2：Jdbc工具类

工具类

public final class JdbcUtil {/*** 连接字符串*/private static final String URL = "jdbc:mysql://localhost:3306/db_test?useSSL=false&serverTimezone=GMT%2B8&characterEncoding=utf8&useUnicode=true";/*** 用户名*/private static final String USERNAME = "root";/*** 密码*/private static final String PASSWORD = "root";/*** 驱动类名*/private static final String DRIVER = "com.mysql.cj.jdbc.Driver";static {try {// 1、加载驱动Class.forName(DRIVER);} catch (ClassNotFoundException e) {throw new ExceptionInInitializerError(e);}}public static Connection getConnection() throws SQLException {return DriverManager.getConnection(URL, USERNAME, PASSWORD);}public static void release(ResultSet rs, Statement stmt, Connection conn) {// 建议采用这种形式来释放资源，因为finally里面的一定会被释放try {if (rs != null) {rs.close();}} catch (SQLException e) {e.printStackTrace();} finally {try {if (stmt != null) {stmt.close();}} catch (SQLException e) {e.printStackTrace();} finally {if (conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}}}
}

测试代码

public final class JdbcUtilTest {private static void selectAllDepts(String sql) {try {// 2、建立连接Connection conn = JdbcUtil.getConnection();// 3、获取Statement对象Statement stmt = conn.createStatement();// 执行SQL语句ResultSet rs = stmt.executeQuery(sql);// 处理返回的结果while (rs.next()) {System.out.println(rs.getInt(1) + "  " + rs.getString("dname") + "  "+ rs.getString("loc"));}// 释放资源JdbcUtil.release(rs, stmt, conn);} catch (SQLException e) {e.printStackTrace();}}public static void main(String[] args) {String sql = "SELECT * FROM tb_dept";selectAllDepts(sql);}
}

代码优化

将数据库的连接信息写到属性配置文件中

• 属性配置文件：mysql.properties

  url=jdbc:mysql://localhost:3306/test?useSSL=false&serverTimezone=GMT%2B8&characterEncoding=utf8&useUnicode=true
  user=root
  password=root
  

• 工具类

public class JdbcUtil {private static String url;private static String user;private static String password;static {//Map的實現類Properties properties = new Properties();// 重点InputStream rss = JdbcUtil.class.getResourceAsStream("/mysql.properties");try {//加載驅動（Java項目可以不要改句，web項目必須）Class.forName("com.mysql.jdbc.Driver");//加載properties文件properties.load(rss);} catch (IOException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();}url = properties.getProperty("url");System.out.println(url);user = properties.getProperty("user");password = properties.getProperty("password");}public static Connection getConnection() throws SQLException {Connection conn = DriverManager.getConnection(url, user, password);return conn;}public static void release(ResultSet rs, Statement stmt, Connection conn) {try {if (rs != null) {rs.close();}} catch (SQLException e) {e.printStackTrace();} finally {try {if (stmt != null) {stmt.close();}} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}}}
}

进阶

为了提高程序的性能，建议采用数据库连接池技术，请参看博客：数据库连接池技术

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