JDBC连接数据库

1.安装tomcat、mysql、及idea，安装事宜具体不多讲
2.下载mysql-connector-java-8.0.20.jar
下载地址:https://mvnrepository.com/artifact/mysql/mysql-connector-java/8.0.20
3.将下载完的mysql-connector-java-8.0.20.jar放到tomcat中的/WEB-INF/lib文件夹中 并添加到项目中
4.代码示例:

   //此处需要注意的是mysql-connector-java的版本不同，获取驱动类名也不同
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";//com.mysql.jdbc.Driver 是 mysql-connector-java 5及5之前的
    static final String JDBC_DRIVERNEW = "com.mysql.cj.jdbc.Driver";//com.mysql.cj.jdbc.Driver 是 mysql-connector-java 6及6之后的的
    //参数解释 jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8
    //jdbc:连接数据库方式 localhost:请求地址 3306:数据库端口号 test数据库名称
    //useUnicode=true&characterEncoding=utf-8 请求数据库编码方式此处必须要，否则插入数据为乱码 
//serverTimezone=UTC 设置时区，必须要设置
    static final String DB_URL = "jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&serverTimezone=UTC";

    // 数据库的用户名与密码，需要根据自己的设置
    static final String USER = "root";
    static final String PASS = "123456";

 Connection conn = null;
    Statement stmt = null;
@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("utf-8");
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        String user =  req.getParameter("user");
       /* System.out.println("user ="+user);
        req.setAttribute("user",user);
        req.getRequestDispatcher("hello.jsp").forward(req,resp);*/
        try{
            // 注册 JDBC 驱动器
            Class.forName(JDBC_DRIVERNEW);
            // 打开一个连接
           conn = DriverManager.getConnection(DB_URL,USER,PASS);
            // 执行 SQL 查询
            stmt = conn.createStatement();
            String sql；
            sql = "SELECT * FROM login";
            ResultSet rs = stmt.executeQuery(sql);
            while (rs.next()){
                String user1 = rs.getString("user");
                String pas1 = rs.getString("pas");
                System.out.println(user1+pas1);
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }