jdbc连接数据库工具类

 import java.lang.reflect.Field;
 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.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;

 public class DBUtils {

     // 表示定义数据库的用户名
     private static String USERNAME = "root";
     // 定义数据库的密码
     private static String PASSWORD = "root";
     // 定义数据库的驱动信息
     private static String DRIVER = "com.mysql.jdbc.Driver";
     // 定义访问数据库的地址
     private static String URL = "jdbc:mysql://localhost:3306/db";

     private static DBUtils per = null;
     // 定义数据库的链接
     private Connection con = null;
     // 定义sql语句的执行对象
     private PreparedStatement pstmt = null;
     // 定义查询返回的结果集合
     private ResultSet resultSet = null;

     private DBUtils() {

     }

     /**
      * 单例模式，获得工具类的一个对象
      *
      * @return
      */
     public static DBUtils getInstance() {
         if (per == null) {
             per = new DBUtils();
             per.registeredDriver();
         }
         return per;
     }

     private void registeredDriver() {
         // TODO Auto-generated method stub
         try {
             Class.forName(DRIVER);
             System.out.println("注册驱动成功！");
         } catch (ClassNotFoundException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }

     /**
      * 获得数据库的连接
      *
      * @return
      */
     public Connection getConnection() {
         try {
             con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
         } catch (SQLException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         System.out.println("连接数据库成功!!");
         return con;
     }

     /**
      * 完成对数据库的表的添加删除和修改的操作
      *
      * @param sql
      * @param params
      * @return
      * @throws SQLException
      */
     public boolean executeUpdate(String sql, List<Object> params)
             throws SQLException {

         boolean flag = false;

         int result = -1;  // 表示当用户执行添加删除和修改的时候所影响数据库的行数

         pstmt = con.prepareStatement(sql);

         if (params != null && !params.isEmpty()) {
             int index = 1;
             for (int i = 0; i < params.size(); i++) {
                 pstmt.setObject(index++, i);
             }
         }

         result = pstmt.executeUpdate();
         flag = result > 0 ? true : false;

         return flag;
     }

     /**
      * 从数据库中查询数据
      *
      * @param sql
      * @param params
      * @return
      * @throws SQLException
      */
     public List<Map<String, Object>> executeQuery(String sql,
             List<Object> params) throws SQLException {
         List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
         int index = 1;
         pstmt = con.prepareStatement(sql);
         if (params != null && !params.isEmpty()) {
             for (int i = 0; i < params.size(); i++) {
                 pstmt.setObject(index++, params.get(i));
             }
         }
         resultSet = pstmt.executeQuery();
         ResultSetMetaData metaData = resultSet.getMetaData();
         int cols_len = metaData.getColumnCount();
         while (resultSet.next()) {
             Map<String, Object> map = new HashMap<String, Object>();
             for (int i = 0; i < cols_len; i++) {
                 String cols_name = metaData.getColumnName(i + 1);
                 Object cols_value = resultSet.getObject(cols_name);
                 if (cols_value == null) {
                     cols_value = "";
                 }
                 map.put(cols_name, cols_value);
             }
             list.add(map);
         }
         return list;

     }

     /**
      * jdbc的封装可以用反射机制来封装,把从数据库中获取的数据封装到一个类的对象里
      *
      * @param sql
      * @param params
      * @param cls
      * @return
      * @throws Exception
      */
     public <T> List<T> executeQueryByRef(String sql, List<Object> params,
             Class<T> cls) throws Exception {
         List<T> list = new ArrayList<T>();
         int index = 1;
         pstmt = con.prepareStatement(sql);
         if (params != null && !params.isEmpty()) {
             for (int i = 0; i < params.size(); i++) {
                 pstmt.setObject(index++, params.get(i));
             }
         }
         resultSet = pstmt.executeQuery();
         ResultSetMetaData metaData = resultSet.getMetaData();
         int cols_len = metaData.getColumnCount();
         while (resultSet.next()) {
             T resultObject = cls.newInstance();  // 通过反射机制创建实例
             for (int i = 0; i < cols_len; i++) {
                 String cols_name = metaData.getColumnName(i + 1);
                 Object cols_value = resultSet.getObject(cols_name);
                 if (cols_value == null) {
                     cols_value = "";
                 }
                 Field field = cls.getDeclaredField(cols_name);
                 field.setAccessible(true); // 打开javabean的访问private权限
                 field.set(resultObject, cols_value);
             }
             list.add(resultObject);
         }
         return list;

     }

     public void closeDB() {
         if (resultSet != null) {
             try {
                 resultSet.close();
             } catch (SQLException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
         if (pstmt != null) {
             try {
                 pstmt.close();
             } catch (SQLException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
         if (con != null) {
             try {
                 con.close();
             } catch (SQLException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
     }

 }

测试：

 import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;

 public class Test {

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub

         DBUtils db = DBUtils.getInstance();
         db.getConnection();
         String sql = "SELECT name,introduction,location FROM activity WHERE id IN(SELECT activityId from mem_act_collect where memberId = ?)";
         List<Activity> reslist = new ArrayList<Activity>();
         List<Object> list = new ArrayList<Object>();
         list.add(2014303342);

         try {
             reslist = db.executeQueryByRef(sql,list,Activity.class);

             for(Activity ac:reslist){
                 System.out.println(ac.toString());
             }

         } catch (Exception e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }finally{
             db.closeDB();
         }

     }

 }