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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 row
            sink.next(stringBuffer(ExcelUtil.writeTitleRow(Sets.newHashSet("title","content"))));
            //write data row
            IntStream.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。