springboot+mybatis实现数据分页(三种方式)

项目准备

1.创建用户表

2.使用spring初始化向导快速创建项目，勾选mybatis，web，jdbc，driver
添加lombok插件

<?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 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>2.4.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.hao</groupId>
    <artifactId>spring-boot-crud-end</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>spring-boot-crud-end</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.4</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

---

一、使用原生Java实现分页

1.UserMapper接口

@Mapper
@Repository
public interface UserMapper {
    int selectCount();
    List<User> selectUserFindAll();
}

2.整合mybatis（application.yaml)

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/crud?serverTimezone=UTC
    username: root
    password: hao20001010
mybatis:
  mapper-locations: classpath:mapper/*.xml
  type-aliases-package: com.hao.springboot.entity

3.测试dao层(成功）

@SpringBootTest
class SpringBootCrudEndApplicationTests {
    @Autowired
    UserMapper userMapper;
    @Test
    void contextLoads() {
        List<User> users = userMapper.selectUserFindAll();
        for(User user:users){
            System.out.println(user);
        }
    }
    @Test
    void contextLoads2(){
    }
}

4.编写service层

public interface UserService {
    int selectCount();
    List<User> selectUserByArray(int currentPage,int pageSize);
}

/**
 * @author:抱着鱼睡觉的喵喵
 * @date:2020/12/26
 * @description:
 */
@Service
public class UserServiceImpl implements UserService {
    @Autowired
    UserMapper userMapper;
    @Override
    public int selectCount() {
        int count = userMapper.selectCount();
        return count;
    }
    /**
     * 原始分页逻辑实现
     * @param currentPage	当前页
     * @param pageSize		每页的数量
     * @return
     */
    @Override
    public List<User> selectUserByArray(int currentPage, int pageSize) {
        List<User> users = userMapper.selectUserFindAll();
        int count=selectCount();
        int startCurrentPage=(currentPage-1)*pageSize;        //开启的数据
        int endCurrentPage=currentPage*pageSize;        //结束的数据
        int totalPage=count/pageSize;                   //总页数
        if (currentPage>totalPage || currentPage<=0){
            return null;
        }else{
            return users.subList(startCurrentPage,endCurrentPage);
        }
    }
}

5.controller层

@RestController
public class UserController {
    @Autowired
    UserService userService;
    @GetMapping("/user/{currentPage}/{pageSize}")
    public List<User> selectFindPart(@PathVariable("currentPage") int currentPage, @PathVariable("pageSize") int pageSize){
        List<User> list = userService.selectUserByArray(currentPage, pageSize);
        if (list==null){
            throw new UserNotExistException("访问出错!QWQ");
        }else{
            return list;
        }
    }
}

6.异常处理

public class UserNotExistException extends RuntimeException{
    private static final long serialVersionUID = 1L;
    private String msg;
    public UserNotExistException(String msg) {
        super("user not exist");
        this.msg=msg;
    }
    public String getMsg() {
        return msg;
    }
    public void setMsg(String msg) {
        this.msg = msg;
    }
}

7.controller异常处理类

/**
 * @author:抱着鱼睡觉的喵喵
 * @date:2020/12/26
 * @description:
 */
@ControllerAdvice			//处理controller层出现的异常
public class ControllerExceptionHandler {
    @ExceptionHandler(UserNotExistException.class)
    @ResponseBody
    @ResponseStatus(value = HttpStatus.INTERNAL_SERVER_ERROR) //状态码
    public Map<String,Object> handlerUserNotExistException(UserNotExistException ex){
        Map<String,Object> result=new HashMap<>();
        result.put("msg", ex.getMsg());
        result.put("message", ex.getMessage());
        return result;
    }
}

8.访问http://localhost:8080/user/5/10出现如下

{“msg”:“访问出错!QWQ”,“message”:“user not exist”}

9.访问http://localhost:8080/user/2/3 出现如下

[{“id”:4,“userName”:“sky”,“password”:“789”},{“id”:5,“userName”:“nulls”,“password”:“tom”},{“id”:6,“userName”:“zsh”,“password”:“zsh”}]

总结:
缺点：数据库查询并返回所有的数据，而我们需要的只是极少数符合要求的数据。当数据量少时，还可以接受。当数据库数据量过大时，每次查询对数据库和程序的性能都会产生极大的影响。

