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EasyExcel

官方文档

EasyExcel官方文档 - 基于Java的Excel处理工具 | Easy Excel (alibaba.com)

优势

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。一旦并发上来后一定会OOM或者JVM频繁的full gc.
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。

代码示例

关于Easyexcel | Easy Excel (alibaba.com)

excel转json数据

引入easy excel依赖

        <!-- easy excel -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>easyexcel</artifactId>
            <version>3.3.2</version>
        </dependency>

编写controller

package com.junfeng.tool.controller;

import com.alibaba.excel.EasyExcel;
import com.alibaba.fastjson.JSON;
import com.github.xiaoymin.knife4j.annotations.ApiOperationSupport;
import com.github.xiaoymin.knife4j.annotations.ApiSupport;
import com.junfeng.tool.config.EasyExcelListener;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

import java.io.IOException;
import java.util.List;
import java.util.Map;

/***
 * @Author junfeng
 */
@Api(tags = "excel")
@ApiSupport(author = "1033110136@qq.com", order = 1)
@RestController
@RequestMapping("/api/excel")
@Slf4j
public class  ExcelController {


    @ApiOperationSupport(author = "junfeng")
    @ApiOperation(value = "excel转换json")
    @PostMapping("/upload")
    public Object upload(@RequestParam("file") MultipartFile file) throws IOException {
        // 读取Excel
        EasyExcel.read(file.getInputStream(), new EasyExcelListener()).sheet().headRowNumber(1).doRead();

        // 从监听中获取结果集
        List<Map<String, Object>> importList = EasyExcelListener.dataList;
        log.info("导入集合 list = {}", JSON.toJSON(importList));

        return JSON.toJSON(importList);
    }


}

监听器

package com.junfeng.tool.config;

import com.alibaba.excel.context.AnalysisContext;
import com.alibaba.excel.event.AnalysisEventListener;
import lombok.extern.slf4j.Slf4j;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@Slf4j
public class EasyExcelListener extends AnalysisEventListener<Map<String, Object>> {

    private Map<Integer, String> headMap;

    public static final List<Map<String, Object>> dataList = new ArrayList<>();

    @Override
    public void invoke(Map<String, Object> data, AnalysisContext context) {
        //把表头和值放入Map
        HashMap<String, Object> paramsMap = new HashMap<>();
        for (int i = 0; i < data.size(); i++) {
            String key = headMap.get(i);
            Object value = data.get(i);
            //将表头作为map的key每行每个单元格的数据作为map的value
            paramsMap.put(key, value);
            dataList.add(paramsMap);
        }
    }

    @Override
    public void doAfterAllAnalysed(AnalysisContext context) {

    }

    @Override
    public void invokeHeadMap(Map<Integer, String> head, AnalysisContext context) {
        headMap = head;
    }


}

重点代码解析

public abstract class AnalysisEventListener<T> implements ReadListener<T> {
    public AnalysisEventListener() {
    }

    public void invokeHead(Map<Integer, ReadCellData<?>> headMap, AnalysisContext context) {
        this.invokeHeadMap(ConverterUtils.convertToStringMap(headMap, context), context);
    }

    public void invokeHeadMap(Map<Integer, String> headMap, AnalysisContext context) {
    }
}

public interface ReadListener<T> extends Listener {
    default void onException(Exception exception, AnalysisContext context) throws Exception {
        throw exception;
    }

    default void invokeHead(Map<Integer, ReadCellData<?>> headMap, AnalysisContext context) {
    }

    void invoke(T var1, AnalysisContext var2);

    default void extra(CellExtra extra, AnalysisContext context) {
    }

    void doAfterAllAnalysed(AnalysisContext var1);

    default boolean hasNext(AnalysisContext context) {
        return true;
    }
}