Java实现导入、导出、处理Excel文件

一、内容概述

在实际开发中，难以避免遇到对Excel文件导入、导出的需求，由于我是第一次做便在此做学习记录，目的在于加深印象，便于回顾。本文将使用到POI技术处理包、java反射机制实现导入前端上传导入Excel文件，后端读取信息并将信息封装入实体对象；反过来，实现把实体对象的属性信息以Excel文件导出。最后将功能封装成工具类，便于复用。

二、主要内容

1.创建一个简单的Spring boot 项目

1.1写一个简单Controller返回测试页面

@Controller
public class TestController {
   @RequestMapping(value = "/upload",method = RequestMethod.GET)
   public String upload(){
       return "upload";
   }

}

1.2前端页面

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form action="/upload" method="post" enctype="multipart/form-data" onsubmit="return void(0)">
    <input type="file" name="file" id="file">
    <button type="submit">上传</button>
</form>
<a href="/download">导出</a>
</body>
</html>

一个简单的报表和一个导出按钮，报表用于上传Excel文件。

2.导包

        <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>

PS:如果在运行时出现java.lang.ClassNotFoundException: org.apache.poi.xssf.usermodel.XSSFWorkbook异常，多半为poi包与poi-ooxml包的版本不匹配造成，若检查版本没有问题，可以选择注释掉poi让maven自动导入poi依赖。

此外还需导入工具包：

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-collections4</artifactId>
            <version>4.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.9</version>
        </dependency>

3.创建自定义注解

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ExcelColumn {
    String value() default "";
    int col() default 0;
}

4.创建实体类，并加自定义注解

import com.guohui.demo_poi.annotation.ExcelColumn;
public class Student {
    @ExcelColumn(value = "学号",col = 1)
    private Long studentId;
    @ExcelColumn(value = "姓名",col = 2)
    private String name;
    @ExcelColumn(value = "性别",col = 3)
    private String sex;
    @ExcelColumn(value = "班级",col = 4)
    private String grade; 

    @Override
    public String toString() {
        return "Student{" +
                "studentId=" + studentId +
                ", name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", grade='" + grade + '\'' +
                '}';
    }
    public Student(){
    }
    public Long getStudentId() {
        return studentId;
    }
    public void setStudentId(Long studentId) {
        this.studentId = studentId;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getGrade() {
        return grade;
    }
    public void setGrade(String grade) {
        this.grade = grade;
    }
}

value值需与Excel表头列名对应，导入Excel进行数据封装时以此对应关系进行赋值。多个注解value可以相同，赋值时会一并赋值。
col值为列索引，导出Excel文件时以col值从小到大向右排列。

5.创建ExcelUtils工具类

import com.guohui.demo_poi.annotation.ExcelColumn;
import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.lang3.BooleanUtils;
import org.apache.commons.lang3.CharUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.math.NumberUtils;
import org.apache.poi.hssf.usermodel.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.MediaType;
import org.springframework.web.multipart.MultipartFile;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.math.BigDecimal;
import java.net.URLEncoder;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class ExcelUtils {
    private final static Logger log = LoggerFactory.getLogger(ExcelUtils.class);
    private final static String EXCEL2003 = "xls";
    private final static String EXCEL2007 = "xlsx";

    /**
     * 读取EXCEL文件
     * @param cls 封装对象类类型
     * @param file 前端上传的MultipartFile对象
     * @param <T> 封装对象类型
     * @return T对象集合
     */
    public static <T> List<T> readExcel(Class<T> cls,MultipartFile file){

