封装BaseDao

package tool;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.*;

public class BaseDao {
   static private String user = "root";
   static private String pwd = "root";
   static String classname = "com.mysql.jdbc.Driver";
   static String url = "jdbc:mysql://localhost:3306/exam?characterEncoding=utf8";
   static {
       try {
           Class.forName(classname);
       } catch (ClassNotFoundException e) {
           e.printStackTrace();
       }
   }

   public static Connection getcon() throws SQLException {
       return DriverManager.getConnection(url, user, pwd);
   }

   public static void close(Connection con, Statement pre, ResultSet re) {
       try {
           if (con != null)
               con.close();
           if (pre != null)
               pre.close();
           if (re != null)
               re.close();
       } catch (SQLException e) {
           e.printStackTrace();
       }
   }

   public int excuteUpdate(String sql, Object... str) {
       Connection con = null;
       PreparedStatement pre = null;
       try {
           con = getcon();
           pre = con.prepareStatement(sql);
           if (str != null) {
               for (int i = 0; i < str.length; i++) {
                   pre.setObject(i + 1, str[i]);
               }
           }
           return pre.executeUpdate();

       } catch (SQLException e) {
           e.printStackTrace();
       } finally {
           close(con, pre, null);
       }
       return -1;
   }

   public static int excuteInsert(String sql, Object... str)
           throws SQLException {
       Connection con = null;
       PreparedStatement pre = null;
       ResultSet re = null;
       try {
           con = getcon();
           pre = con.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
           if (str != null) {
               for (int i = 0; i < str.length; i++) {
                   pre.setObject(i + 1, str[i]);
               }
           }
           pre.executeUpdate();
           re = pre.getGeneratedKeys();
           if (re.next()) {
               return re.getInt(1);
           }
       } catch (SQLException e) {
           e.printStackTrace();
       } finally {
           close(con, pre, re);
       }
       return -1;
   }

   public List<Map> excuteQuery(String sql, Object... str) {
       Connection con = null;
       PreparedStatement pre = null;
       ResultSet re = null;
       try {
           con = getcon();
           pre = con.prepareStatement(sql);

           if (str != null) {
               for (int i = 0; i < str.length; i++) {
                   pre.setObject(i + 1, str[i]);
               }
           }
//           pre.executeUpdate();
           re = pre.executeQuery();
           ResultSetMetaData mate = re.getMetaData();
           int count = mate.getColumnCount();

           List list = new ArrayList();
           while (re.next()) {
               Map map = new HashMap();
               for (int i = 1; i <= count; i++) {
                   String lie = mate.getColumnName(i);
                   Object obj = re.getObject(i);
                   map.put(lie.toLowerCase(), obj);
               }
               list.add(map);
           }
           return list;
       } catch (SQLException e) {
           e.printStackTrace();
       } finally {
           close(con, pre, re);
       }
       return null;
   }
}

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