springboot实战

pom

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.12.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>boot</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>demo</description>
    <url/>
    <licenses>
        <license/>
    </licenses>
    <developers>
        <developer/>
    </developers>
    <scm>
        <connection/>
        <developerConnection/>
        <tag/>
        <url/>
    </scm>
    <properties>
        <java.version>8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.1</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

controller.StudentController

package com.example.demo.controller;


import com.example.demo.pojo.Student;
import com.example.demo.pojo.Users;
import com.example.demo.service.StudentService;
import com.example.demo.service.UsersService;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.ModelAndView;

import javax.annotation.Resource;
import java.util.List;

@RestController
public class StudentController {
    @Resource
    private StudentService studentService;

    @Resource
    private UsersService usersService;

    @GetMapping("/students")
    public ModelAndView getStudentList(Model model) {
        List<Student> studentList = studentService.list();
        model.addAttribute("list", studentList);//和代码中表名list对应，才能进行一系列操作
        ModelAndView modelAndView = new ModelAndView();
        modelAndView.setViewName("list");
        modelAndView.addObject(studentList);
        return modelAndView;
    }

    @GetMapping("/students/{id}")
    @ResponseBody
    public Student getStudentById(@PathVariable(value = "id") int id) {
        return studentService.findById(id);
    }


    @GetMapping("/user/{id}")
    @ResponseBody
    public Users findUser(@PathVariable(value = "id") int id) {
        return usersService.find(id);
    }


}

mapper.StudentMapper

package com.example.demo.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.demo.pojo.Student;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper
public interface StudentMapper extends BaseMapper<Student> {
    List<Student> getStudents();

    Student getStudentById(int id);
}

mapper.UsersMapper

package com.example.demo.mapper;

import com.example.demo.pojo.Users;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import org.apache.ibatis.annotations.Mapper;

/**
 * @author
 * @description 针对表【users】的数据库操作Mapper
 * @createDate 
 * @Entity com.example.demo.pojo.Users
 */
@Mapper
public interface UsersMapper extends BaseMapper<Users> {

    Users find(Integer id);
}

pojo.Student

package com.example.demo.pojo;

import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@NoArgsConstructor
@AllArgsConstructor
@Data
@TableName("users")
public class Student {
    private Integer id;
    private String name;
    private String gender;
    private Integer age;
}

pojo.Users

package com.example.demo.pojo;

import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@NoArgsConstructor
@AllArgsConstructor
@Data
@TableName("users")
public class Student {
    private Integer id;
    private String name;
    private String gender;
    private Integer age;
}

service.impl.Studentimpl

package com.example.demo.service.impl;

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.demo.mapper.StudentMapper;
import com.example.demo.pojo.Student;
import com.example.demo.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class StudentImpl extends ServiceImpl<StudentMapper, Student>  implements StudentService {
    @Autowired
    private StudentMapper studentMapper;

    @Override
    public List<Student> findAll() {
        return studentMapper.getStudents();
    }

    @Override
    public Student findById(int id) {
        return studentMapper.getStudentById(id);
    }
}

service.impl.UsersServiceimpl

package com.example.demo.service.impl;

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.demo.pojo.Users;
import com.example.demo.service.UsersService;
import com.example.demo.mapper.UsersMapper;
import org.springframework.stereotype.Service;

/**
 * @author
 * @description 针对表【users】的数据库操作Service实现
 * @createDate 2
 */
@Service
public class UsersServiceImpl extends ServiceImpl<UsersMapper, Users>
        implements UsersService {

    @Override
    public Users find(int id) {
        return baseMapper.find(id);
    }
}

service.StudentService

package com.example.demo.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.example.demo.pojo.Student;

import java.util.List;
public interface StudentService extends IService<Student> {
    List<Student> findAll();
    Student findById(int id);
}

service.UsersService

package com.example.demo.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.example.demo.pojo.Users;

/**
 * @author 
 * @description 针对表【users】的数据库操作Service
 * @createDate 
 */
public interface UsersService extends IService<Users> {

    Users find(int id);

