Exception { conn(); } }代码报错java.lang.NullPointerException: Cannot invoke "java.sql.Statement.executeQuery(String)" because "stat" is null

这个错误是因为在执行查询语句时，可能出现了连接数据库失败的情况，导致 conn() 函数返回了 null，所以在 getRs(String sql) 函数中执行 stat.executeQuery(sql) 时，会抛出 NullPointerException 异常。...

import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; public class Login { Admin admin; void setAdmin(Admin admin) { this.admin=admin; //System.out.println(this.admin.getPassword()+" " + this.admin.getID()); } /* * JudgeAdmin()方法 * 判断User的ID和密码是否正确，如果正确，显示登录成功 * 如果错误，弹出一个窗口，显示账号或密码错误 / private String driver = "com.mysql.jdbc.Driver"; private String url = "jdbc:mysql://localhost:3306/qqq?serverTimezone=UTC&characterEncoding=utf-8"; private String user = "root"; private String password = "root"; public boolean login(Admin admin) throws SQLException, ClassNotFoundException { String sql="select from admin where id=? and password=?"; Class.forName(driver); Connection conn = DriverManager.getConnection(url, user, password); PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, admin.getID()); ps.setString(2, admin.getPassword()); ResultSet rs = ps.executeQuery(); int ans = 0; if(rs.next()) { ans = 1; } rs.close(); ps.close(); conn.close(); if(ans == 1) { return true; } else return false; } int JudgeAdmin() { try { if(login(this.admin)) { System.out.println("登录成功"); return 1; }else { return 0; } }catch(Exception e) { //e.printStackTrace(); //System.out.println("!!!!!!!!!"); } return 0; } }

在 login 方法中，使用了 JDBC 连接数据库，执行了一次 SQL 查询语句，根据查询结果返回 true 或 false。在 JudgeAdmin 方法中，调用了 login 方法，如果返回 true，则打印出登录成功的信息并返回 1，否则返回 0。

public void druglibUpdateFor20230530() throws UpdateException { Connection conn = null; Statement stmt = null; try { final String jdbcDriver = "com.mysql.cj.jdbc.Driver"; Class.forName(jdbcDriver); //硬编码连接数据库 conn = DriverManager.getConnection(DB_URL + "/" + DatabaseEnum.D_DRUG_LIB.getName() + "?useSSL=false", USER, PASS); conn.setAutoCommit(false); stmt = conn.createStatement(); //迁移t_data_set表数据到common_be库 String dataSetTransfer = "insert " + DatabaseEnum.COMMON_BE.getName() + ".t_data_set select * from " + DatabaseEnum.D_DRUG_LIB.getName() + ".t_data_set"; String treatmentTransfer = "insert " + DatabaseEnum.COMMON_BE.getName() + ".t_treatment select * from " + DatabaseEnum.D_DRUG_LIB.getName() + ".t_treatment"; String dropDrugLib = "drop database " + DatabaseEnum.D_DRUG_LIB.getName(); stmt.executeUpdate(dataSetTransfer); if (Boolean.TRUE.equals(judgeTableExists("t_treatment", stmt))) { stmt.executeUpdate(treatmentTransfer); } stmt.executeUpdate(dropDrugLib); log.info("一体化drug_lib库数据迁移完成"); } catch (ClassNotFoundException | SQLException e) { if (null != conn) { try { conn.rollback(); } catch (SQLException ex) { throw new UpdateException(ex.getMessage()); } } e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.close(conn, stmt); } }

Class.forName(jdbcDriver); conn.setAutoCommit(false); stmt.executeUpdate(dataSetTransfer); if (Boolean.TRUE.equals(judgeTableExists("t_treatment", stmt))) { stmt.executeUpdate(treatmentTransfer)...

package com.util; import java.sql.Connection; import java.util.Random; import java.sql.*; import com.util.SQLConn; public class RandomStringGenerator { public RandomStringGenerator() throws SQLException{ // 构造函数中调用可能会抛出SQLException异常的方法 // 添加异常处理语句 try{ final String UPDATE_SQL = "INSERT INTO strings (value) VALUES (?)"; try { Connection conn = SQLConn.openDB(); Class.forName("com.sqlserver.jdbc.Driver"); // 生成随机字符串 Random rand = new Random(); StringBuilder sb = new StringBuilder(); for (int i = 0; i < 5; i++) { char c = (char) (rand.nextInt(26) + 'a'); sb.append(c); } String str = sb.toString(); // 保存到数据库 PreparedStatement pstmte = conn.prepareStatement(UPDATE_SQL); { pstmte.setInt(1, 1); pstmte.executeUpdate(); } System.out.println("随机字符串已保存到数据库中：" + str); pstmte.close(); conn.close(); } catch (ClassNotFoundException e) { e.printStackTrace(); } }catch(SQLException e){ // exception handling here throw e; } }优化代码

下面是对代码的一些优化： 1. 删除了不必要的 try-catch 语句，因为异常应该在最外层进行处理，不需要在方法内部处理。... } catch (SQLException e) { // exception handling here throw e; } } }

在IDEA中使用Java进行MySQL数据库操作及驱动配置

- 加载MySQL驱动：使用Class.forName("com.mysql.cj.jdbc.Driver")这行代码加载MySQL JDBC驱动。 - 建立连接：通过DriverManager.getConnection()方法使用数据库的URL、用户名和密码建立连接。 - 创建Statement...

JDBC数据库连接模板：Java数据库编程实践

Class.forName("com.mysql.cj.jdbc.Driver"); return DriverManager.getConnection(URL, USER, PASSWORD); } public static void close(Connection conn, Statement stmt, ResultSet rs) { try { if (rs != ...

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public ClubManagementSystem() throws ClassNotFoundException { try { Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD); } catch (SQLException e) { e.printStackTrace(); }

解析一下以下代码以及可能出现的错误public String borrow_query01(String bid,String id) throws Exception { Connection conn = null; // 更新数据库连接信息 Class.forName("com.mysql.cj.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/bookmanag

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