springboot中controller层接收参数，servers层调用mapper层，一条sql搞定排序

前言
很多小伙伴们在公司不管是测试C端产品还是B端产品，都会测到排序的业务需求；那么我们就会好奇排序是如何实现的呢？下面我们开始介绍代码的实现

数据库建表
我们需要创建一个书籍book表结构，如下图所示

CREATE TABLE `book` (
`id` int(11) NOT NULL AUTO_INCREMENT comment '主键自增id',
`book_no` varchar(200) comment '书的编号',
`book_name` varchar(200) NOT NULL comment '书名',
`book_author` varchar(200) DEFAULT NULL comment '书的作者',
`book_publish` varchar(200) DEFAULT NULL comment '书的出版社',
`book_category` int(11) DEFAULT NULL comment '书的分类',
`book_price` varchar(20) DEFAULT NULL comment '书的价格',
`book_introduction` text DEFAULT NULL comment '书的介绍',
create_time timestamp not null default current_timestamp comment '创建时间',
update_time timestamp not null default current_timestamp on update current_timestamp comment '更新时间',
PRIMARY KEY (`id`),
KEY `book_category` (`book_category`) USING BTREE,
CONSTRAINT `book_ibfk_1` FOREIGN KEY (`book_category`) REFERENCES `book_category` (`category_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 comment '书的信息';

向book表里插入数据

insert into book(book_no,book_name,book_author,book_publish,book_category,book_price,book_introduction) 
values('1111','巨人的陨落','肯.福莱特','江苏凤凰文艺出版社',1,'129','一本文学巨作');
insert into book(book_no,book_name,book_author,book_publish,book_category,book_price,book_introduction) 
values('2222','巨人的陨落2','肯.福莱特','江苏凤凰文艺出版社',1,'129','一本文学巨作');
insert into book(book_no,book_name,book_author,book_publish,book_category,book_price,book_introduction)
values('3333','巨人的陨落3','肯.福莱特','江苏凤凰文艺出版社',1,'129','一本文学巨作');
insert into book(book_no,book_name,book_author,book_publish,book_category,book_price,book_introduction) 
values('4444','巨人的陨落4','肯.福莱特','江苏凤凰文艺出版社',1,'129','一本文学巨作');
insert into book(book_no,book_name,book_author,book_publish,book_category,book_price,book_introduction)
values('5555','巨人的陨落5','肯.福莱特','江苏凤凰文艺出版社',1,'129','一本文学巨作');
insert into book(book_no,book_name,book_author,book_publish,book_category,book_price,book_introduction) 
values('6666','巨人的陨落6','肯.福莱特','江苏凤凰文艺出版社',1,'129','一本文学巨作');
insert into book(book_no,book_name,book_author,book_publish,book_category,book_price,book_introduction) 
values('7777','巨人的陨落7','张三','江苏凤凰文艺出版社',1,'129','一本文学巨作');

创建mapper.xml文件

• include标签语法：include是引用SQL代码，refid 是引用的sql的id名称，一定要唯一
• where标签语法：是顶层的遍历标签，需要配合if标签使用，单独使用无意义。
• if标签语法：主要用来进行条件查询或者解决空值插入。具体语法为：<if test="校验条件">sql语句</if>
• resultType标签语法：当数据表中字段的名称和实体类的属性名一致时,MyBatis会自动把查询结果集中的属性赋值给和bean对象类中的属性名一致的字段。可以使用此标签进行映射

resultMap标签语法：当数据表中字段的名称和实体类的属性名不一致时，使用此标签进行映射。
语法格式：
<resultMap type="实体类" id="唯一的标志"><result column="数据表字段" property="实体属性"/></resultMap>
这个id是resultMap的唯一标识 在select标签要引用这个resultMap时 靠这个id来引用就行
<select id="getBookList" resultMap="bookMap">

<?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.o2o.mapper.BookMapper">
    <!-- 书籍对象映射 -->
    <resultMap id="bookMap" type="com.o2o.data.Book">
        <id column="id" property="id"/>
        <id column="book_no" property="bookNo"/>
        <id column="book_name" property="bookName"/>
        <id column="book_author" property="bookAuthor"/>
        <id column="book_publish" property="bookPublish"/>
        <id column="book_category" property="bookCategory"/>
        <id column="book_price" property="bookPrice"/>
        <id column="book_introduction" property="bookIntroduction"/>
        <id column="category_name" property="categoryName"/>
        <id column="create_time" property="createTime"/>
        <id column="update_time" property="updateTime"/>
    </resultMap>

    <!-- 书籍对象映射 -->
    <resultMap type="com.o2o.data.BookWithBorrowFlg" id="bookWithBorrowFlgMap">
        <id column="id" property="id"/>
        <id column="book_no" property="bookNo"/>
        <id column="book_name" property="bookName"/>
        <id column="book_author" property="bookAuthor"/>
        <id column="book_publish" property="bookPublish"/>
        <id column="book_category" property="bookCategory"/>
        <id column="book_price" property="bookPrice"/>
        <id column="book_introduction" property="bookIntroduction"/>
        <id column="category_name" property="categoryName"/>
        <id column="create_time" property="createTime"/>
        <id column="update_time" property="updateTime"/>
        <id column="username" property="username"/>
        <id column="borrow_flg" property="borrowFlg"/>
    </resultMap>

    <!-- 按照查询条件分页查询书籍  -->
     <select id="getBookList" resultMap="bookMap">
         select
         a.id,a.book_no,a.book_name,a.book_author,a.book_publish,a.book_price,a.book_introduction,b.category_name
         from
         book a
         inner join
         book_category b
         on a.book_category = b.category_id
         <include refid="getBooksWhere"></include>
         order by a.update_time desc
     </select>