        String fileName = file.getOriginalFilename(); //获取上传文件名
        if (!fileName.matches("^.+\\.(?i)(xls)$") && !fileName.matches("^.+\\.(?i)(xlsx)$")) {
            log.error("上传文件格式不正确");
        }
        List<T> dataList = new ArrayList<>();
        Workbook workbook = null;
        try {
            InputStream is = file.getInputStream();
            if (fileName.endsWith(EXCEL2007)) {
//                FileInputStream is = new FileInputStream(new File(path));
                workbook = new XSSFWorkbook(is);
            }
            if (fileName.endsWith(EXCEL2003)) {
//                FileInputStream is = new FileInputStream(new File(path));
                workbook = new HSSFWorkbook(is);
            }

            if (workbook != null) {
                //类映射  注解 value-->bean columns（注解value可能相同，并注释多个字段）
                Map<String, List<Field>> classMap = new HashMap<>();
                //获取字段集合
                List<Field> fields = Stream.of(cls.getDeclaredFields()).collect(Collectors.toList());
                //遍历字段集合
                fields.forEach(
                        field -> {
                            //过滤未加ExcelColumn的字段
                            ExcelColumn annotation = field.getAnnotation(ExcelColumn.class);
                            if (annotation != null) {
                                //获取注解值
                                String annotationValue = annotation.value();
                                if (StringUtils.isBlank(annotationValue)) {
                                    //过滤注解value为空的字段
                                    return;//return起到的作用和continue是相同的语法
                                }
                                //若注解value未存在则添加映射
                                if (!classMap.containsKey(annotationValue)) {
                                    classMap.put(annotationValue, new ArrayList<>());
                                }
                                //开启字段访问权限
                                field.setAccessible(true);
                                classMap.get(annotationValue).add(field);
                            }
                        }
                );
                //索引-->columns
                Map<Integer, List<Field>> reflectionMap = new HashMap<>(16);
                //默认读取第一个sheet
                Sheet sheet = workbook.getSheetAt(0);

                boolean firstRow = true;
                //遍历行
                for (int i = sheet.getFirstRowNum(); i <= sheet.getLastRowNum(); i++) {
                    Row row = sheet.getRow(i);
                    //首行  提取注解(列名)
                    if (firstRow) {
                        //遍历列
                        for (int j = row.getFirstCellNum(); j <= row.getLastCellNum(); j++) {
                            Cell cell = row.getCell(j);
                            String columnName = getCellValue(cell);
                            if (classMap.containsKey(columnName)) {
                                //以列名为key获取对应的封装字段集合
                                reflectionMap.put(j, classMap.get(columnName));
                            }
                        }
                        firstRow = false;
                    } else {
                        //忽略空白行
                        if (row == null) {
                            continue;
                        }
                        try {
                            //反射创建封装对象
                            T t = cls.newInstance();
                            //是否为空白单元格
                            boolean cellBlank = true;
                            //遍历列
                            for (int j = row.getFirstCellNum(); j <= row.getLastCellNum(); j++) {
                                if (reflectionMap.containsKey(j)) {
                                    Cell cell = row.getCell(j);
                                    String cellValue = getCellValue(cell);
                                    if (StringUtils.isNotBlank(cellValue)) {
                                        cellBlank = false;
                                    }
                                    //通过列索引获取字段集合
                                    List<Field> fieldList = reflectionMap.get(j);
                                    //遍历字段集合，利用反射机制循环封装数据
                                    fieldList.forEach(
                                            x -> {
                                                try {
                                                    handleField(t, cellValue, x);
                                                } catch (Exception e) {
                                                    log.error(String.format("反射写入异常！字段名:%s 值:%s ", x.getName(), cellValue), e);
                                                }
                                            }
                                    );
                                }
                            }
                            //若单元不全为空，则保存封装对象
                            if (!cellBlank) {
                                dataList.add(t);
                            } else {
                                log.warn(String.format("第%s行为空，已忽略!", i));
                            }
                        } catch (Exception e) {
                            log.error(String.format("解析第%s行异常！", i), e);
                        }
                    }
                }
            }
        } catch (Exception e) {
            log.error(String.format("解析excel文件异常!"), e);
        } finally {
            if (workbook != null) {
                try {
                    workbook.close();
                } catch (Exception e) {
                    log.error(String.format("解析excel文件异常!"), e);
                }
            }
        }
        return dataList;
    }