}

DemoApplication

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

src/main/resources/mapper/StudentMapper.xml

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

<mapper namespace="com.example.demo.mapper.StudentMapper">
    <select id="getStudents" resultType="com.example.demo.pojo.Student">
        select * from users
    </select>
    <select id="getStudentById" resultType="com.example.demo.pojo.Student">
        select * from users where id =#{id}
    </select>
</mapper>

src/main/resources/mapper/UsersMapper.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="com.example.demo.mapper.UsersMapper">

    <resultMap id="BaseResultMap" type="com.example.demo.pojo.Users">
        <id property="id" column="id" jdbcType="INTEGER"/>
        <result property="name" column="name" jdbcType="VARCHAR"/>
        <result property="gender" column="gender" jdbcType="OTHER"/>
        <result property="age" column="age" jdbcType="INTEGER"/>
    </resultMap>

    <sql id="Base_Column_List">
        id
        ,name,gender,
        age
    </sql>
    <select id="find" resultType="com.example.demo.pojo.Users">
        select *
        from users
        where id = #{id}
    </select>
</mapper>

src/main/resources/templates/list.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <!-- 最新版本的 Bootstrap 核心 CSS 文件 -->
    <link href="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/5.3.1/css/bootstrap.min.css" rel="stylesheet">
    <title>Title</title>
</head>
<body>
<div class="container">
    <div class="row clearfix">
        <div class="col-md-12 column">
            <div class="page-header">
                <h1>
                    基于SpringBoot的CRUD案例
                </h1>
            </div>
        </div>
    </div>

    <div class="row">
        <div class="col-md-4 column">
            <a class="btn btn-primary" th:href="@{/add}">新增</a>
        </div>
    </div>

    <div class="row clearfix">
        <div class="col-md-12 column">
            <table class="table table-hover table-striped">
                <thead>
                <td>序号</td>
                <td>ID</td>
                <td>姓名</td>
                <td>性别</td>
                <td>年龄</td>
                <td>编辑</td>
                <td>删除</td>
                </thead>
                <tr th:each="user,stat : ${list}">
                    <td th:text="${stat.count}">序号</td>
                    <td th:text="${user.id}">ID</td>
                    <td th:text="${user.name}">姓名</td>
                    <td th:text="${user.gender}">性别</td>
                    <td th:text="${user.age}">年龄</td>

                    <td><a th:href="@{/update/}+${user.id}">编辑</a></td>
                    <td><a th:href="@{/delete/}+${user.id}" onclick="return confirm('确定要删除该记录吗？')">删除</a></td>
                </tr>
            </table>
        </div>
    </div>
</div>
</body>
</html>

src/main/resources/application.yaml
在idea中springboot项目连接数据库相关文件方法 打开数据连接目标数据库，右键数据库，点击第一项（需要下载插件mybatis=x）填入信息后点击next即可生成相关文件，具体信息可参考student的相关代码文件（上面已经列出来了）

相关代码结果

经验分享：

        1、application.yaml文件里面url可能书写错误

        2、pom文件里面版本冲突  springboot版本改为2.3.12.RELEASE  以及mysql-connector-java

   <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.4.1</version>后，bug消失

        3、mapper文件里的xml中对于resultType书写错误，应为“com.example.demo.pojo.Users”

在一般条件下，pojo里面的名字与mysql的名字有默认的对应关系，必要时需要书写相关的对应关系，例如以下关系

<resultMap id="BaseResultMap" type="com.example.demo.pojo.Users">
        <id property="id" column="id" jdbcType="INTEGER"/>
        <result property="name" column="name" jdbcType="VARCHAR"/>
        <result property="gender" column="gender" jdbcType="OTHER"/>
        <result property="age" column="age" jdbcType="INTEGER"/>
    </resultMap>

       4、书写spingboot的默认文件格式可能错误，与默认关系不服时需要添加必要的代码，详细的具体关系如下图所示

      5、自动生成相关依赖和注解，在setting里输入auto import后点击，对java内的四个选项点击后对号及可完成