Java-MVC

MVC模式

• MVC是一种分层开发的模式，其中：

  • M：Model，业务模型，处理业务

  • V：View，视图，界面展示

  • C：Controller，控制器，处理请求，调用模型和视图

• MVC好处
  • 职责单一，互不影响
  • 有利于分工协作
  • 有利于组件重用

三层架构

• 数据访问层：对数据库的CRUD基本操作（Dao包/Mapper包）
• 业务逻辑层：对业务逻辑进行封装，组合数据访问层中基本功能，形成复杂的业务逻辑功能（Service包）
• 表现层：接收请求，封装数据，调用业务逻辑层，相应数据（web包/controller包）

MVC模式和三层架构对照：

案例:

实现需求：

环境准备：

• 创建新的模块brand，引入坐标
• 创建三层架构的包结构
• 数据库表tb_brand
• 实体类Brand
• MyBatis基础环境
  • Mybatis-config.xml
  • BrandMapper.xml
  • BrandMapper接口

过程：

1.首先new一个maven模块brand，配置pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>brand</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>                          //因为是web项目，所以打包变成war

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>

        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.5</version>
        </dependency>

        <!--mysql-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.34</version>
        </dependency>

        <!--servlet-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

        <!--jsp-->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.2</version>
            <scope>provided</scope>
        </dependency>

        <!--jstl-->
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
                <configuration>
                    <uriEncoding>UTF-8</uriEncoding>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

2.引入webapp和WEB-INF，

3.创建mysql数据库，创建tb_brand表

4.创建pojo实体类

package pojo;
/**
 * 品牌实体类
 */

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;


    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 +
                '}';
    }
}

5.配置dao，service，servlet三层包结构

• dao层

  1.BrandMapper类

package mapper;

import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.ResultMap;
import org.apache.ibatis.annotations.Select;
import pojo.Brand;
import java.util.List;

public interface BrandMapper {
    /*查询所有*/

    @Select("select * from tb_brand")
    //@ResultMap("brandResultMap")
    List<Brand> selectAll();

    
}

​ 2.BrandMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper.BrandMapper">
    
</mapper>

• service层

package service;

import mapper.BrandMapper;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import pojo.Brand;
import util.SqlSessionFactoryUtils;

import java.util.List;

public class BrandService {

    SqlSessionFactory factory = SqlSessionFactoryUtils.getSqlSessionFactory();

    /*调用BrandMapper.selectAll()查询所有*/
    public List<Brand> selectAll()
    {

        SqlSession sqlSession = factory.openSession();

        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        List<Brand> brands = mapper.selectAll();

        sqlSession.close();

        return brands;
    }

  
}

• web层

package web;

import pojo.Brand;
import 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")
public class SelectAllServlet extends HttpServlet {
    private BrandService brandService = new BrandService();
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//        request.setCharacterEncoding("UTF-8");         //在表单提交时需要处理编码问题
//        response.setContentType("text/html;charset=UTF-8");
        /*调用BrandService完成查询*/
        List<Brand> brands = brandService.selectAll();

        /*存入request域中*/
        request.setAttribute("brands",brands);

        /*转发brand.jsp中*/
        request.getRequestDispatcher("/brand.jsp").forward(request,response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}

• util包

  package 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;
  
      static {
          //静态代码块会随着类的加载而自动执行，且只执行一次
  
          try {
              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;
      }
  }

6.Mybatis环境

配置Mybatis，连接本机数据库

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!--起别名-->
    <!--<typeAliases>
        <package name="pojo"/>
    </typeAliases>-->

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///test?useSSL=false&amp;useServerPrepStmts=true"/>
                <property name="username" value="root"/>
                <property name="password" value="xyh"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--扫描mapper-->
        <package name="mapper"/>
    </mappers>
</configuration>

7.brand.jsp显示页面：

<%@ page contentType="text/html;classset = UTF-8" pageEncoding="utf-8" language="java" %>
<%@ taglib prefix="c" uri = "http://java.sun.com/jsp/jstl/core" %>
<%--<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>--%>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>SelectAllServlet</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">

        <tr align="center">
            <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}">
                <td>启用</td>
            </c:if>
            <c:if test="${brand.status != 1}">
                <td>禁用</td>
            </c:if>
            <td><a href= "#">修改  </a><a href= "#">删除</a></td>
        </tr>

    </c:forEach>


</table>
</hr>

<script>
    document.getElementById("add").onclick = function () {
        location.herf = "/brand/addBrand.jsp";
    }
</script>
</body>
</html>

学习总结：

在三层框架学习中，遇到了很多问题和注意事项，记录一下~

1.路径问题，

Servlet中的@Website注解大小写一定与html需要转发跳转的路径相同。

2.注意打包，因为是web项目，必须打包成war

3.编码问题，启动服务器后发现页面呈现乱码

• 最初情况

对于以下这种情况，首先检查浏览器编码是否正确，下载浏览器charset插件，将浏览器页面改为UTF-8编码。

• 修改完浏览器页面编码之后，发现有些地方中文显示问号。

此时，检查自己的数据库编码，tomcat配置文件编码以及IDEA中web项目编码是否均为utf-8，如果都没问题，

• 此时，应该就是jsp文件的问题，我们需要在引用标签里增加以下标签即可。

  pageEncoding="utf-8"

大功告成：

然后，放一下IDEA中的目录结构吧，就当回想以下maven结构了~~

最后，放上帮助我解决编码问题大佬的博客链接：

https://blog.csdn.net/u012611878/article/details/80723491?spm=1001.2101.3001.6650.1&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.pc_relevant_paycolumn_v2&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.pc_relevant_paycolumn_v2&utm_relevant_index=2