【后端】黑马MVC案例详解

最近刚入门后端，对不起，我背叛了游戏【哭】

跟着写了一个这样的案例

网页界面是这样的

没写删除，里面带有增加行和修改表单数据的功能

web方面就三个页面，里面涉及到了Mybatis，Tomcat，JSP，Servlet，Maven，前端三剑客等知识，东西比较杂，我也是速通选手，掌握不太稳固，所以写个文章巩固一下知识点，以便自己能够更好地理解代码以及运行逻辑。

项目结构是这样的，需要配置mybatis-config.xml文件，pom.xml需要引入tomcat、Servlet，mybatis，JSP，Maven写个标识就能自动下载了，Maven好方便

以及Mapper配置文件和web配置文件，不是很复杂。

我们的代码方面

一、前端页面

三个前端页面分别是这样的

brand：主页面

//items：被遍历的容器//var：遍历产生的临时变量//varStatus：遍历状态对象//我们这里是从SelectAllServlet跳转过来的，所以接收了request域，我们只管调brand对象输出数据就行<%----%>//这里是JSP，就是if判断
序号
品牌名称
企业名称
排序
品牌介绍
状态
操作
${brand.id}
${status.count}
${brand.brandName}
${brand.companyName}
${brand.ordered}
${brand.description}
启用
禁用
修改 删除
document.getElementById("add").onclick = function (){location.href = "/brandDemo/addBrand.jsp";}//这里使用getElementById设置了按钮的点击事件。

addBrand：新增数据

添加品牌
//这里我们提交到addServlet服务，还是以POST形式，然后addServlet再转发到brand.jsp页面品牌名称：
企业名称：
排序：
描述信息：
状态：禁用启用

update：修改数据

修改品牌
//这里还是一样的，提交到updateServlet服务当中//这里跟新增表单页面没什么大的不同，但是Servlet方面就要先查询再修改，还是比新增麻烦的品牌名称：
企业名称：
排序：
描述信息：${brand.description} 
状态：禁用启用
禁用启用

二、mybatis操作方面

既然处理数据肯定是要学习mybatis的

操作不难，写几个接口就行

这里则是使用到mapper的知识，不得不说，javaweb学的东西是真的杂，学的时候天天导包配文件，累。

BrandMapper:

package com.itheima.mapper;import com.itheima.pojo.Brand;import org.apache.ibatis.annotations.Insert;import org.apache.ibatis.annotations.ResultMap;import org.apache.ibatis.annotations.Select;import org.apache.ibatis.annotations.Update;import java.util.List;public interface BrandMapper {//这里也没啥好说的，以注解形式操纵数据库，都是一些基础操作语句//唯一值得注意的是当我们两种模式命名有冲突的时候我们要配置ResultMap//使得我们Brand查询的时候能找到对应的变量/*查询所有@return */@Select("select * from tb_brand")@ResultMap("brandResultMap")List selectAll();@Insert("insert into tb_brand values(null,#{brandName},#{companyName},#{ordered},#{description},#{status})")void add(Brand brand);/** * 根据id查询 * @param id * @return */@Select("select * from tb_brand where id = #{id}")@ResultMap("brandResultMap")Brand selectById(int id);/** * 修改 * @param brand */@Update("update tb_brand set brand_name = #{brandName},company_name = #{companyName},ordered = #{ordered},description = #{description},status = #{status} where id = #{id}")void update(Brand brand);}

