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【后端】黑马MVC案例详解

忧伤小A 2024-07-01 06:01:02

简介【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" %>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="button" value="新增" id="add"><br>
<hr>
<table border="1" cellspacing="0" width="80%">
    <tr>
        <th>序号</th>
        <th>品牌名称</th>
        <th>企业名称</th>
        <th>排序</th>
        <th>品牌介绍</th>
        <th>状态</th>
        <th>操作</th>

    </tr>


    <c:forEach items="${brands}" var="brand" varStatus="status">
//items：被遍历的容器
//var：遍历产生的临时变量
//varStatus：遍历状态对象
//我们这里是从SelectAllServlet跳转过来的，所以接收了request域，我们只管调brand对象输出数据就行
        <tr align="center">
            <%--<td>${brand.id}</td>--%>
            <td>${status.count}</td>
            <td>${brand.brandName}</td>
            <td>${brand.companyName}</td>
            <td>${brand.ordered}</td>
            <td>${brand.description}</td>
            <c:if test="${brand.status == 1}">//这里是JSP，就是if判断
                <td>启用</td>
            </c:if>
            <c:if test="${brand.status != 1}">
                <td>禁用</td>
            </c:if>

            <td><a href="/brandDemo/selectByIdServlet?id=${brand.id}">修改</a> <a href="#">删除</a></td>
        </tr>

    </c:forEach>

</table>

<script>
    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。
</script>
</body>
</html>

addBrand：新增数据

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>添加品牌</title>
</head>
<body>
<h3>添加品牌</h3>
<form action="/brandDemo/addServlet" method="post">//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：<input name="brandName"><br>
    企业名称：<input name="companyName"><br>
    排序：<input name="ordered"><br>
    描述信息：<textarea rows="5" cols="20" name="description"></textarea><br>
    状态：
    <input type="radio" name="status" value="0">禁用
    <input type="radio" name="status" value="1">启用<br>

    <input type="submit" value="提交">
</form>
</body>
</html>

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" %>

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>修改品牌</title>
</head>
<body>
<h3>修改品牌</h3>
<form action="/brandDemo/updateServlet" method="post">//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

    <%--隐藏域，提交id--%>
    <input type="hidden" name="id" value="${brand.id}">

    品牌名称：<input name="brandName" value="${brand.brandName}"><br>
    企业名称：<input name="companyName" value="${brand.companyName}"><br>
    排序：<input name="ordered" value="${brand.ordered}"><br>
    描述信息：<textarea rows="5" cols="20" name="description">${brand.description} </textarea><br>
    状态：
    <c:if test="${brand.status == 0}">

        <input type="radio" name="status" value="0" checked>禁用
        <input type="radio" name="status" value="1">启用<br>
    </c:if>

    <c:if test="${brand.status == 1}">

        <input type="radio" name="status" value="0" >禁用
        <input type="radio" name="status" value="1" checked>启用<br>
    </c:if>


    <input type="submit" value="提交">
</form>
</body>
</html>

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<Brand> 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<Brand> 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<Brand> 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<Brand> 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

风语者！平时喜欢研究各种技术，目前在从事后端开发工作，热爱生活、热爱工作。