java集成easyexcel的使用（一）（导出，包含跨行合并，别名的功能，包含完整工具类）

1、前言

阿里的easyexcel性能比poi是要好很多，不会出现oom的问题。但是官方文档的说明太少，本人工作中遇到类似跨行合并导出的这种业务，花了一点时间研究出来，现整理在博客中。

2、导出

一、maven引用

 
            com.alibaba
            easyexcel
            2.0.0
 

二、集成工具类

public class EasyExcelUtil {

    /**
     * 动态列
     */
    public static void writeExcel(HttpServletResponse response, String fileName,String sheetName, Map keyMap, List data,String ...defaultValue) throws Exception {
        response.setContentType("application/vnd.ms-excel");
        response.setCharacterEncoding("utf-8");
        response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName.replaceAll("\\+", "_"), "UTF-8"));

        writeExcel(response.getOutputStream(), fileName, sheetName, keyMap, data, defaultValue);
    }
    public static void writeExcel(HttpServletResponse response, String fileName,String sheetName, Map keyMap, List data,List writeHandler,String ...defaultValue) throws Exception {
        response.setContentType("application/vnd.ms-excel");
        response.setCharacterEncoding("utf-8");
        response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName.replaceAll("\\+", "_"), "UTF-8"));

        writeExcel(response.getOutputStream(), fileName, sheetName, keyMap, data,writeHandler,defaultValue);
    }

    /**
     * 动态列
     */
    public static void writeExcel(OutputStream outputStream,
                                  String fileName,
                                  String sheetName,
                                  Map keyMap,
                                  List data,
                                  String ...defaultValue) throws Exception {
        writeExcel(outputStream, fileName, sheetName, keyMap, data, null, defaultValue);
    }

    /**
     * 动态列
     */
    public static void writeExcel(OutputStream outputStream,
                                  String fileName,
                                  String sheetName,
                                  Map keyMap,
                                  List data,
                                  List writeHandler,
                                  String ...defaultValue) throws Exception {
        if(!(keyMap instanceof LinkedHashMap)){
            throw new IllegalArgumentException("key map should be LinkedHashMap");
        }

        List> header = new ArrayList<>();
        for (Object key : keyMap.values()) {
            if (Collection.class.isAssignableFrom(key.getClass())) {
                List heads = new ArrayList<>();
                for (Object o : (Collection) key) {
                    heads.add(o.toString());
                }
                header.add(heads);
            } else {
                header.add(Lists.newArrayList(key.toString()));
            }
        }

        List> listData = new ArrayList<>();
        try {
            Class clazz = null;
            Field[] fields = null;

            for (Object datum : data) {
                if (clazz == null) {
                    clazz = datum.getClass();
                    fields = clazz.getDeclaredFields();
                }

                List