最近在工作中遇到一个需求，就是需要在前端实现一个错误模板Excel的下载功能。
实现下载有两种方式，一种是后端生成一个excel，放在服务器指定目录下，然后前端直接去后端拿。第二种是后端传给前端一个json的list，前端用后端传过来的json的list直接在前端合成一个excel。
第一种：后端生成excel
java后端生成excel代码
生成excel工具方法
/** * @author: wu linchun * @creat: 2021-07-29 9:49 * @desc: 将list集合转成Excel文件 * list: 内容list * path: 上传的excel路径 * fileName: 上传的excel名称 **/public static String createExcel(List<? extends Object> list, String path, String fileName) {String result = "";if (list.size() == 0 || list == null) {result = "没有对象信息";} else {Object o = list.get(0);Class<? extends Object> clazz = o.getClass();String className = clazz.getSimpleName();//这里通过反射获取字段数组Field[] fields = clazz.getDeclaredFields();File folder = new File(path);if (!folder.exists()) {folder.mkdirs();}String name = fileName.concat(".xls");WritableWorkbook book = null;File file = null;try {file = new File(path.concat(File.separator).concat(name));//创建xls文件book = jxl.Workbook.createWorkbook(file);WritableSheet sheet = book.createSheet(className, 0);//列int i = 0;//行int j = 0;for (Field f : fields) {j = 0;//这里把字段名称写入excel第一行中Label label = new Label(i, j, f.getName());sheet.addCell(label);j = 1;for (Object obj : list) {Object temp = getFieldValueByName(f.getName(), obj);String strTemp = "";if (temp != null) {strTemp = temp.toString();}//把每个对象此字段的属性写入这一列excel中sheet.addCell(new Label(i, j, strTemp));j++;}i++;}book.write();result = file.getPath();} catch (Exception e) {// TODO Auto-generated catch blockresult = "SystemException";e.printStackTrace();} finally {fileName = null;name = null;folder = null;file = null;if (book != null) {try {book.close();} catch (WriteException e) {// TODO Auto-generated catch blockresult = "WriteException";e.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blockresult = "IOException";e.printStackTrace();}}}}//最后输出文件路径return result;}
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下载文件
/** * @author: wu linchun * @creat: 2021-07-29 13:28 * @desc: 下载错误模板 **/@Overridepublic ResponseEntity<Object> downloadErrorModel() throws FileNotFoundException {// 这里的fileName是指路径+文件名String fileName="move_cms/src/main/resources/static/errorList.xls";File file = new File(fileName);InputStreamResource resource = new InputStreamResource(new FileInputStream((file)));org.springframework.http.HttpHeaders headers = new org.springframework.http.HttpHeaders();headers.add("Content-Disposition", String.format("attachment;filename="%s"", file.getName()));headers.add("Cache-Control", "no-cache,no-store,must-revalidate");headers.add("Pragma", "no-cache");headers.add("Expires", "0");ResponseEntity<Object> responseEntity = ResponseEntity.ok().headers(headers).contentLength(file.length()).contentType(MediaType.parseMediaType("application/text")).body(resource);return responseEntity;}
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下载excel的接口
/** * @author: wu linchun * @creat: 2021-07-29 11:41 * @desc: 下载错误模板 **/@ApiOperation(value = "下载错误模板")@GetMapping(value = "/downloadErrorModel")@PassTokenpublic ResponseEntity<Object> downloadErrorModel() throws FileNotFoundException {System.out.println("下载错误模板");return welfareGrantService.downloadErrorModel();}
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在掉/downloadErrorModel这个接口是要注意，只能用超链接 “<a:href />调用，不能使用axios调这个接口。这是由于axios获取的是json
而这个接口返回的是file类型，file会以byte流的形式在http上面传输，因此调/downloadErrorModel这个接口将会接收到byte流，axios默认是接收不了byte的，需要进行一些特殊的设置。可以参考一下这篇：vue使用axios接收流文件_weixin_43869439的博客-CSDN博客
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如果使用超链接的方式访问接口进行文件下载的话，则需要获取到后端服务器的ip+port （实际中不建议这么做，因为get请求会暴露ip地址和端口，可通过浏览器f12看到ip地址和端口，不安全）
ip地址可通过 InetAddress.getLocalHost()获取到，端口号直接用@Value从配置文件中拿到。
第二种：前端合成excel
在vue工程中引入两个依赖：file-saver和xlsx
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使用“npm install”，安装package.json中新增的依赖
npm install
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新增 ExportExcelUtil.js，用来根据list生成excel
/* eslint-disable */
import { saveAs } from 'file-saver'
import XLSX from 'xlsx'
function generateArray(table) {var out = [];var rows = table.querySelectorAll('tr');var ranges = [];for (var R = 0; R < rows.length; ++R) {var outRow = [];var row = rows[R];var columns = row.querySelectorAll('td');for (var C = 0; C < columns.length; ++C) {var cell = columns[C];var colspan = cell.getAttribute('colspan');var rowspan = cell.getAttribute('rowspan');var cellValue = cell.innerText;if (cellValue !== "" && cellValue == +cellValue) cellValue = +cellValue;//Skip rangesranges.forEach(function (range) {if (R >= range.s.r && R <= range.e.r && outRow.length >= range.s.c && outRow.length <= range.e.c) {for (var i = 0; i <= range.e.c - range.s.c; ++i) outRow.push(null);}});//Handle Row Spanif (rowspan || colspan) {rowspan = rowspan || 1;colspan = colspan || 1;ranges.push({s: {r: R,c: outRow.length},e: {r: R + rowspan - 1,c: outRow.length + colspan - 1}});};//Handle ValueoutRow.push(cellValue !== "" ? cellValue : null);//Handle Colspanif (colspan)for (var k = 0; k < colspan - 1; ++k) outRow.push(null);}out.push(outRow);}return [out, ranges];
