springBoot和MyBatis-Plus快速开发及分页实战过程

最新推荐文章于 2024-09-30 10:13:27 发布

神奇小白

最新推荐文章于 2024-09-30 10:13:27 发布

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分类专栏： mybatis 文章标签： springBoot MyBatis-Plus springBoot和MyBatis-Plus 分页

本文链接：https://blog.youkuaiyun.com/uotail/article/details/84640418

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项目里面用的MyBatis-Plus这个工具，刚开始各种不好使，熟悉了以后感觉还是很强大的

http://mp.baomidou.com/guide/quick-start.html

按官方的教程写了个demo，不过数据库我换成了mysql，里面还有些问题得注意，

先打开mysql准备数据

现有一张 User 表，其表结构如下：

id	name	age	email
1	Jone	18	test1@baomidou.com
2	Jack	20	test2@baomidou.com
3	Tom	28	test3@baomidou.com
4	Sandy	21	test4@baomidou.com
5	Billie	24	test5@baomidou.com

其对应的数据库 Schema 脚本如下：

DROP TABLE IF EXISTS user;

CREATE TABLE user
(
	id BIGINT(20) NOT NULL COMMENT '主键ID',
	name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
	age INT(11) NULL DEFAULT NULL COMMENT '年龄',
	email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
	PRIMARY KEY (id)
);

其对应的数据库 Data 脚本如下：

DELETE FROM user;

INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, 'test1@baomidou.com'),
(2, 'Jack', 20, 'test2@baomidou.com'),
(3, 'Tom', 28, 'test3@baomidou.com'),
(4, 'Sandy', 21, 'test4@baomidou.com'),
(5, 'Billie', 24, 'test5@baomidou.com');

使用idea自带的 Spring Initializr 快速初始化一个 Spring Boot 工程

pom文件

<?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>com.whale.luo</groupId>
    <artifactId>mybatis-plus</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>mybatis-plus</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <!--idea需要安装lombok插件-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.0.6</version>
        </dependency>

        <!--mysql-->
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.13</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

application.yml

# DataSource Config
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT
    username: root
    password: 12345678

实体

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

注意数据库中的表名默认和实体有着对应关系的，比如
实体User 对应表USER
实体UserAddress对应表USER_ADDRESS
即表名默认是实体名称每个大小写之间加下划线

当然也可以不使用它这种默认的规则，但需要加@TableName注解，比如

@Data
@TableName("USER")
public class UserVo {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

因此，这两个实体是一样的

我们选择第一个使用吧

jdbc测试数据

@RestController
@SpringBootApplication
@MapperScan("com.whale.luo.mybatisplus")
public class MybatisPlusApplication {

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

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @RequestMapping("/getUsers")
    public List<Map<String, Object>> getDbType(){
        String sql = "select * from USER";
        List<Map<String, Object>> list =  jdbcTemplate.queryForList(sql);
        for (Map<String, Object> map : list) {
            Set<Map.Entry<String, Object>> entries = map.entrySet( );
            if(entries != null) {
                Iterator<Map.Entry<String, Object>> iterator = entries.iterator( );
                while(iterator.hasNext( )) {
                    Map.Entry<String, Object> entry =(Map.Entry<String, Object>) iterator.next( );
                    Object key = entry.getKey( );
                    Object value = entry.getValue();
                    System.out.println(key+":"+value);
                }
            }
        }
        return list;
    }

}

运行，访问地址http://localhost:8080/getUsers

接下我们就试试用这个插件实现上面的功能

先创建UserMapper

我们应该继承BaseMappe<T>接口，其中接口中的T应该为我们对应的实体User，不能为其他的，这个插件会自动将根据这个实体去找到它关联的表。

@Component
public interface UserMapper extends BaseMapper<User> {

}

创建接口IUserService及其实现类

在接口中我们也可以声明自己的方法

public interface IUserService extends IService<User> {
    
    List<User> getAll(User user);
    
}

实现类

@Service("iUserService")
public class IUserServiceImpl extends ServiceImpl<UserMapper,User> implements IUserService {
    @Override
    public List<User> getAll(User user) {
        return this.baseMapper.selectList(null);
    }
}