    /**
     * 反射写入属性
     * @param t
     * @param value
     * @param field
     * @param <T>
     * @throws Exception
     */
    private static <T> void handleField(T t, String value, Field field) throws Exception {
        //获取字段类型
        Class<?> type = field.getType();
        if (type == null || type == void.class || StringUtils.isBlank(value)) {
            return;
        }
        if (type == Object.class) {
            field.set(t, value);
            //数字类型
        } else if (type.getSuperclass() == null || type.getSuperclass() == Number.class) {
            if (type == int.class || type == Integer.class) {
                field.set(t, NumberUtils.toInt(value));
            } else if (type == long.class || type == Long.class) {
                field.set(t, NumberUtils.toLong(value));
            } else if (type == byte.class || type == Byte.class) {
                field.set(t, NumberUtils.toByte(value));
            } else if (type == short.class || type == Short.class) {
                field.set(t, NumberUtils.toShort(value));
            } else if (type == double.class || type == Double.class) {
                field.set(t, NumberUtils.toDouble(value));
            } else if (type == float.class || type == Float.class) {
                field.set(t, NumberUtils.toFloat(value));
            } else if (type == char.class || type == Character.class) {
                field.set(t, CharUtils.toChar(value));
            } else if (type == boolean.class) {
                field.set(t, BooleanUtils.toBoolean(value));
            } else if (type == BigDecimal.class) {
                field.set(t, new BigDecimal(value));
            }
        } else if (type == Boolean.class) {
            field.set(t, BooleanUtils.toBoolean(value));
        } else if (type == Date.class) {
            //
            field.set(t, value);
        } else if (type == String.class) {
            field.set(t, value);
        } else {
            Constructor<?> constructor = type.getConstructor(String.class);
            field.set(t, constructor.newInstance(value));
        }
    }

    /**
     * 获取单元格内容
     * @param cell
     * @return
     */
    private static String getCellValue(Cell cell) {
        if (cell == null) {
            return "";
        }
        if (cell.getCellTypeEnum() == CellType.NUMERIC) {
            if (DateUtil.isCellDateFormatted(cell)) {
                return HSSFDateUtil.getJavaDate(cell.getNumericCellValue()).toString();
            } else {
                return new BigDecimal(cell.getNumericCellValue()).toString();
            }
        } else if (cell.getCellTypeEnum() == CellType.STRING) {
            return StringUtils.trimToEmpty(cell.getStringCellValue());
        } else if (cell.getCellTypeEnum() == CellType.FORMULA) {
            return StringUtils.trimToEmpty(cell.getCellFormula());
        } else if (cell.getCellTypeEnum() == CellType.BLANK) {
            return "";
        } else if (cell.getCellTypeEnum() == CellType.BOOLEAN) {
            return String.valueOf(cell.getBooleanCellValue());
        } else if (cell.getCellTypeEnum() == CellType.ERROR) {
            return "ERROR";
        } else {
            return cell.toString().trim();
        }

    }

    /**
     * 生成excel对应的Workbook对象
     * @param dataList 对象集合
     * @param cls   对象类类型
     * @param <T>  对象类型
     * @return Workbook对象
     */
    public static <T> Workbook writeExcel(List<T> dataList, Class<T> cls){
        //获取字段集合
        Field[] fields = cls.getDeclaredFields();
        //过滤没有ExcelColumn注解的字段，并排序
        List<Field> fieldList = Arrays.stream(fields)
                .filter(field -> {
                    ExcelColumn annotation = field.getAnnotation(ExcelColumn.class);
                    if (annotation != null && annotation.col() > 0) {
                        field.setAccessible(true);
                        return true;
                    }
                    return false;
                }).sorted(Comparator.comparing(field -> {
                    int col = 0;
                    ExcelColumn annotation = field.getAnnotation(ExcelColumn.class);
                    if (annotation != null) {
                        col = annotation.col();
                    }
                    return col;
                })).collect(Collectors.toList());
        //创建工作页
        Workbook wb = new XSSFWorkbook();
        //新建工作页
        Sheet sheet = wb.createSheet("Sheet1");
        //创建线程安全的AtomicInteger，默认为0
        AtomicInteger ai = new AtomicInteger();


        {
            Row headRow = sheet.createRow(ai.getAndIncrement());
            