};
function datenum(v, date1904) {if (date1904) v += 1462;var epoch = Date.parse(v);return (epoch - new Date(Date.UTC(1899, 11, 30))) / (24 * 60 * 60 * 1000);
}
function sheet_from_array_of_arrays(data, opts) {var ws = {};var range = {s: {c: 10000000,r: 10000000},e: {c: 0,r: 0}};for (var R = 0; R != data.length; ++R) {for (var C = 0; C != data[R].length; ++C) {if (range.s.r > R) range.s.r = R;if (range.s.c > C) range.s.c = C;if (range.e.r < R) range.e.r = R;if (range.e.c < C) range.e.c = C;var cell = {v: data[R][C]};if (cell.v == null) continue;var cell_ref = XLSX.utils.encode_cell({c: C,r: R});if (typeof cell.v === 'number') cell.t = 'n';else if (typeof cell.v === 'boolean') cell.t = 'b';else if (cell.v instanceof Date) {cell.t = 'n';cell.z = XLSX.SSF._table[14];cell.v = datenum(cell.v);} else cell.t = 's';ws[cell_ref] = cell;}}if (range.s.c < 10000000) ws['!ref'] = XLSX.utils.encode_range(range);return ws;
}
function Workbook() {if (!(this instanceof Workbook)) return new Workbook();this.SheetNames = [];this.Sheets = {};
}
function s2ab(s) {var buf = new ArrayBuffer(s.length);var view = new Uint8Array(buf);for (var i = 0; i != s.length; ++i) view[i] = s.charCodeAt(i) & 0xFF;return buf;
}
export function export_table_to_excel(id) {var theTable = document.getElementById(id);var oo = generateArray(theTable);var ranges = oo[1];/* original data */var data = oo[0];var ws_name = "SheetJS";var wb = new Workbook(),ws = sheet_from_array_of_arrays(data);/* add ranges to worksheet */// ws['!cols'] = ['apple', 'banan'];ws['!merges'] = ranges;/* add worksheet to workbook */wb.SheetNames.push(ws_name);wb.Sheets[ws_name] = ws;var wbout = XLSX.write(wb, {bookType: 'xlsx',bookSST: false,type: 'binary'});saveAs(new Blob([s2ab(wbout)], {type: "application/octet-stream"}), "test.xlsx")
}
export function export_json_to_excel({multiHeader = [],header,data,filename,merges = [],autoWidth = true,bookType = 'xlsx'
} = {}) {/* original data */filename = filename || 'excel-list'data = [...data]data.unshift(header);for (let i = multiHeader.length - 1; i > -1; i--) {data.unshift(multiHeader[i])}var ws_name = "SheetJS";var wb = new Workbook(),ws = sheet_from_array_of_arrays(data);if (merges.length > 0) {if (!ws['!merges']) ws['!merges'] = [];merges.forEach(item => {ws['!merges'].push(XLSX.utils.decode_range(item))})}if (autoWidth) {/*设置worksheet每列的最大宽度*/const colWidth = data.map(row => row.map(val => {/*先判断是否为null/undefined*/if (val == null) {return {'wch': 10};}/*再判断是否为中文*/else if (val.toString().charCodeAt(0) > 255) {return {'wch': val.toString().length * 2};} else {return {'wch': val.toString().length};}}))/*以第一行为初始值*/let result = colWidth[0];for (let i = 1; i < colWidth.length; i++) {for (let j = 0; j < colWidth[i].length; j++) {if (result[j]['wch'] < colWidth[i][j]['wch']) {result[j]['wch'] = colWidth[i][j]['wch'];}}}ws['!cols'] = result;}/* add worksheet to workbook */wb.SheetNames.push(ws_name);wb.Sheets[ws_name] = ws;var wbout = XLSX.write(wb, {bookType: bookType,bookSST: false,type: 'binary'});saveAs(new Blob([s2ab(wbout)], {type: "application/octet-stream"}), `${filename}.${bookType}`);
}
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在.vue中添加下载excel方法
// 下载ExceldownloadExcel () {import('@/utils/ExportExcelUtil').then(excel => {const filterVal = ['item', 'error']const tHeader = ['item', 'error']const data = this.formatModelJson(filterVal, this.errList)console.log(data)console.info(data)excel.export_json_to_excel({header: tHeader,data,filename: 'errorList'})})},// 格式化JSONformatModelJson (filterVal, list) {return list.map(v => filterVal.map(j => {return v[j]}))},
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errorList是从后端传过来的
exportExcel () {getErrorListExcel().then(response => {this.errList = response.data})}
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使用created方法，在加载.vue时，就调用/getErrorListExcel接口，获取errorList的值。
created () {this.exportExcel()},
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调用后端接口的api
import axios from 'axios'
export function getErrorListExcel () {return axios.get('http://127.0.0.1:8082/login/getErrorListExcel', {}).then(response => response).catch(error => error)
}
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后端接口设置errorList中的值
@GetMapping("/getErrorListExcel")public List<ErrorItemBO> getErrorListExcel() {List<ErrorItemBO> list = new ArrayList<>();for (int i = 0; i < 10; i++) {ErrorItemBO errorItemBO = new ErrorItemBO();errorItemBO.setItem("item" + i);errorItemBO.setError("error" + i);list.add(errorItemBO);}return list;}
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总结
如果涉及到文件下载，尽量后端传一个list，然后都在前端合成相应的文件以到达减轻服务器负担的作用。
最后
最近找到一个VUE的文档，它将VUE的各个知识点进行了总结，整理成了《Vue 开发必须知道的36个技巧》。内容比较详实，对各个知识点的讲解也十分到位。
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