【EasyExcel实践】万能导出，一个接口导出多张表以及任意字段（可指定字段顺序）

前言

日前，看到一个比较奇怪的导出功能。

需要根据不同的页面，以及指定不同的字段列表（任意顺序），然后导出对应的表格。

先假设一个场景：
假如你的系统有多个列表展示页，每页中可以依据筛选条件，调整展示的列的个数，顺序等。然后要求导出的时侯，导出一摸一样的格式。也就是“所见即所得”的表格。

那么基于以上场景，我们就来考虑下如何实现？
本文就是对以上场景功能的一个实现。目前仅支持单sheet，不支持数据聚合等。

正文

本文项目环境：
java 8，springboot2.2.0, easyexcel

一、POM依赖

<dependencies>
    <dependency>
        <groupId&gt;org.springframework.boot</groupId&gt;
        <artifactId&gt;spring-boot-starter-web</artifactId>
        <version>2.2.0.RELEASE</version>
    </dependency>

    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.2</version>
    </dependency>


    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>easyexcel</artifactId>
        <version>2.2.11</version>

        <exclusions>
            <exclusion>
                <groupId>org.slf4j</groupId>
                <artifactId>slf4j-api</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

</dependencies>

二、核心Java文件

此处粘贴全部的java文件

2.1 自定义表头注解 ExcelColumnTitle

package headbean;

import java.lang.annotation.*;

/**
 * 列名标题注解，标注列的标题
 *
 * @author feng
 */
@Documented
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface ExcelColumnTitle {
    String value();
}

2.2 自定义标题头的映射接口

此接口仅仅是用于规范实体，以及用于辅助实现导出功能。

package headbean;

/**
 * excel头部映射接口，用于规范导出的实体类
 *
 * @author feng
 */
public interface ExcelHeadMapInterface {
}

2.3 自定义有序map存储表内数据

这个是表格导出时，字段数量，顺序的关键。

package headbean;

import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

/**
 * 表格数据专用的map，带顺序，而且初始化的时候，依据指定的表头变量字段名确定导出数据的顺序
 *
 * @author feng
 */
public class ExcelDataLinkedHashMap<V> extends LinkedHashMap<String, V> {

    private static final long serialVersionUID = -8554095999151235982L;

    /**
     * 头部字段名缓存
     */
    private final Set<String> headColumnNamesCache;

    /**
     * ExcelDataLinkedHashMap构造器
     *
     * @param headColumnNames 表头字段变量名，例如：[name,studentNo,age,className]
     */
    public ExcelDataLinkedHashMap(List<String> headColumnNames) {
        // 字段名去重
        headColumnNames = headColumnNames.stream().distinct().collect(Collectors.toList());
        // 构建字段名缓存
        this.headColumnNamesCache = new HashSet<>(headColumnNames);
        // 指定列数据排列顺序
        for (String headColumnName : headColumnNames) {
            this.put(headColumnName, null);
        }
    }

    @Override
    public V put(String key, V value) {
        // 只保存字段名缓存中的key以及value
        if (headColumnNamesCache.contains(key)) {
            return super.put(key, value);
        }
        return null;
    }
}

2.4 表头工厂

负责实现初始化表头字段名，以及后期使用时，从中获取表头信息。
核心功能是解析自定义的表头注解。

package factory;

import enums.ExcelHeadBeanFlagEnum;
import headbean.ExcelColumnTitle;
import headbean.ExcelHeadMapInterface;

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;


public class ExcelHeadMapFactory {
    /**
     * 全局表头名映射，ExcelHeadMapInterface实现类型为key，它内部变量的变量名和中文名映射为value
     */
    private static final Map<Class<? extends ExcelHeadMapInterface>, Map<String, String>> HEAD_NAME_MAP = new HashMap<>();

    public static void addHeadClass(Class<? extends ExcelHeadMapInterface> headClass) {
        HEAD_NAME_MAP.put(headClass, mapToPrepareHead(headClass));
    }

    public static Map<String, String> getHeadMap(Class<? extends ExcelHeadMapInterface> headClass) {
        return HEAD_NAME_MAP.get(headClass);
    }

    public static Map<String, String> getHeadMapByFlag(String flag) {
        return getHeadMap(ExcelHeadBeanFlagEnum.getHeadClass(flag));
    }

