javascript - 使用request.gatameter()获取表单数据是为空？？帮忙解决！

Question

表单代码：
<form class="form-horizontal" action="register_logic.jsp" method="post">

                 
                <p class="form-group">
                <p class="col-md-3">
                <input type="text" class="form-control" placeholder="用户名" id="u_name" name="u_name"/>
                </p>
                </p>
                
                <p class="form-group">
                <p class="col-md-3">
                <input type="text" class="form-control" placeholder="电话号码" id="u_phone" name="u_phone"/>
                </p>
                </p>
                
               <p class="form-group">
                <p class="col-md-3">
                <input type="password" class="form-control" placeholder="密码" name="u_password"/>
                </p>
              </p>
              
            <p class="form-group">
                <p class="col-md-3">
                <input type="password" class="form-control" placeholder="再输一次密码" name="password_agin" />
                </p>
            </p>
            
            <p class="form-group">
                <p class="col-md-3">
                 <select class="form-control" name="u_iden">
                  <option value="T">老师</option>
                  <option value="S">学生</option>
                 </select>
               </p> 
            </p>
            
              <p class="form-group">
                 <p class="col-md-4">
                 <input class="btn-primary" type="submit" value="登录" >
                </p>
              </p>
        </form>

jsp为：

    request.setCharacterEncoding("utf-8");
    String phone=request.getParameter("u_phone");
    String name=request.getParameter("u_name");
    String password=request.getParameter("u_password");
    String identity=request.getParameter("u_iden");            

Answer 1

先把代码贴完整吧，servlet怎么写的，而且为什么会用JSP来处理业务逻辑？