public class TestJDBC {
    public static void main(String[] args) {
        //数据库连接
        Connection connection = null;
        //预编译的Statement，使用预编译的Statement提高数据库性能
        PreparedStatement preparedStatement = null;
        //结果集
        ResultSet resultSet = null;

        try {
            //加载数据库驱动
            Class.forName("com.mysql.jdbc.Driver");

            //通过驱动管理类获取数据库链接
            connection =  DriverManager.getConnection("jdbc:mysql://172.31.50.116:3306/test_ssm?characterEncoding=utf-8", "root", "123456");
            //定义sql语句 ?表示占位符
            String sql = "select * from _user where user_name = ?";
            //获取预处理statement
            preparedStatement = connection.prepareStatement(sql);
            //设置参数，第一个参数为sql语句中参数的序号（从1开始），第二个参数为设置的参数值
            preparedStatement.setString(1, "阿坚");
            //向数据库发出sql执行查询，查询出结果集
            resultSet =  preparedStatement.executeQuery();
            //遍历查询结果集
            while(resultSet.next()){
                System.out.println(resultSet.getString("user_id")+"  "+resultSet.getString("user_name"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            //释放资源
            if(resultSet!=null){
                try {
                    resultSet.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if(preparedStatement!=null){
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if(connection!=null){
                try {
                    connection.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

        }

    }
}