    private static Map<String, String> mapToPrepareHead(Class<?> excelHeadClass) {
        Map<String, String> namedMap = new HashMap<>();
        Field[] declaredFields = excelHeadClass.getDeclaredFields();
        for (Field declaredField : declaredFields) {
            boolean annotationPresent = declaredField.isAnnotationPresent(ExcelColumnTitle.class);
            if(annotationPresent) {
                ExcelColumnTitle excelProperty = declaredField.getAnnotation(ExcelColumnTitle.class);
                String chineseFieldName = excelProperty.value();
                // 保存字段名和中文变量名
                namedMap.put(declaredField.getName(), chineseFieldName);
            }
        }

        return namedMap;
    }
}

2.5 表flag和表头映射枚举

这个枚举，如果你的系统这类功能很多。可以设计为数据库的方式做映射。然后以查字典表的方式，来处理。当然使用枚举大概率是够用了。

package enums;

import headbean.ExcelHeadMapInterface;
import headbean.NameAndFactoryDemo;
import headbean.StudentDemo;
import lombok.AllArgsConstructor;
import lombok.Getter;

import java.util.Arrays;

/**
 * 表头flag枚举，映射flag与对应的实体类型；主要是可以根据flag找到对应实体类型。
 *
 * @author feng
 */
@Getter
@AllArgsConstructor
public enum ExcelHeadBeanFlagEnum {

    NAME_AND_FACTORY_DEMO("NameAndFactoryDemo", NameAndFactoryDemo.class),
    STUDENT_DEMO("StudentDemo", StudentDemo.class)
    ;

    private final String flag;
    private final Class<? extends ExcelHeadMapInterface> headClass;

    public static Class<? extends ExcelHeadMapInterface> getHeadClass(String flag) {
        return Arrays.stream(values()).
                filter(bean -> bean.getFlag().equals(flag))
                .findFirst()
                .orElseThrow(RuntimeException::new)
                .getHeadClass();
    }
}

2.6 测试用的实体

2.6.1 NameAndFactoryDemo

package headbean;

import lombok.Data;

@Data
public class NameAndFactoryDemo implements ExcelHeadMapInterface {
    @ExcelColumnTitle("名字")
    private String name;
    @ExcelColumnTitle("工厂")
    private String factory;
}

2.6.2 StudentDemo

package headbean;

import lombok.Data;

@Data
public class StudentDemo implements ExcelHeadMapInterface {
    @ExcelColumnTitle("姓名")
    private String name;
    @ExcelColumnTitle("年龄")
    private Integer age;
    @ExcelColumnTitle("学号")
    private String studentNo;
    @ExcelColumnTitle("班级")
    private String className;
}

2.7 启动类

主要是项目启动后，注册表头数据到内存。

package org.feng;

import factory.ExcelHeadMapFactory;
import headbean.ExcelHeadMapInterface;
import headbean.NameAndFactoryDemo;
import headbean.StudentDemo;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import java.util.ArrayList;
import java.util.List;

@SpringBootApplication
public class ExcelDemoApplication implements CommandLineRunner {

    public static void main(String[] args) {
        SpringApplication.run(ExcelDemoApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        List<Class<? extends ExcelHeadMapInterface>> needRegisterExcelHeadClassList = new ArrayList<>();
        needRegisterExcelHeadClassList.add(NameAndFactoryDemo.class);
        needRegisterExcelHeadClassList.add(StudentDemo.class);
        needRegisterExcelHeadClassList.forEach(ExcelHeadMapFactory::addHeadClass);
    }
}

2.8 测试控制器

package org.feng;

import com.alibaba.excel.EasyExcel;
import com.alibaba.excel.write.metadata.WriteSheet;
import enums.ExcelHeadBeanFlagEnum;
import factory.ExcelHeadMapFactory;
import headbean.ExcelDataLinkedHashMap;
import headbean.ExcelHeadMapInterface;
import headbean.NameAndFactoryDemo;
import headbean.StudentDemo;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

import javax.annotation.PostConstruct;
import javax.servlet.http.HttpServletResponse;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.*;
import java.util.function.BiFunction;

@Controller
@RequestMapping("/excel")
public class ExcelDemoController {

    @GetMapping("/exportDy")
    public String exportDy(@RequestParam("flag")String flag,
                           @RequestParam("table")List<String> table, HttpServletResponse response) throws IOException {
        String fileName = System.currentTimeMillis() + ".xlsx";

        Class<? extends ExcelHeadMapInterface> headClass = ExcelHeadBeanFlagEnum.getHeadClass(flag);
        Map<String, String> namedPrepareHeadMap = ExcelHeadMapFactory.getHeadMap(headClass);
        Map<String, String> head = new LinkedHashMap<>();
        for (String fieldName : table) {
            head.put(namedPrepareHeadMap.get(fieldName), fieldName);
        }

        List<Map<String, String>> excelDataList = new ArrayList<>();
        excelDataList.add(head);

