[case6]使用webflux提高數據導出效率

序

本文主要研究一下如何使用webflux提高數據導出效率

傳統導出

@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);
    }

這裏模擬的是等全部數據都準備好了再導出，這種速度確定慢，差很少須要等待100秒瀏覽器才能彈出下載框，若是前面有網關，很容易在網關那裏超時了

webflux導出

@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();
        });
    }

這裏使用ReactiveHttpOutputMessage的writeWith(Publisher<? extends DataBuffer> body)方法，實現邊準備數據邊導出
等待十幾秒就彈下載框，以後就server端一邊輸出，瀏覽器一邊下載，100秒左右下載完畢

小結

兩種方法目前看來用時差很少，不事後者能夠避免超時。固然使用傳統mvc也能夠實現相似效果，就是拿到response的輸出流不斷地write和flush。不過webflux能夠配合reactive的repository，實現端到端的reactive stream，同時也能夠避免OOM。