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ExcelEasyExcel.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<>();@Overridepublic void invoke(Map<String, Object> data, AnalysisContext context) {//把表头和值放入MapHashMap<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valueparamsMap.put(key, value);dataList.add(paramsMap);}}@Overridepublic void doAfterAllAnalysed(AnalysisContext context) {}@Overridepublic 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;}
}