brand数据类：

package com.itheima.pojo;public class Brand {// id 主键private Integer id;// 品牌名称private String brandName;// 企业名称private String companyName;// 排序字段private Integer ordered;// 描述信息private String description;// 状态：0：禁用1：启用private Integer status;//提供了三种构造方法以备不同情况，是一些面向对象的特性，Java学过的都能懂public Brand() {}public Brand(Integer id, String brandName, String companyName, String description) {this.id = id;this.brandName = brandName;this.companyName = companyName;this.description = description;}public Brand(Integer id, String brandName, String companyName, Integer ordered, String description, Integer status) {this.id = id;this.brandName = brandName;this.companyName = companyName;this.ordered = ordered;this.description = description;this.status = status;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getBrandName() {return brandName;}public void setBrandName(String brandName) {this.brandName = brandName;}public String getCompanyName() {return companyName;}public void setCompanyName(String companyName) {this.companyName = companyName;}public Integer getOrdered() {return ordered;}public void setOrdered(Integer ordered) {this.ordered = ordered;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public Integer getStatus() {return status;}public void setStatus(Integer status) {this.status = status;}@Overridepublic String toString() {return "Brand{" +"id=" + id +", brandName='" + brandName + '\'' +", companyName='" + companyName + '\'' +", ordered=" + ordered +", description='" + description + '\'' +", status=" + status +'}';}}

三、Servlet服务

这里就是处理数据的大头了

因为创建工厂类只用一次就能最节省资源，所以我们用一个SqlSessionFactoryUtils静态类来封装好，下次直接调函数就行了，这里还是操作mybatis的东西

package com.itheima.util;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;public class SqlSessionFactoryUtils {private static SqlSessionFactory sqlSessionFactory;//静态对象static {try{//这里是数据库连接必写的三句String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);}catch (IOException e){e.printStackTrace();}}public staticSqlSessionFactory getSqlSessionFactory(){return sqlSessionFactory;//用的时候直接调这个方法}}

随后写BrandService，这里是将对数据的操作全都封装好，免得到时候麻烦

代码是这样的

package com.itheima.service;import com.itheima.mapper.BrandMapper;import com.itheima.pojo.Brand;import com.itheima.util.SqlSessionFactoryUtils;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import java.util.List;public class BrandService {SqlSessionFactory factory = SqlSessionFactoryUtils.getSqlSessionFactory();//这里获取工厂类/*查询所有@return */public List selectAll(){//查询所有//调用BrandMapper.selectAll()//2.获取SqlSessionSqlSession sqlSession = factory.openSession();//3.获取BrandMapperBrandMapper mapper = sqlSession.getMapper(BrandMapper.class);//4.调用方法List brands = mapper.selectAll();//这里就是操作数据库，然后封装到一个brands列表里sqlSession.close();return brands;//返回查询到的值}/** * 添加 * @param brand */public void add(Brand brand){//这里是添加//2. 获取SqlSessionSqlSession sqlSession = factory.openSession();//3. 获取BrandMapperBrandMapper mapper = sqlSession.getMapper(BrandMapper.class);//4. 调用方法mapper.add(brand);//往数据库里添加一个brand对象//提交事务sqlSession.commit();//释放资源sqlSession.close();}/** * 根据id查询 * @return */public Brand selectById(int id){//依靠id查询对象//调用BrandMapper.selectAll()//2. 获取SqlSessionSqlSession sqlSession = factory.openSession();//3. 获取BrandMapperBrandMapper mapper = sqlSession.getMapper(BrandMapper.class);//4. 调用方法Brand brand = mapper.selectById(id);sqlSession.close();return brand;}/** * 修改 * @param brand */public void update(Brand brand){//修改值//2. 获取SqlSessionSqlSession sqlSession = factory.openSession();//3. 获取BrandMapperBrandMapper mapper = sqlSession.getMapper(BrandMapper.class);//4. 调用方法mapper.update(brand);//提交事务sqlSession.commit();//释放资源sqlSession.close();}}

