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在dao下新建BaseDao类用于读取上面的数据库配置文件

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import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;
//操作数据库的公共类
     public class BaseDao {     
         private static String driver;
         private static String url;
         private static String username;
         private static String password;
     
         //静态代码块，类加载的时候就初始化了
         static {
             Properties properties = new Properties();
             //通过类加载器读取对应的资源
             InputStream is = BaseDao.class.getClassLoader().getResourceAsStream("db.properties");
     
             try {
                 properties.load(is);
             } catch (IOException e) {
                 e.printStackTrace();
             }
     
             driver = properties.getProperty("driver");
             url = properties.getProperty("url");
             username = properties.getProperty("username");
             password = properties.getProperty("password");
         }
     
         //获取数据库的链接
         public static Connection getConnection(){
             Connection connection = null;
             try {
                 Class.forName(driver);
                 connection = DriverManager.getConnection(url, username, password);
             } catch (Exception e) {
                 e.printStackTrace();
             }
             return connection;
         }
     
         //编写查询公共方法
         public static ResultSet execute(Connection connection,String sql,Object[] params,ResultSet resultSet,PreparedStatement preparedStatement) throws SQLException {
             //预编译的sql，在后面直接执行就可以了
             preparedStatement = connection.prepareStatement(sql);
     
             for (int i = 0; i < params.length; i++) {
                 //setObject,占位符从1开始，但是我们的数组是从0开始！
                 preparedStatement.setObject(i+1,params[i]);
             }
     
             resultSet = preparedStatement.executeQuery();
             return resultSet;
         }
     
     
         //编写增删改公共方法
         public static int execute(Connection connection,String sql,Object[] params,PreparedStatement preparedStatement) throws SQLException {
             preparedStatement = connection.prepareStatement(sql);
     
             for (int i = 0; i < params.length; i++) {
                 //setObject,占位符从1开始，但是我们的数组是从0开始！
                 preparedStatement.setObject(i+1,params[i]);
             }
     
             int updateRows = preparedStatement.executeUpdate();
             return updateRows;
         }
     
     
         //释放资源
         public static boolean closeResource(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet){
             boolean flag = true;
     
             if (resultSet!=null){
                 try {
                     resultSet.close();
                     //GC回收
                     resultSet = null;
                 } catch (SQLException e) {
                     e.printStackTrace();
                     flag = false;
                 }
             }
     
             if (preparedStatement!=null){
                 try {
                     preparedStatement.close();
                     //GC回收
                     preparedStatement = null;
                 } catch (SQLException e) {
                     e.printStackTrace();
                     flag = false;
                 }
             }
     
             if (connection!=null){
                 try {
                     connection.close();
                     //GC回收
                     connection = null;
                 } catch (SQLException e) {
                     e.printStackTrace();
                     flag = false;
                 }
             }
             return flag;
         }
     }

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