jdbc练习demo

//连接云端服务器数据库工具类
public class TestJDBCUtil {	
	    public static String driver="com.mysql.jdbc.Driver";
	    public static String url = "jdbc:mysql://42.123.87.49:3306/aaaaa?useUnicode=true&characterEncoding=utf-8";
	    public static String user = "***";
	    public static String password = "****";
	    //获取1条数据库的连接
	    private static Connection getConnection()
	    {
	        Connection con = null;  //返回的连接
	        try {
	            //1 加载驱动
	            Class.forName(driver);
	            con = DriverManager.getConnection(url, user, password);
	            
	            //2 获取连接
	        } catch (Exception e)
	        {
	            e.printStackTrace();
	        }
	        return con;
	    }
	  //查询：简单查询，不含？的sql语句
	    public static  ResultSet doQuery(String sql)
	    {
	        return doQuery(sql,null);
	    }
	  //查询：复杂查询，含有多个？的sql语句
	    public static  ResultSet doQuery(String sql,String... ps)
	    {
	        //1 获取连接
	        Connection con = getConnection(); //调用上面的方法，获取1个连接
	        if(con==null)
	        {
	            System.out.println("获取连接失败！");
	            return null; //提前终止本方法代码
	        }	 
	        ResultSet rs = null;
	        try {
	            //2执行查询
	            PreparedStatement psm = con.prepareStatement(sql);
	            //通过for循环，访问参数数组，给psm逐个设置可变参数！！
	            if(ps!=null) //只有可变参数不为空，才进行?赋值
	            {
	                for(int i=0;i<ps.length;i++)
	                {
	                    psm.setString(i+1, ps[i]);//将第i个可变参数，设置到第i+1个问号
	                }
	            }
	            rs = psm.executeQuery();
	        } catch (Exception e)
	        {
	            e.printStackTrace();
	        }
	        //3 返回结果
	        return rs;
	    }
	  //关闭资源。
	    public static void close(ResultSet rs)
	    {
	        Statement sm = null;
	        Connection con = null;
	        try {
	            if (rs != null)
	            {
	                sm = rs.getStatement();
	                rs.close();
	            }	 
	            if (sm != null)
	            {
	                con = sm.getConnection();
	                sm.close();
	            }          
	            if (con != null)
	                con.close();
	        } catch (Exception e)
	        {      
	            e.printStackTrace();
	        }      
	    }
	    public static void main(String[] args) {
	    	String sql="SELECT * FROM cj_scenedatadetail";
	    	ResultSet rs =TestJDBCUtil.doQuery(sql);
	    	int i=0;
	    	//System.out.println(rs+"***");
	    	try {
				while (rs.next()) {						        
			        String retainedCount = rs.getString("content_varchar");			        
			        System.out.println(" 留存信息："+retainedCount);
			       i++; 
				} 
				System.out.println("留存总数量："+(i-1));
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
}