老师，后台分类插入只有最后修改时间

package com.lmz.book.dao;

import com.lmz.book.entity.Category;
import com.sun.org.apache.xml.internal.resolver.Catalog;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import java.util.Date;
import java.util.List;

public interface CategoryDao {
   @Insert("insert into category(name) value(#{name})")
   void insert(String name);

   @Select("select * from category order by create_time asc")
   @Results(id = "all",value = {
           @Result(column = "id",property = "id",id=true),
           @Result(column = "name",property = "name"),
           @Result(column = "create_time",property = "createTime"),
           @Result(column = "update_time",property = "updateTime")
   })
   List<Category> select();


}

package com.lmz.book.controller;

import com.lmz.book.biz.CategoryBiz;
import com.lmz.book.biz.impl.CategoryBizImpl;
import com.lmz.book.entity.Category;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

public class CategoryController {
   private CategoryBiz categoryBiz=new CategoryBizImpl();
   public void list(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       List<Category> categoryList = categoryBiz.getAll();
       request.getServletContext().setAttribute("categoryList",categoryList);
       request.getRequestDispatcher("/WEB-INF/pages/admin/category_list.jsp").forward(request,response);
   }

   public void toAdd(HttpServletRequest request,HttpServletResponse response) throws IOException, ServletException {
       List<Category> categoryList = categoryBiz.getAll();
       request.getServletContext().setAttribute("categoryList",categoryList);
       request.getRequestDispatcher("/WEB-INF/pages/admin/category_toAdd.jsp").forward(request,response);
   }

   public void save(HttpServletRequest request,HttpServletResponse response) throws IOException {
       Category category=new Category();
       category.setName(request.getParameter("name"));
       categoryBiz.save(category);
       response.sendRedirect("list.do");
   }
}

public class Category {
   private int id;
   private String name;
   private Date createTime;
   private Date updateTime;
   private List<Book> bookList=new ArrayList<Book>();

   public List<Book> getBookList() {
       return bookList;
   }

   public void setBookList(List<Book> bookList) {
       this.bookList = bookList;
   }

麻烦老师帮忙看下，另外老师，其实我不是很懂这里时间的获取是怎么得到的，我的代码里插入的只有一个string类型的name，现在得到的这个时间貌似应该是创建时间？但是我不清楚这个时间是怎么获得的