引入

为什么使用EasyExcel?

Java解析、生成Excel比较有名的框架有Apache poi、jxl。但他们都存在一个严重的问题就是非常的耗内存，poi有一套SAX模式的API可以一定程度的解决一些内存溢出的问题，但POI还是有一些缺陷，比如07版Excel解压缩以及解压后存储都是在内存中完成的，内存消耗依然很大。

EasyExcel重写了poi对07版Excel的解析，一个3M的excel用POI sax解析依然需要100M左右内存，改用EasyExcel可以降低到几M，并且再大的excel也不会出现内存溢出；03版依赖POI的sax模式，在上层做了模型转换的封装，让使用者更加简单方便。

官网GitHub地址：

https://github.com/alibaba/easyexcel

官方文档地址：

https://www.yuque.com/easyexcel/doc/easyexcel

实例

创建初始数据

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `user_id` bigint(20) NULL DEFAULT NULL,
  `username` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `phone` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `create_time` date NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 2 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES (1, 1, 'banq', '13588888888', '2021-11-19');

SET FOREIGN_KEY_CHECKS = 1;

创建SpringBoot项目

导入EasyExcel依赖

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>easyexcel</artifactId>
    <version>2.2.10</version>
</dependency>

User

@Data
public class User {
    @ExcelIgnore  //生成报表时忽略
    private Long id;

    @ExcelProperty(value = "用户ID",index = 0)  // 定义表头名称和位置,0代表第一列
    private Long userId;

    @ExcelProperty(value = "用户名称",index = 1)
    private String username;

    @ExcelProperty(value = "电话号码",index = 2)
    private String phone;

    @ExcelProperty(value = "创建日期",index = 3)
    @DateTimeFormat("yyyy年MM月dd日")
    private Date createTime;
}

监听器

@Slf4j
public class UserDataListener extends AnalysisEventListener<User> {

    private UserService userService;

    public UserDataListener(UserService userService) {
        this.userService = userService;
    }

    /**
     * 每隔5条存储数据库，实际使用中可以3000条，然后清理list ，方便内存回收
     */
    private static final int BATCH_COUNT = 5;
    List<User> list = new ArrayList<User>();

    @Override
    public void invoke(User data, AnalysisContext context) {
        log.info("解析到一条数据:{}", JSON.toJSONString(data));
        list.add(data);
        if (list.size() >= BATCH_COUNT) {
            saveData();
            list.clear();
        }
    }

    @Override
    public void doAfterAllAnalysed(AnalysisContext context) {
        saveData();
        log.info("所有数据解析完成！");
    }

    /**
     * 加上存储数据库
     */
    private void saveData() {
        log.info("{}条数据，开始存储数据库！", list.size());
        if (!CollectionUtils.isEmpty(list)) {
            userService.saveBatch(list);
        }
        log.info("存储数据库成功！");
    }
}

Dao层

@Mapper
@Repository
public interface UserMapper {
    void batchInsert(List<User> list);
    List<User> queryAll();
}

<insert id="batchInsert">
    insert into user (user_id,username,phone,create_time) values
    <foreach collection="list" item="user" separator=",">
        (#{user.userId},#{user.username},#{user.phone},#{user.createTime})
    </foreach>
</insert>
<select id="queryAll" resultType="ink.banq.demo.entity.User">
    select id,user_id,username,phone,create_time from user
</select>

Service层

public interface UserService {
    void saveBatch(List<User> list);
    List<User> selectAll();
}

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private UserMapper userMapper;

    @Override
    public void saveBatch(List<User> list) {
        userMapper.batchInsert(list);
    }

    @Override
    public List<User> selectAll() {
        return userMapper.queryAll();
    }
}

Controller层

@RestController
public class OperateExcelController {
    @Autowired
    private UserService userService;

    /**
     * 上传文件
     * @param file
     * @return
     * @throws IOException
     */
    @PostMapping("upload")
    @ResponseBody
    public String upload(MultipartFile file) throws IOException {
        EasyExcel.read(file.getInputStream(), User.class, new UserDataListener(userService)).sheet().doRead();
        return "success";
    }

    /**
     * 导出文件
     * @param response
     * @throws IOException
     */
    @GetMapping("download")
    public void download(HttpServletResponse response) throws IOException {
        // 设置上下文类型
        response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
        // 设置编码
        response.setCharacterEncoding("utf-8");
        // 防止中文乱码
        String fileName = URLEncoder.encode("文件名称", "UTF-8").replaceAll("\\+", "%20");
        response.setHeader("Content-disposition", "attachment;filename*=utf-8''" + fileName + ".xlsx");
        EasyExcel.write(response.getOutputStream()).sheet("模板").doWrite(userService.selectAll());
    }

}

测试

（1）测试导入功能，使用Postman测试，如下图所示：

1.jpg

（2）测试导出功能，浏览器访问：http://localhost:8080/download

2.jpg