1 import java.sql.Connection;  2 import java.sql.DriverManager;  3 import java.sql.PreparedStatement;  4 import java.sql.ResultSet;  5 import java.sql.Statement;  6   7 /**  8  * 数据库工具类，负责完成打开、关闭数据库，执行查询或更新  9  * @author MKing 10  * 11  */ 12 public class DbHelper { 13     /** 14      * 数据库URL 15      */ 16     private static final String URL = "jdbc:mysql://localhost:3306/bookstore"; 17     /** 18      * 登录用户名 19      */ 20     private static final String USER = "root"; 21     /** 22      * 登录密码 23      */ 24     private static final String PASSWORD = "12345"; 25      26     private static Connection connection = null; 27     private static Statement statement = null; 28  29     private static DbHelper helper = null; 30  31     static { 32         try { 33             Class.forName("com.mysql.jdbc.Driver"); 34         } catch (ClassNotFoundException e) { 35             e.printStackTrace(); 36         } 37     } 38  39     private DbHelper() throws Exception { 40         connection = DriverManager.getConnection(URL, USER, PASSWORD); 41         statement = connection.createStatement(); 42     } 43  44     /** 45      * 返回单例模式的数据库辅助对象 46      *  47      * @return 48      * @throws Exception  49      */ 50     public static DbHelper getDbHelper() throws Exception { 51         if (helper == null || connection == null || connection.isClosed()) 52             helper = new DbHelper(); 53         return helper; 54     } 55  56     /** 57      * 执行查询 58      * @param sql 要执行的SQL语句 59      * @return  查询的结果集对象 60      * @throws Exception 61      */ 62     public ResultSet executeQuery(String sql) throws Exception { 63         if (statement != null) { 64             return statement.executeQuery(sql); 65         } 66  67         throw new Exception("数据库未正常连接"); 68     } 69  70     /** 71      * 执行查询 72      * @param sql  要执行的带参数的SQL语句 73      * @param args  SQL语句中的参数值 74      * @return  查询的结果集对象 75      * @throws Exception 76      */ 77     public ResultSet executeQuery(String sql, Object...args) throws Exception { 78         if (connection == null || connection.isClosed()) { 79             DbHelper.close(); 80             throw new Exception("数据库未正常连接"); 81         } 82         PreparedStatement ps = connection.prepareStatement(sql); 83         int index = 1; 84         for (Object arg : args) { 85             ps.setObject(index, arg); 86             index++; 87         } 88          89         return ps.executeQuery(); 90     } 91      92     /** 93      * 执行更新 94      * @param sql  要执行的SQL语句 95      * @return  受影响的记录条数 96      * @throws Exception 97      */ 98     public int executeUpdate(String sql) throws Exception { 99         if (statement != null) {100             return statement.executeUpdate(sql);101         }102         throw new Exception("数据库未正常连接");103     }104     105     /**106      * 执行更新107      * @param sql  要执行的SQL语句108      * @param args  SQL语句中的参数109      * @return  受影响的记录条数110      * @throws Exception111      */112     public int executeUpdate(String sql, Object...args) throws Exception {113         if (connection == null || connection.isClosed()) {114             DbHelper.close();115             throw new Exception("数据库未正常连接");116         }117         PreparedStatement ps = connection.prepareStatement(sql);118         int index = 1;119         for (Object arg : args) {120             ps.setObject(index, arg);121             index++;122         }123         return ps.executeUpdate();124     }125     126     /**127      * 获取预编译的语句对象128      * @param sql  预编译的语句129      * @return  预编译的语句对象130      * @throws Exception131      */132     public PreparedStatement prepareStatement(String sql) throws Exception {133         return connection.prepareStatement(sql);134     }135     136     /**137      * 关闭对象，同时将关闭连接138      */139     public static void close() {140         try {141             if (statement != null)142                 statement.close();143             if (connection != null) 144                 connection.close();145         } catch (Exception e) {146             e.printStackTrace();147         } finally {148             helper = null;149         }150     }151 }