【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
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
Title
序号
品牌名称
企业名称
排序
品牌介绍
状态
操作
//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
<%--${brand.id} --%>
${status.count}
${brand.brandName}
${brand.companyName}
${brand.ordered}
${brand.description}
//这里是JSP，就是if判断
启用
禁用
修改 删除
addBrand：新增数据
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
添加品牌
添加品牌
update：修改数据
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
修改品牌
修改品牌
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;
}
@Override
public 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 static SqlSessionFactory 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SqlSession
SqlSession sqlSession = factory.openSession();
//3.获取BrandMapper
BrandMapper 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SqlSession
SqlSession sqlSession = factory.openSession();
//3. 获取BrandMapper
BrandMapper 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SqlSession
SqlSession sqlSession = factory.openSession();
//3. 获取BrandMapper
BrandMapper 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SqlSession
SqlSession sqlSession = factory.openSession();
//3. 获取BrandMapper
BrandMapper 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Servlet
public class SelectAllServlet extends HttpServlet {
private BrandService service = new BrandService();//先创建一个Brand服务对象
@Override
protected 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.jsp
req.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。
}
@Override
protected 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();
@Override
protected 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Servlet
request.getRequestDispatcher("/selectAllServlet").forward(request,response);
}
@Override
protected 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();
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//1、接受id
String 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.jsp
req.getRequestDispatcher("/update.jsp").forward(req,resp);
}
@Override
protected 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();
@Override
protected 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Servlet
req.getRequestDispatcher("/selectAllServlet").forward(req,resp);
}
@Override
protected 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