EasyExcel的用法

一.Excel导入导出的应用场景

1.数据导入：减轻录入的工作量

2.数据导出：统计信息归档

3.数据传输：异构系统之间数据传输

二。EasyExcel简介

1.EasyExcel特点

Java领域解析，生成Excel比较有名的框架有Apache poi,jxl等，但他们都存在一个严重的问题就是非常的耗内存，如果你的系统并发量不大的话可能还行，但是一旦并发上来后一定会OOM或者JVM频繁的full gc.

EasyExcel是阿里巴巴开源的一个excel处理框架，以使用简单，节省内存著称，EasyExcel能大大减少占用内存的主要原因是在解析Excel时没有将文件数据一次性全部加载到内存中，而是从磁盘上一行行读取数据，逐个解析。

EasyExcel采用一行一行的解析模式，并将一行的解析结果以观察者的模式通知处理（AnalysisEventListener）。

1.导入maven依赖，主要还需要poi的依赖，并且版本要对应上

<!-- https://mvnrepository.com/artifact/com.alibaba/easyexcel -->
<dependency>
　　<groupId>com.alibaba</groupId>
　　<artifactId>easyexcel</artifactId>
　　<version>2.1.1</version>
</dependency>

<!--xls-->
<dependency>
　　<groupId>org.apache.poi</groupId>
　　<artifactId>poi</artifactId>
　　<version>3.17</version>
</dependency>
<dependency>
　　<groupId>org.apache.poi</groupId>
　　<artifactId>poi-ooxml</artifactId>
　　<version>3.17</version>
</dependency>

2.编写entity对象类

@Data
public class DemoData {
    //设置excel表头名称
    @ExcelProperty(value = "学生编号",index = 0)
    private Integer sno;
    @ExcelProperty(value = "学生姓名",index = 1)
    private String sname;
}

3.写操作

public class TestEasyExcelWrite {

    public static void main(String[] args) {

        //实现excel写的操作
        //1 设置写入文件夹地址和excel文件名称
        String filename = "C:\Users\aus\write.xlsx";
       // 2 调用easyexcel里面的方法实现写操作
       // write方法两个参数：第一个参数文件路径名称，第二个参数实体类class
        EasyExcel.write(filename,DemoData.class).sheet("学生列表").doWrite(getData());

    }

    //创建方法返回list集合
    private static List<DemoData> getData() {
        List<DemoData> list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            DemoData data = new DemoData();
            data.setSno(i);
            data.setSname("lucy"+i);
            list.add(data);
        }
        return list;
    }
}

4.最终效果 

 5.读取excel需要先写一个监听器继承AnalysisEventListener

public class ExcelListener extends AnalysisEventListener<DemoData> {
    //一行一行读取excel内容
    @Override
    public void invoke(DemoData data, AnalysisContext analysisContext) {
        System.out.println("****"+data);
    }
    //读取表头内容
    @Override
    public void invokeHeadMap(Map<Integer, String> headMap, AnalysisContext context) {
        System.out.println("表头："+headMap);
    }
    //读取完成之后
    @Override
    public void doAfterAllAnalysed(AnalysisContext analysisContext) { }
}

6.读取excel代码

public class TestEasyExcelRead {

    public static void main(String[] args) {

        //实现excel读操作
        String filename = "C:\Users\aus\write.xlsx";
        EasyExcel.read(filename,DemoData.class,new ExcelListener()).sheet().doRead();
    }
}

打印效果见下图：

---

实际项目中开发

entity

@Data
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
@ApiModel(value="EduSubject对象", description="课程科目")
public class EduSubject implements Serializable {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "课程类别ID")
    @TableId(value = "id", type = IdType.ID_WORKER_STR)
    private String id;

    @ApiModelProperty(value = "类别名称")
    private String title;

    @ApiModelProperty(value = "父ID")
    private String parentId;

    @ApiModelProperty(value = "排序字段")
    private Integer sort;

    @ApiModelProperty(value = "创建时间")
    @TableField(fill = FieldFill.INSERT)
    private Date gmtCreate;

