踹掉后端，前端导出Excel！

　　前言

　　导出Excel文件这个功能，通常都是在后端实现返回前端一个下载链接，但有时候我们只想导出前端页面上已经有了的数据，不想再调后端导出接口浪费服务器资源，学习本文demo例子，我们踹掉后端，直接在前端导出Excel！

　　代码实现

　　1、利用Blob对象构造一个a标签的href链接，从而实现文件下载，Excel支持html格式，因此我们只需要将构造好的html内容放到Blob对象中，即可下载Excel表格

　　2、利用base64编码构造一个a标签的href链接，从而实现文件下载，同上，我们需要将构造好的html内容URI编码拼到base64链接，即可下载Excel表格

    //blob、base64转文件下载，通过A标签模拟点击,设置文件名
    /*
        万能流  application/octet-stream
        word文件  application/msword
        excel文件  application/vnd.ms-excel
        txt文件  text/plain
        图片文件  image/png、jpeg、gif、bmp
     */
    function downloadByBlob(fileName, text) {
        let a = document.createElement("a");
        a.href = URL.createObjectURL(new Blob([text], {type: "application/octet-stream"}));
        a.download = fileName || 'Blob导出测试.txt';
        a.click();
        a.remove();
        URL.revokeObjectURL(a.href);
    }
    function downloadByBase64(fileName, text) {
        let a = document.createElement('a');
        a.href = 'data:application/octet-stream;base64,' + window.btoa(unescape(encodeURIComponent(text)));
        a.download = fileName || 'Base64导出测试.txt';
        a.click();
        a.remove();
        URL.revokeObjectURL(a.href);
    }

　　封装导出Excel表格方法

    //踹掉后端，前端导出Excel！
    function exportExcel(fileName,columns,datas){
        //列名
        let columnHtml = "";
        columnHtml += "\n";
        for (let key in columns) {
            columnHtml += ""+columns[key]+"\n";
        }
        columnHtml += "\n";

        //数据
        let dataHtml = "";
        for (let data of datas) {
            dataHtml += "\n";
            for (let key in columns) {
                dataHtml += ""+data[key]+"\n";
            }
            dataHtml += "\n";
        }

        //完整html
        let excelHtml = "\n" +
            "\n" +
            "   " +
            "   \n" +
            "        \n" +
            "            \n" +
            "                \n" +
            "                    \n" +
            "                    \n" +
            "                        \n" +
            "                    \n" +
            "                \n" +
            "            \n" +
            "        \n" +
            "   \n" +
            "   \n" +
            "\n" +
            "\n" +
            "\n" +
            "    \n" +
            columnHtml +
            "    \n" +
            "    \n" +
            dataHtml +
            "    \n" +
            "\n" +
            "\n" +
            "";

        //下载
        downloadByBlob((fileName || "导出Excel")+".xls",excelHtml);
    }

　　效果演示

　　导出txt文档

downloadByBlob("downloadByBlob-导出txt文档.txt","downloadByBlob\n导出txt简单测试\n");
downloadByBase64("downloadByBase64-导出txt文档.txt","downloadByBase64\n导出txt简单测试\n");

　　导出Excel表格

exportExcel("xx业务Excel导出", {"id": "编号", "name": "名字", "age": "年龄", "time": "参加工作时间"}, [{
            "id": "A001",
            "name": "张三",
            "age": "18",
            "time": new Date().toLocaleString()
        },{
            "id": "A002",
            "name": "李四",
            "age": "20",
            "time": new Date().toLocaleString()
        }]);

　　导出word文档也是一样

　　后记

　　参考上我们之前的《》，先画好我们想要的文档格式然后转成xml，调用我们封装好的方法，将构造好的xml内容转成文件，实现前端导出复杂格式文档！

　　如果有复杂数据，建议还是在后端操作，当然你也可以把数据返回前端在前端导出也行

　　前端导出Excel主要是利用Bolb、base64，以及Excel支持html格式的特性，这个特性不仅前端可以利用，后端也一样可以，这里也分享一下后端工具类，原理都是一样的

package cn.huanzi.qch.util;

import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.*;

/**
 * Excel工具类
 */
public class ExcelUtil {

    /**
     * 导出
     * 无需依赖POI
     */
    /*
        示例：
        try {
            //列名
            LinkedHashMap columns = new LinkedHashMap<>(4);
            columns.put("id","编号");
            columns.put("name","名字");
            columns.put("age","年龄");
            columns.put("time","参加工作时间");

            //数据
            List> datas = new ArrayList<>(3);
            HashMap hashMap = new HashMap<>();
            hashMap.put("id","A001");
            hashMap.put("name","张三");
            hashMap.put("age",18);
            hashMap.put("time",new Date());
            datas.add(hashMap);

            //带换行符：

            HashMap hashMap2 = new HashMap<>();
            hashMap2.put("id","A002");
            hashMap2.put("name","李四
李四1
李四2");
            hashMap2.put("age",20);
            hashMap2.put("time",new Date());
            datas.add(hashMap2);