    <!-- 获取书籍的动态where条件 -->
    <sql id="getBooksWhere">
    <where>
    1=1
        <if test="bookNo != null and bookNo != ''">
            and a.book_no like '%' #{bookNo} '%'
        </if>
        <if test="bookName != null and bookName != ''">
            and a.book_name like '%' #{bookName} '%'
        </if>
        <if test="bookAuthor != null and bookAuthor != ''">
            and a.book_author like '%' #{bookAuthor} '%'
        </if>
        <if test="bookPublish != null and bookPublish != ''">
            and a.book_publish like '%' #{bookPublish} '%'
        </if>
        <if test="bookCategory != null and bookCategory != ''">
            and a.book_category = #{bookCategory}
        </if>
    </where>
    </sql>
</mapper>

application.yml配置文件

• driver-class-name: com.mysql.cj.jdbc.Driver
  mysql是8.x版本的需要加cj,如果是低版本5.x的不需要加这个cj
• mapper-locations: classpath:/mapper/*.xml
  #classpath指的是resource文件夹指定mapper文件的位置，将配置路径下的*.xml文件加载到mybatis
• map-underscore-to-camel-case: true
  开启驼峰命名规则 比如数据库字段是有下划线的t_no,那么代码中就要写成Tno代码里面自动把下划线的字母变成大写

server:
  port: 9527

# 数据源
spring:
  datasource:
    druid:
      driver-class-name: com.mysql.cj.jdbc.Driver  # mysql是8.x版本的需要加cj,如果是低版本5.x的不需要加这个cj
      url: jdbc:mysql://localhost:3306/cyw-mybatis?autoReconnect=true&useSSL=false&useUnicode=true&characterEncoding=UTF-8
      username: root
      password: ******


mybatis:
  #classpath指的是resource文件夹指定mapper文件的位置，将配置路径下的*.xml文件加载到mybatis
  mapper-locations: classpath:/mapper/*.xml
  configuration:
    #开启驼峰命名规则 比如数据库字段是有下划线的t_no,那么代码中就要写成Tno代码里面自动把下划线的字母变成大写
    map-underscore-to-camel-case: true
    type-aliases-package: com.o2o.data


# 开启日志
logging:
  level:
    com:
      o2o:
        cy: debug

创建实体类book对象
@Data注解自动实现setter和getter方法

创建接口统一返回类和枚举类

创建mapper层getBookList方法

package com.o2o.mapper;

import com.o2o.data.Book;
import com.o2o.data.param.BookParams;

import java.util.List;

/**
 * @Time : 2022/12/27 18:25
 * @Author : wcy
 * @FileName:
 * @email :954515472@qq.com
 */

public interface BookMapper {
    List<Book> getBookList(BookParams bookParams);
}

创建service层getBookList方法

package com.o2o.service;

import com.o2o.data.Book;
import com.o2o.data.param.BookParams;

import java.util.List;

/**
 * @Time : 2022/12/27 18:14
 * @Author : wcy
 * @FileName:
 * @email :954515472@qq.com
 */

public interface BookService {
    /**
     * 按照查询条件分页查询书籍
     */
    List<Book> getBookList(BookParams bookParams);
}

创建serviceImpl实现类
在service层中通过 @Resource注解注入mapper ，就可以直接通过mapper对象调用mapper接口中定义的方法，mapper中的方法名 与mapper.xml中的名字一一对应

package com.o2o.service.impl;

import com.o2o.data.Book;
import com.o2o.data.param.BookParams;
import com.o2o.mapper.BookMapper;
import com.o2o.service.BookService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

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

/**
 * @Time : 2022/12/27 18:27
 * @Author : wcy
 * @FileName:
 * @email :954515472@qq.com
 */

@Service
public class BookServiceImpl implements BookService {

    @Resource
    private BookMapper bookMapper;

    @Override
    public List<Book> getBookList(BookParams bookParams) {
       return bookMapper.getBookList(bookParams);
    }

    @Override
    public Long getTotalCount(BookParams bookParams) {
        return bookMapper.getTotalCount(bookParams);
    }
}

创建controller层接收前端传入的参数

• @Resource注解注入service层对象
• public返回的是一个CommonResponse对象，因为我们查询全部getBookLists(BookParams bookParams)传了参，映射一个GetMapping请求方法，传入路径名“/getBookLists”
• @ResponseBody注解将controller层的方法返回结果写入到响应正文response对象的body中，直接返回JSON数据

package com.o2o.controller;

import com.o2o.common.CommonResponse;
import com.o2o.data.Book;
import com.o2o.data.param.BookParams;
import com.o2o.service.BookService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

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

/**
 * @Time : 2022/12/27 18:04
 * @Author : wcy
 * @FileName:
 * @email :954515472@qq.com
 */

@RestController
@RequestMapping("book")
public class BookController {

    @Resource
    private BookService bookService;
    /**
     * 按照条件获取书籍信息
     * @param bookParams
     * @return
     */
    @GetMapping("/getBookLists")
    @ResponseBody //@ResponseBody注解将controller层的方法返回结果写入到响应正文response对象的body中，直接返回JSON数据
    public CommonResponse<List<Book>> getBookLists(BookParams bookParams) {
        // 按照查询条件分页查询书籍
        List<Book> books = bookService.getBookList(bookParams);
        CommonResponse response = CommonResponse.successInstance(books);
        return response;
    }
}

启动run
我们可以看到springboot已经运行成功啦

在浏览器输入{ip}+路径访问

到这里就大功告成啦！