    @ApiModelProperty(value = "更新时间")
    @TableField(fill = FieldFill.INSERT)
    private Date gmtModified;
    
}

@Data
public class SubjectData {
    @ExcelProperty(index = 0)
    private String oneSubjectName;
    @ExcelProperty(index = 1)
    private String twoSubjectName;
}

Controller层

@RestController
@RequestMapping("/eduservice/subject")
@CrossOrigin
public class EduSubjectController {


    @Autowired
    private EduSubjectService subjectService;

    //添加课程分类
    //获取上传过来文件，把文件内容读取出来
    @PostMapping("addSubject")
    public R addSubject(MultipartFile file) {
        //上传过来excel文件
        subjectService.saveSubject(file,subjectService);
        return R.ok();
    }

}

service层

@Service
public class EduSubjectServiceImpl extends ServiceImpl<EduSubjectMapper, EduSubject> implements EduSubjectService {

    @Override
    public void saveSubject(MultipartFile file, EduSubjectService subjectService) {

        try{
            InputStream in = file.getInputStream();
            EasyExcel.read(in, SubjectData.class,new SubjectExcelListener(subjectService)).sheet().doRead();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

 5.监听器继承AnalysisEventListener，这里需要注意的点，因为业务层的SubjectExcelListener 并没有交给Spring容器来管理，所以监听器代码无法注入EduSubjectService ，

这里通过构造方法的方式传过来，从而完成对数据库的操作。

public class SubjectExcelListener extends AnalysisEventListener<SubjectData> {

    //因为SubjectExcelListener不交给spring进行管理，需要自己new，不能注入其他对象
    //不能实现数据库操作
    public EduSubjectService subjectService;
    public SubjectExcelListener() {}
    public SubjectExcelListener(EduSubjectService subjectService) {
        this.subjectService = subjectService;
    }

    //读取excel内容，一行一行进行读取
    @Override
    public void invoke(SubjectData subjectData, AnalysisContext analysisContext) {
        if(subjectData == null) {
            throw new GuliException(20001,"文件数据为空");
        }

        //一行一行读取，每次读取有两个值，第一个值一级分类，第二个值二级分类
        //判断一级分类是否重复
        EduSubject existOneSubject = this.existOneSubject(subjectService, subjectData.getOneSubjectName());
        if(existOneSubject == null) { //没有相同一级分类，进行添加
            existOneSubject = new EduSubject();
            existOneSubject.setParentId("0");
            existOneSubject.setTitle(subjectData.getOneSubjectName());//一级分类名称
            subjectService.save(existOneSubject);
        }

        //获取一级分类id值
        String pid = existOneSubject.getId();

        //添加二级分类
        //判断二级分类是否重复
        EduSubject existTwoSubject = this.existTwoSubject(subjectService, subjectData.getTwoSubjectName(), pid);
        if(existTwoSubject == null) {
            existTwoSubject = new EduSubject();
            existTwoSubject.setParentId(pid);
            existTwoSubject.setTitle(subjectData.getTwoSubjectName());//二级分类名称
            subjectService.save(existTwoSubject);
        }
    }

    //判断一级分类不能重复添加
    private EduSubject existOneSubject(EduSubjectService subjectService,String name) {
        QueryWrapper<EduSubject> wrapper = new QueryWrapper<>();
        wrapper.eq("title",name);
        wrapper.eq("parent_id","0");
        EduSubject oneSubject = subjectService.getOne(wrapper);
        return oneSubject;
    }

    //判断二级分类不能重复添加
    private EduSubject existTwoSubject(EduSubjectService subjectService,String name,String pid) {
        QueryWrapper<EduSubject> wrapper = new QueryWrapper<>();
        wrapper.eq("title",name);
        wrapper.eq("parent_id",pid);
        EduSubject twoSubject = subjectService.getOne(wrapper);
        return twoSubject;
    }

    @Override
    public void doAfterAllAnalysed(AnalysisContext analysisContext) {

    }
}