        // 制造假数据
        for (BiFunction<Class<? extends ExcelHeadMapInterface>, List<Map<String, String>>, Boolean> biFunction : bizList) {
            Boolean applied = biFunction.apply(headClass, excelDataList);
            if(applied) {
                break;
            }
        }

        byte[] bytes = easyOut(excelDataList);
        response.setHeader("Content-disposition", "attachment;filename=" + fileName);
        response.setContentType("application/x-msdownload");
        response.setCharacterEncoding("utf-8");
        response.getOutputStream().write(bytes);
        response.getOutputStream().flush();

        return "success";
    }

    static final List<BiFunction<Class<? extends ExcelHeadMapInterface>, List<Map<String, String>>, Boolean>> bizList = new ArrayList<>();

    @PostConstruct
    private void init() {
        bizList.add(this::genStudentDemoData);
        bizList.add(this::genNameAndFactoryDemoData);
    }


    private boolean genStudentDemoData(Class<? extends ExcelHeadMapInterface> headClass, List<Map<String, String>> excelDataList) {
        if(headClass == StudentDemo.class) {
            Map<String, String> headMap = excelDataList.get(0);
            for (int i = 0; i < 5; i++) {
                Collection<String> fieldNames = headMap.values();
                Map<String, String> data = new ExcelDataLinkedHashMap<>(new ArrayList<>(fieldNames));
                excelDataList.add(data);
                data.put("name", "张三"+(i+1));
                data.put("age", "年龄"+(i+1));
                data.put("studentNo", "学号"+(i+1));
                data.put("className", "班级"+(i+1));
            }
            return true;
        }
        return false;
    }

    private boolean genNameAndFactoryDemoData(Class<? extends ExcelHeadMapInterface> headClass, List<Map<String, String>> excelDataList) {
        if(headClass == NameAndFactoryDemo.class) {
            Map<String, String> headMap = excelDataList.get(0);
            for (int i = 0; i < 5; i++) {
                Collection<String> fieldNames = headMap.values();
                Map<String, String> data = new ExcelDataLinkedHashMap<>(new ArrayList<>(fieldNames));
                excelDataList.add(data);
                data.put("name", "张三"+(i+1));
                data.put("factory", "工厂"+(i+1));
            }
            return true;
        }
        return false;
    }



    /**
     * 导出数据（单sheet）
     * @param exportData key 是sheet名称，value是每个sheet里面的数据，支持自定义表头
     */
    public static byte[] easyOut(List<Map<String, String>> exportData) {
        return easyOut(Collections.singletonMap("Sheet", exportData));
    }

    /**
     * 导出数据（多sheet）
     * @param exportData key 是sheet名称，value是每个sheet里面的数据，可以自定义
     */
    public static byte[] easyOut(Map<String, List<Map<String, String>>> exportData) {
        // 导出数据
        ByteArrayOutputStream out = new ByteArrayOutputStream();

        com.alibaba.excel.ExcelWriter excelWriter = EasyExcel.write(out).build();
        int i=0;
        for (Map.Entry<String, List<Map<String, String>>> entry: exportData.entrySet()) {
            WriteSheet writeSheet = EasyExcel.writerSheet(i, entry.getKey()).head(head(entry.getValue().get(0))).build();
            i++;
            excelWriter.write(data(entry.getValue(), true), writeSheet);
        }
        excelWriter.finish();

        return out.toByteArray();
    }

    private static List<List<String>> head(Map<String, String> cellData) {
        List<List<String>> head = new ArrayList<>();
        for (String key: cellData.keySet()) {
            head.add(Collections.singletonList(key));
        }
        return head;
    }

    private static List<List<String>> data(List<Map<String, String>> sheetData, boolean skipHead) {
        List<List<String>> data = new ArrayList<>();
        for (int i = 0; i < sheetData.size(); i++) {
            if(i == 0 &amp;&amp; skipHead) {
                continue;
            }
            data.add(new ArrayList<>(sheetData.get(i).values()));
        }
        return data;
    }
}

三、测试

测试1

http://localhost:8080/excel/exportDy?flag=StudentDemo&table=name,studentNo,age,className

获得的表格内容为：

测试2

http://localhost:8080/excel/exportDy?flag=StudentDemo&table=name,studentNo,age

获得的表格内容为：

测试3

http://localhost:8080/excel/exportDy?flag=NameAndFactoryDemo&table=factory,name
获得的表格内容为：

测试4

http://localhost:8080/excel/exportDy?flag=StudentDemo&table=className,name,studentNo
获得的表格内容为：

代码007普通

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