            AtomicInteger aj = new AtomicInteger();
            //写入头部
            fieldList.forEach(field -> {
                ExcelColumn annotation = field.getAnnotation(ExcelColumn.class);
                String columnName = "";
                if (annotation != null) {
                    columnName = annotation.value();
                }
                //创建标题行
                Cell cell = headRow.createCell(aj.getAndIncrement());
                //设置格式
                CellStyle cellStyle = wb.createCellStyle();
                cellStyle.setFillForegroundColor(IndexedColors.WHITE.getIndex());
                cellStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
                cellStyle.setAlignment(HorizontalAlignment.CENTER);
                //设置字体
                Font font = wb.createFont();
                font.setBold(true);

                //应用格式与字体
                cellStyle.setFont(font);
                cell.setCellStyle(cellStyle);
                cell.setCellValue(columnName);
            });
        }

        //写入内容
        if (CollectionUtils.isNotEmpty(dataList)) {
            dataList.forEach(object -> {
                Row contentRow = sheet.createRow(ai.getAndIncrement());
                AtomicInteger aj = new AtomicInteger();
                fieldList.forEach(field -> {
                    Class<?> type = field.getType();
                    Object value = "";
                    try {
                        value = field.get(object);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }

                    Cell cell = contentRow.createCell(aj.getAndIncrement());
                    if (value != null) {
                        if (type == Date.class) {
                            cell.setCellValue(value.toString());
                        } else {
                            cell.setCellValue(value.toString());
                        }
                        cell.setCellValue(value.toString());
                    }
                });
            });
        }
        //冻结窗格
        wb.getSheet("Sheet1").createFreezePane(0, 1, 0, 1);
        return wb;
    }

    /**
     * 浏览器下载excel
     * @param fileName
     * @param wb
     * @param response
     */

    public static  void  buildExcelDocument(String fileName, Workbook wb,HttpServletResponse response){
        try {
            response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
            response.setHeader("Content-Disposition", "attachment;filename="+URLEncoder.encode(fileName, "utf-8"));
            response.flushBuffer();
            wb.write(response.getOutputStream());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 生成excel文件
     * @param path 生成excel路径
     * @param wb
     */
    private static  void  buildExcelFile(String path, Workbook wb){

        File file = new File(path);
        if (file.exists()) {
            file.delete();
        }
        try {
            wb.write(new FileOutputStream(file));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

本想自己写一个封装工具类，但发现一位大佬博主已经写好了（原网站在之后给出），我在此基础上进行了一些简单的修改（poi版本不一样），并根据自己的理解做了一些注释，改善代码的可读性。

5.1值得注意问题的问题

数据格式问题
取值前应先判断单元格的数据格式，再按对应数据格式进行取值，否则报错。
poi支持6种类型，并且每种类型都定义了类型常量：

poi支持的类型

图中为poi 3.15版本之前的调用方式，3.15之后的调用方法可见工具类，但支持的类型还是一样的。

6.增加Controller方法

   @ResponseBody
    @RequestMapping(value = "/upload",method = RequestMethod.POST)
    public String doUpload(MultipartFile file) throws Exception {
        if (file != null){
            System.out.println(file.getOriginalFilename());
        }else {
            System.out.println("空");
        }
        List<Student> students = ExcelUtils.readExcel(Student.class, file);
        students.forEach(student -> {
            System.out.println(student.toString());
        });

        return "OK";
    }

    @RequestMapping(value = "/download")
    public void download(HttpServletResponse response) throws IOException {
        //创建测试数据
        List<Student> studentList = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            Student student = new Student();
            student.setStudentId(Long.valueOf(i+1));
            student.setName("测试"+i);
            student.setSex("男"+i);
            student.setGrade("大班"+i);
            studentList.add(student);
        }

        Workbook workbook = ExcelUtils.writeExcel(studentList, Student.class);
        ExcelUtils.buildExcelDocument("test.xlsx",workbook,response);

    }

doUpload方法用于接收前端表单上传的Excel文件，调用ExcelUtils类readExcel方法进行数据读取并封装。
download方法为前端导出Excel文件的处理方法。
测试Excel如下：

测试Excel

7.运行测试

1.上传Excel文件输出

image.png

2.导出文件输出