最后的Controller如下

@RestController
@SpringBootApplication
@MapperScan("com.whale.luo.mybatisplus")
public class MybatisPlusApplication {

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

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Autowired
    private IUserService iUserService;

    @RequestMapping("/getUsers")
    public List<Map<String, Object>> getDbType(){
        String sql = "select * from USER";
        List<Map<String, Object>> list =  jdbcTemplate.queryForList(sql);
        for (Map<String, Object> map : list) {
            Set<Map.Entry<String, Object>> entries = map.entrySet( );
            if(entries != null) {
                Iterator<Map.Entry<String, Object>> iterator = entries.iterator( );
                while(iterator.hasNext( )) {
                    Map.Entry<String, Object> entry =(Map.Entry<String, Object>) iterator.next( );
                    Object key = entry.getKey( );
                    Object value = entry.getValue();
                    System.out.println(key+":"+value);
                }
            }
        }
        return list;
    }

    @RequestMapping("/getUserList")
    public List<User> getUserList(){
         User user = new User();
        List<User> all = iUserService.getAll(user);
        //List<User> list = iUserService.list(); 也可以用这个方法返回
        return all;
    }

}

运行http://localhost:8080/getUserList

最后注意：一般我们的实体是不能出现在controller层的，所以我们应当在service层把实体转换成vo再返到前台

流程就是这样，从controller中调服务，再从服务中调mapper

过程中我把service注解加到了接口上，一下子走弯了，这个注解应该加到它的实现类上

内置分页

http://mp.baomidou.com/guide/page.html

直接贴代码

@RestController
@SpringBootApplication
@MapperScan("com.whale.luo.mybatisplus")
public class MybatisPlusApplication {

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

    /**
     * 分页插件
     */
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        return new PaginationInterceptor();
    }

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Autowired
    private IUserService iUserService;

    @RequestMapping("/getUsers")
    public List<Map<String, Object>> getDbType(){
        String sql = "select * from USER";
        List<Map<String, Object>> list =  jdbcTemplate.queryForList(sql);
        for (Map<String, Object> map : list) {
            Set<Map.Entry<String, Object>> entries = map.entrySet( );
            if(entries != null) {
                Iterator<Map.Entry<String, Object>> iterator = entries.iterator( );
                while(iterator.hasNext( )) {
                    Map.Entry<String, Object> entry =(Map.Entry<String, Object>) iterator.next( );
                    Object key = entry.getKey( );
                    Object value = entry.getValue();
                    System.out.println(key+":"+value);
                }
            }
        }
        return list;
    }

    @RequestMapping("/getUserList")
    public List<User> getUserList(){
         User user = new User();
        List<User> all = iUserService.getAll(user);
        //List<User> list = iUserService.list(); 也可以用这个方法返回
        return all;
    }

     @RequestMapping("/selectUserPage")
    public IPage<User> selectUserPage(){
        //Page<User> page = new Page<>(0,0);
        // {"records":[],"total":4,"size":0,"current":1,"searchCount":true,"pages":0}
        // 可以看出"size":0,"current":1,"pages":0 即 一共有0页，每页为0条数据，当前页为第一页

        //Page<User> page = new Page<>(0,1);
        //{"records":[{"id":2,"name":"Jack","age":20,"email":"test2@baomidou.com"}],"total":4,"size":1,"current":1,"searchCount":true,"pages":4}
        //"size":1,"current":1"pages":4   即 一共有4页，每页为1条数据，当前页为第一页

        Page<User> page = new Page<>(1,1);
        //{"records":[{"id":2,"name":"Jack","age":20,"email":"test2@baomidou.com"}],"total":4,"size":1,"current":1,"searchCount":true,"pages":4}
        //可见返回的数据与上条数据一样
        
        //总结new Page<>(1,1);需要传递两个参数，
        // 第一个为current，为当前的页数，默认是从1开始，如果设置为0，它后台是默认请求第一页
        //第二个参数为size ，为每页显示多少条数据,如果为0，则每页为0条数据，所以一般这个值要>=1
        
        IPage<User> userIPage = iUserService.selectUserPage(page);
        return userIPage;
    }

