实现用户登录系统的前后端开发实验一

package com.example.webdemo.util; import java.io.IOException; import java.io.InputStream; import java.sql.*; import java.util.Properties; import java.util.logging.Level; import java.util.logging.Logger; /** * 数据库连接与操作工具类。 */ public class DBUtil { private static String driver; private static String url; private static String username; private static String password; private static Connection conn = null; private static PreparedStatement pst = null; private static ResultSet rs = null; static { try { //静态代码快，在类加载的时候执行 init(); } catch (Exception ex) { Logger.getLogger(DBUtil.class.getName()).log(Level.SEVERE, null, ex); } } /** * 初始化连接参数，从配置文件里获得 * * @throws IOException */ public static void init() throws Exception { Properties params = new Properties(); String configFile = "com/example/webdemo/database.properties"; //加载配置文件到输入流中 InputStream is = DBUtil.class.getClassLoader().getResourceAsStream(configFile); //从输入流中读取属性列表 params.load(is); //根据指定的获取对应的值 driver = params.getProperty("driver"); url = params.getProperty("url"); username = params.getProperty("username"); password = params.getProperty("password"); Class.forName(driver); } /** * 获取数据库连接对象 * * @return * @throws ClassNotFoundException * @throws SQLException */ public static void getConnection() throws Exception { conn = DriverManager.getConnection(url, username, password); } /** * 执行SQL语句，可以进行查询 */ public static ResultSet executeQuery(String preparedSql, Object... param) throws Exception { getConnection(); pst = conn.prepareStatement(preparedSql); if (param != null) { for (int i = 0; i < param.length; i++) { //为预编译sql设置参数 pst.setObject(i + 1, param[i]); } } rs = pst.executeQuery(); return rs; } /** * 执行SQL语句，可以进行增、删、改的操作，不能执行查询 */ public static int executeUpdate(String preparedSql, Object... param) throws Exception { int num; getConnection(); try (Connection connection = conn; PreparedStatement pstmt = connection.prepareStatement(preparedSql)) { if (param != null) { for (int i = 0; i < param.length; i++) { pstmt.setObject(i + 1, param[i]);//为预编译sql设置参数 } } num = pstmt.executeUpdate(); return num; } } public static void closeAll() throws Exception { //如果rs不空，关闭rs if (rs != null) { rs.close(); } //如果pstmt不空，关闭pstmt if (pst != null) { pst.close(); } //如果conn不空，关闭conn if (conn != null) { conn.close(); } } }