JDBC

1. 概念：Java Database Connectivity 一种Java操作数据库的连接技术
2. 步骤：
   1. 选择驱动：从https://search.maven.org/ 上下载mysql-connector-java.jar
   2. 编写连接数据库的代码：
      1. 连接
         `//第1步：加载驱动
         _Class._forName(“com.mysql.jdbc.Driver”);

_//第2步：获得连接
//url username password
_String url = “jdbc:mysql://127.0.0.1:3306/woniuxy?useUnicode=true&characterEncoding=utf8”;

//得到MySQL数据库的连接
_Connection conn = DriverManager._getConnection(url, “root”, “123”);

conn.setAutoCommit(false);_//关闭自动提交

_return conn;`

  1. 查询：
     1. 普通查询：<br />`    _conn _= _ConnecitionUtil.getCon_();<br />    Statement st = _conn_.createStatement();<br />    String sql = "select * from class_info;";<br />    ResultSet rs = st.executeQuery(sql);_//返回结果集_<br />    System._out_.println("id \t名称");<br />    while (rs.next()) {<br />        long id = rs.getLong("id");<br />        String class_name = rs.getString("class_name");<br />        System._out_.println(id + " \t" + class_name);<br />    }<br />    _conn_.close();<br />}`
     1. 预处理+单个返回<br />`    _conn _= ConnectionUtil._getCon_();<br />    String sql = "select * from class_info where id =?";<br />    _pst _= _conn_.prepareStatement(sql);
String id = "1";<br />    _pst_.setString(1, id);<br />    ResultSet set = _pst_.executeQuery(); _//返回结果集_<br />    _//返回第一行<br />    _set.absolute(1);<br />    _//返回第二列<br />_    String className = set.getString(2);<br />    _conn_.close();
return className;`
  3. 增删改<br />`_//返回受影响的行数<br />_rows = _pst_.executeUpdate();`

1. 添加事务
   DBhelper中：
   conn.setAutoCommit(false);_//关闭自动提交_

关闭连接前：
conn.commit();_//提交事务_

1. 存储过程