---

二、通过sql语句进行分页操作

1.在UserMapper接口中新增一个方法

@Mapper
@Repository
public interface UserMapper {
//原生分页
    int selectCount();
    List<User> selectUserFindAll();
//通过sql语句进行分页
    List<User> selectBySql(Map<String,Object> map);
}

2.UserService接口中新增方法，以及UserServiceImpl类中进行重写

public interface UserService {
    int selectCount();
    /**
     * 原生分页
     * @param currentPage
     * @param pageSize
     * @return
     */
    List<User> selectUserByArray(int currentPage,int pageSize);
    /**
     * 通过sql分页
     * @param currentPage
     * @param pageSize
     * @return
     */
    List<User> selectUserBySql(int currentPage,int pageSize);
}

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    UserMapper userMapper;
    @Override
    public int selectCount() {
        int count = userMapper.selectCount();
        return count;
    }
    /**
     * 原始分页逻辑实现
     * @param currentPage
     * @param pageSize
     * @return
     */
    @Override
    public List<User> selectUserByArray(int currentPage, int pageSize) {
        List<User> users = userMapper.selectUserFindAll();
        int count=selectCount();
        int startCurrentPage=(currentPage-1)*pageSize;        //从第几个数据开始
        int endCurrentPage=currentPage*pageSize;        //结束的数据
        int totalPage=count/pageSize;                   //总页数
        if (currentPage>totalPage || currentPage<=0){
            return null;
        }else{
            return users.subList(startCurrentPage,endCurrentPage);
        }
    }
/**
*通过sql语句进行分页
*/
    @Override
    public List<User> selectUserBySql(int currentPage, int pageSize) {
        Map<String,Object> map=new HashMap<>();
        int startCurrentPage=(currentPage-1)*pageSize;        //从第几个数据开始
        int count=selectCount();
        int totalPage=count/pageSize;                   //总页数
        if (currentPage>totalPage || currentPage<=0){
            return null;
        }else{
            map.put("currentPage",startCurrentPage);
            map.put("pageSize",pageSize);
            List<User> list = userMapper.selectBySql(map);
            return list;
        }
    }
}

3.controller层编写

@RestController
public class UserController {
    @Autowired
    UserService userService;
//Java原生实现分页模块
    @GetMapping("/user/{currentPage}/{pageSize}")
    public List<User> selectFindByJava(@PathVariable("currentPage") int currentPage, @PathVariable("pageSize") int pageSize){
        List<User> list = userService.selectUserByArray(currentPage, pageSize);
        if (list==null){
            throw new UserNotExistException("访问出错!QWQ");
        }else{
            return list;
        }
    }
//sql分页方法模块
    @GetMapping("/user2/{currentPage}/{pageSize}")
    public List<User> selectFindBySql(@PathVariable("currentPage") int currentPage, @PathVariable("pageSize") int pageSize){
        List<User> list = userService.selectUserBySql(currentPage,pageSize);
        if (list==null){
            throw new UserNotExistException("访问出错!QWQ");
        }else{
            return list;
        }
    }
}

4.UserMapper.xml添加查询条件，使用limit进行分页

<?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.hao.springboot.mapper.UserMapper">
    <resultMap id="user" type="com.hao.springboot.entity.User">
        <result column="user_name" property="userName"/>
        <result column="password" property="password"/>
    </resultMap>
    <select id="selectUserFindAll" resultMap="user">
        select * from user
    </select>
    <select id="selectCount" resultType="integer">
        select count(*) from user
    </select>
    <select id="selectBySql" parameterType="map" resultType="com.hao.springboot.entity.User">
        select * from user limit #{currentPage} , #{pageSize}
    </select>
</mapper>

5.启动访问http://localhost:8080/user2/5/10 出现如下

{“msg”:“访问出错!QWQ”,“message”:“user not exist”}

接着正确访问http://localhost:8080/user2/2/2

[{“id”:3,“userName”:“tom”,“password”:“456”},{“id”:4,“userName”:“sky”,“password”:“789”}]

总结：
缺点：虽然这里实现了按需查找，每次检索得到的是指定的数据。但是每次在分页的时候都需要去编写limit语句，很冗余。而且不方便统一管理，维护性较差。所以我们希望能够有一种更方便的分页实现。

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三、拦截器实现分页