}

分页的时候我们要传一个page参数

总结new Page<>(1,1);需要传递两个参数，
 第一个为current，为当前的页数，默认是从1开始，如果设置为0，它后台是默认请求第一页
第二个参数为size ，为每页显示多少条数据,如果为0，则每页为0条数据，所以一般这个值要>=1

为了测试方便，我直接把page写死了，实际中应该由http请求获得当前页

public interface IUserService extends IService<User> {

    List<User> getAll(User user);

    IPage<User>  selectUserPage(Page<User> page);

}

@Service("iUserService")
public class IUserServiceImpl extends ServiceImpl<UserMapper,User> implements IUserService {
    @Override
    public List<User> getAll(User user) {
        return this.baseMapper.selectList(null);
    }

    public IPage<User> selectUserPage(Page<User> page) {
        return this.baseMapper.selectPage(page,null);
    }
}

运行页面访问 http://localhost:8080/selectUserPage

分页插件 Mybatis-PageHelper

这个插件适用于mybatis，也适用于 mybatis-plus ，因此，下面的操作都是通用的

https://github.com/pagehelper/Mybatis-PageHelper

https://github.com/pagehelper/Mybatis-PageHelper/blob/master/wikis/zh/HowToUse.md使用 *

https://github.com/pagehelper/Mybatis-PageHelper/blob/master/wikis/zh/HowToUse.md 集成springBoot*

https://www.cnblogs.com/ljdblog/p/6725094.html

上面加*号的需要重点看，问题都可在上面找到答案

我的过程如下，还是基于上面接着写

1 pom文件加依赖

       <!--pagehelper-->
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.2.3</version>
        </dependency>

2、修改配置文件application

server:
  port: 8080

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT
    username: root
    password: 12345678
mybatis:
  mapper-locations: classpath:mapping/*Mapper.xml
  type-aliases-package: com.whale.luo.mybatisdemo.po

#pagehelper
pagehelper:
    helperDialect: mysql
    reasonable: true
    supportMethodsArguments: true
    params: count=countSql

3.1、测试1

还是在springBoot的启动类 MybatisPlusApplication上面测试

https://github.com/pagehelper/Mybatis-PageHelper/blob/master/wikis/zh/HowToUse.md#2-pagehelperstartpage-静态方法调用

   @RequestMapping("/selectUserPage1")
    public List<User> selectUserPage1(){
        //获取第1页，2条内容，默认查询总数count
        PageHelper.startPage(1, 2);
        //紧跟着的第一个select方法会被分页
        List<User> list = iUserService.getAll(null);
        return list;
    }

访问http://localhost:8080/selectUserPage1

返回两条数据

[{"id":2,"name":"Jack","age":20,"email":"test2@baomidou.com"},{"id":3,"name":"Tom","age":28,"email":"test3@baomidou.com"}]

3.2 pageInfo测试2

   @RequestMapping("/selectUserPage2")
    public PageInfo selectUserPage2(){

        //获取第1页，10条内容，默认查询总数count
        PageHelper.startPage(1, 1);
        //紧跟着的第一个select方法会被分页
        List<User> list = iUserService.getAll(null);
        //用PageInfo对结果进行包装
        PageInfo pageInfo = new PageInfo(list);
        return pageInfo;
    }

运行 http://localhost:8080/selectUserPage2

确实获得了一条数据，但还有好多其他东西

如下

{
   "pageNum":1, 当前页
   "pageSize":1, 每页显示多少条数据
   "size":1,
   "startRow":1,
   "endRow":1,"
   total":4,
   "pages":4, 一共有4页
   "list":[ 返回的list数据
           {"id":2,"name":"Jack","age":20,"email":"test2@baomidou.com"}
           ],
   "prePage":0,
   "nextPage":2, 下一页
   "isFirstPage":true,
   "isLastPage":false,
   "hasPreviousPage":false,
   "hasNextPage":true,
   "navigatePages":8,
   "navigatepageNums":[1,2,3,4],
   "navigateFirstPage":1,
   "navigateLastPage":4,
   "lastPage":4,
   "firstPage":1
}

这种方法感觉好一点