flux讀取不到資料_使用webflux提升資料導出效率

序

本文主要研究一下如何使用webflux提升資料導出效率

傳統導出

@GetMapping("/download-old")

public ResponseEntity 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);

}

這裡模拟的是等所有資料都準備好了再導出，這種速度肯定慢，差不多需要等待100秒浏覽器才能彈出下載下傳框，如果前面有網關，很容易在網關那裡逾時了

webflux導出

@GetMapping("/download")

public Mono downloadByWriteWith(ServerHttpResponse response) throws IOException {

response.getHeaders().set(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=demo.xls");

response.getHeaders().add("Accept-Ranges", "bytes");

Flux flux = excelService.export(1000);

return response.writeWith(flux);

}

public Flux 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();

});

}

這裡使用ReactiveHttpOutputMessage的writeWith(Publisher extends DataBuffer> body)方法，實作邊準備資料邊導出

等待十幾秒就彈下載下傳框，之後就server端一邊輸出，浏覽器一邊下載下傳，100秒左右下載下傳完畢

小結

兩種方法目前看來用時差不多，不過後者可以避免逾時。當然使用傳統mvc也可以實作類似效果，就是拿到response的輸出流不斷地write和flush。不過webflux可以配合reactive的repository，實作端到端的reactive stream，同時也可以避免OOM。