然后是Servlet服务类

通过这些服务我们来操作网页里的数据

SelectAllServlet：

package com.itheima.web;import com.itheima.pojo.Brand;import com.itheima.service.BrandService;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.util.List;@WebServlet("/selectAllServlet")//这里我们通过标签访问Servletpublic class SelectAllServlet extends HttpServlet {private BrandService service = new BrandService();//先创建一个Brand服务对象@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//1、调用BrandService完成查询List brands = service.selectAll();//这里我们直接调用查询//2、存入request域中req.setAttribute("brands",brands);//存入request域，到时候发出去的就是这个，要查询的话只要调用键查值就行了，request域都是键值对。//3、转发到brand.jspreq.getRequestDispatcher("/brand.jsp").forward(req,resp);//这里我们调用getrequestDispatcher方法转发到brand.jsp页面中，再通过JSP代码把数据显示出来。}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doGet(req,resp);//这样写能同时响应POST请求和GET请求}}

AddServlet:

package com.itheima.web;import com.itheima.pojo.Brand;import com.itheima.service.BrandService;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/addServlet")public class AddServlet extends HttpServlet {private BrandService service = new BrandService();@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//处理POST请求的乱码问题request.setCharacterEncoding("utf-8");//1. 接收表单提交的数据，封装为一个Brand对象String brandName = request.getParameter("brandName");String companyName = request.getParameter("companyName");String ordered = request.getParameter("ordered");String description = request.getParameter("description");String status = request.getParameter("status");//封装为一个Brand对象Brand brand = new Brand();brand.setBrandName(brandName);brand.setCompanyName(companyName);brand.setOrdered(Integer.parseInt(ordered));brand.setDescription(description);brand.setStatus(Integer.parseInt(status));//2. 调用service 完成添加service.add(brand);//3. 转发到查询所有Servletrequest.getRequestDispatcher("/selectAllServlet").forward(request,response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}}

SelectById:

package com.itheima.web;import com.itheima.pojo.Brand;import com.itheima.service.BrandService;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/selectByIdServlet")public class SelectByIdServlet extends HttpServlet {private BrandService service = new BrandService();@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//1、接受idString id = req.getParameter("id");//2、调用service查询Brand brand = service.selectById(Integer.parseInt(id));//3、存储到request中req.setAttribute("brand",brand);//4、转发到update.jspreq.getRequestDispatcher("/update.jsp").forward(req,resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doGet(req, resp);}}

Updateservlet:

package com.itheima.web;import com.itheima.pojo.Brand;import com.itheima.service.BrandService;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/updateServlet")public class UpdateServlet extends HttpServlet {private BrandService service = new BrandService();@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//处理POST请求的乱码问题req.setCharacterEncoding("utf-8");//1、接受表单提交的数据String id = req.getParameter("id");String brandName = req.getParameter("brandName");String companyName = req.getParameter("companyName");String ordered = req.getParameter("ordered");String description = req.getParameter("description");String status = req.getParameter("status");//封装为一个Brand对象Brand brand = new Brand();brand.setId(Integer.parseInt(id));brand.setBrandName(brandName);brand.setCompanyName(companyName);brand.setOrdered(Integer.parseInt(ordered));brand.setDescription(description);brand.setStatus(Integer.parseInt(status));//2、调用serice完成修改service.update(brand);//3、转发到查询所有Servletreq.getRequestDispatcher("/selectAllServlet").forward(req,resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doGet(req, resp);}}

代码差不多就这样了，做完发现东西还挺多的，面向对象要写的东西还是挺多的。

下面是逻辑的梳理，说实话梳理逻辑确实是要花上一些时间

展现brand页面：通过查询tb_brand和JSP以及HTML、CSS来展现出数据库里的数据

访问顺序：SelectAll.class->brand.jsp

新增数据：填写表单数据->在数据库中实现添加->addServlet->selectAllServlet->发送到brand.jsp->展现数据

访问顺序：brand.jsp->AddServlet.class->update.jsp->SelectAllServlet.class->brand.jsp

修改数据：通过查询当前id所对应的表将其发送到update.jsp0界面->填写修改后的数据->提交表单数据->在数据库中实现修改->查询所有->brand.jsp展现数据

访问顺序：brand.jsp->SelectByIdServlet->update.jsp->updateServlet->SelectAllServlet->brand.jsp