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本文主要研究一下如何使用webflux提升数据导出效率

传统导出

    @GetMapping("/download-old")public ResponseEntity<Resource> downloadInOldWays(){return ResponseEntity.ok().header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=demo.xls").header("Accept-Ranges", "bytes").body(new ByteArrayResource(exportBytes(1000)));}public byte[] exportBytes(int dataRow){StringBuilder output = new StringBuilder();output.append(ExcelUtil.startWorkbook());output.append(ExcelUtil.startSheet());output.append(ExcelUtil.startTable());output.append(ExcelUtil.writeTitleRow(Sets.newHashSet("title","content")));IntStream.rangeClosed(1,dataRow).forEach(i -> {try {TimeUnit.MILLISECONDS.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}output.append(ExcelUtil.writeDataRow(Lists.newArrayList("title"+i,"content"+i)));});output.append(ExcelUtil.endTable());output.append(ExcelUtil.endSheet());output.append(ExcelUtil.endWorkbook());return output.toString().getBytes(StandardCharsets.UTF_8);}

这里模拟的是等所有数据都准备好了再导出，这种速度肯定慢，差不多需要等待100秒浏览器才能弹出下载框，如果前面有网关，很容易在网关那里超时了

webflux导出

    @GetMapping("/download")public Mono<Void> downloadByWriteWith(ServerHttpResponse response) throws IOException {response.getHeaders().set(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=demo.xls");response.getHeaders().add("Accept-Ranges", "bytes");Flux<DataBuffer> flux = excelService.export(1000);return response.writeWith(flux);}public Flux<DataBuffer> export(int dataRow){return Flux.create(sink -> {sink.next(stringBuffer(ExcelUtil.startWorkbook()));sink.next(stringBuffer(ExcelUtil.startSheet()));sink.next(stringBuffer(ExcelUtil.startTable()));//write title rowsink.next(stringBuffer(ExcelUtil.writeTitleRow(Sets.newHashSet("title","content"))));//write data rowIntStream.rangeClosed(1,dataRow).forEach(i -> {try {TimeUnit.MILLISECONDS.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}sink.next(stringBuffer(ExcelUtil.writeDataRow(Lists.newArrayList("title"+i,"content"+i))));});sink.next(stringBuffer(ExcelUtil.endTable()));sink.next(stringBuffer(ExcelUtil.endSheet()));sink.next(stringBuffer(ExcelUtil.endWorkbook()));sink.complete();});}

这里使用ReactiveHttpOutputMessage的writeWith(Publisher<? extends DataBuffer> body)方法，实现边准备数据边导出 等待十几秒就弹下载框，之后就server端一边输出，浏览器一边下载，100秒左右下载完毕

小结

两种方法目前看来用时差不多，不过后者可以避免超时。当然使用传统mvc也可以实现类似效果，就是拿到response的输出流不断地write和flush。不过webflux可以配合reactive的repository，实现端到端的reactive stream，同时也可以避免OOM。