JDBC 建立连接公共操作类（静态方式与单例方式）
静态方式package com.ighost.jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;/** * * 数据库操作公共类 * * @author ghost * */public final class JDBCUtil { private static String url = "jdbc:mysql://localhost:3306/jdbc"; private static String username = "root"; private static String password = ""; // 构造函数私有话 不允许构造 private JDBCUtil() { } // 注册驱动 static { try { Class.forName("com.mysql.jdbc.Driver"); } catch (ClassNotFoundException e) { throw new ExceptionInInitializerError(e); } } // 获取连接 public static Connection getConnection() throws SQLException { return DriverManager.getConnection(url, username, password); } // 释放资源 public static void free(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(); } } } }}单例方式package com.ighost.jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;/** * * 数据库操作公共类 单例模式 虚拟机里只存在一个这样的实例 通过getInstance方式获取对象 * * @author ghost * */public final class JDBCUtilSingle { private String url = "jdbc:mysql://localhost:3306/jdbc"; private String username = "root"; private String password = ""; // 构造函数私有话 不允许构造 private JDBCUtilSingle() { } // 构造私有实例 // private static JDBCUtilSingle instance = new JDBCUtilSingle(); private static JDBCUtilSingle instance = null; public static JDBCUtilSingle getInstance() { //延迟加载 if (instance == null) { //加锁 防止线程并发 synchronized (JDBCUtilSingle.class) { //必须有的判断 if(instance == null){ instance = new JDBCUtilSingle(); } } } return instance; } // 注册驱动 static { try { Class.forName("com.mysql.jdbc.Driver"); } catch (ClassNotFoundException e) { throw new ExceptionInInitializerError(e); } } // 获取连接 public Connection getConnection() throws SQLException { return DriverManager.getConnection(instance.url, instance.username, instance.password); } // 释放资源 public static void free(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(); } } } }}?