            HashMap hashMap3 = new HashMap<>();
            hashMap3.put("id","A003");
            hashMap3.put("name","王五");
            hashMap3.put("age",25);
            hashMap3.put("time",new Date());
            datas.add(hashMap3);

            //导出
            ExcelUtil.exportByResponse(this.getResponse(),"Excel导出测试",columns,datas);
            //ExcelUtil.exportByFile(new File("D:\\XFT User\\Downloads\\Excel导出测试.xls"),columns,datas);
        } catch (Exception e) {
            e.printStackTrace();
        }
     */
    public static void exportByResponse(HttpServletResponse response, String fileName, LinkedHashMap columns, List> datas) throws Exception {
        response.addHeader("Content-disposition", "attachment; filename=" + fileName + ".xls");
        response.setContentType("application/ms-excel");

        StringBuilder sb = exportOfData(columns, datas);

        OutputStream out = response.getOutputStream();
        out.write(sb.toString().getBytes("UTF-8"));
        out.flush();
        out.close();
    }

    public static void exportByFile(File file, LinkedHashMap columns, List> datas) {
        StringBuilder sb = exportOfData(columns, datas);

        try (PrintWriter myFile = new PrintWriter(file,"UTF-8")) {
            myFile.println(sb);
        } catch (Exception e) {
            System.err.println("exportByFile()，操作出错...");
            e.printStackTrace();
        }
        System.out.println(file.getName() + "，操作完成！");
    }

    //其他单元格无边框
    private static StringBuilder exportOfData(LinkedHashMap columns, List> datas) {
        StringBuilder sb = new StringBuilder("");

        //加这个，其他单元格带边框
        sb.append("" +
                "    " +
                "        " +
                "            " +
                "                " +
                "                    " +
                "                    " +
                "                        " +
                "                    " +
                "                " +
                "            " +
                "        " +
                "    " +
                "   " +
                "");

        sb.append("");

        sb.append("");

        //列名
        sb.append("");
        for (Map.Entry entry : columns.entrySet()) {
            sb.append("");
        }
        sb.append("");

        //数据for (Map data : datas) {
            sb.append("");
            for (Map.Entry entry : columns.entrySet()) {
                Object dataValue = data.get(entry.getKey());

                //如果是日期类型
                if (dataValue instanceof java.util.Date) {
                    dataValue = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(dataValue);
                }
                sb.append("");
            }
            sb.append("");
        }

        sb.append("
" + entry.getValue() + "
        
" + dataValue.toString() + "
");

        sb.append("");

        sb.append("");

        return sb;
    }

    //前端导出Excel
    /*
        示例：
         exportExcel("xx业务Excel导出", {"id": "编号", "name": "名字", "age": "年龄", "time": "参加工作时间"}, [{
            "id": "A001",
            "name": "张三",
            "age": "18",
            "time": new Date().toLocaleString()
        },{
            "id": "A002",
            "name": "李四",
            "age": "20",
            "time": new Date().toLocaleString()
        }]);
     */
    /*
        //blob、base64转文件下载，通过A标签模拟点击,设置文件名
        //万能流  application/octet-stream
        //word文件  application/msword
        //excel文件  application/vnd.ms-excel
        //txt文件  text/plain
        //图片文件  image/png、jpeg、gif、bmp
        function downloadByBlob(fileName, text) {
            let a = document.createElement("a");
            a.href = URL.createObjectURL(new Blob([text], {type: "application/octet-stream"}));
            a.download = fileName || 'Blob导出测试.txt';
            a.click();
            a.remove();
            URL.revokeObjectURL(a.href);
        }
        function downloadByBase64(fileName, text) {
            let a = document.createElement('a');
            a.href = 'data:application/octet-stream;base64,' + window.btoa(unescape(encodeURIComponent(text)));
            a.download = fileName || 'Base64导出测试.txt';
            a.click();
            a.remove();
            URL.revokeObjectURL(a.href);
        }
    
        //踹掉后端，前端导出Excel！
        function exportExcel(fileName,columns,datas){
            //列名
            let columnHtml = "";
            columnHtml += "\n";
            for (let key in columns) {
                columnHtml += ""+columns[key]+"\n";
            }
            columnHtml += "\n";
    
            //数据
            let dataHtml = "";
            for (let data of datas) {
                dataHtml += "\n";
                for (let key in columns) {
                    dataHtml += ""+data[key]+"\n";
                }
                dataHtml += "\n";
            }
    
            //完整html
            let excelHtml = "http://www.w3.org/TR/REC-html40\">\n" +
                    "\n" +
                    "   " +
                    "   \n" +
                    "        \n" +
                    "            \n" +
                    "                \n" +
                    "                    \n" +
                    "                    \n" +
                    "                        \n" +
                    "                    \n" +
                    "                \n" +
                    "            \n" +
                    "        \n" +
                    "   \n" +
                    "   \n" +
                    "\n" +
                    "\n" +
                    "\n" +
                    "    \n" +
                    columnHtml +
                    "    \n" +
                    "    \n" +
                    dataHtml +
                    "    \n" +
                    "\n" +
                    "\n" +
                    "";
    
            //下载
            downloadByBlob((fileName || "导出Excel")+".xls",excelHtml);
        }
     */
}