【java批量导出pdf】优化方案

问题情境：

项目中存在web页面点击一键导出，导出所有数据对应的pdf文件，由于有些pdf文件是实时生成的，之前最简答的写法for循环处理速度太慢，超过了nginx配置的最大响应时间了，且对用户交互体验上很不友好，所以进一步进行优化。

解决方案：

1.对大量的数据进行分段处理；（向上取余）
代码示例：

public List<List<FrApplyGuaranteeInfo>> segmentList(List<FrApplyGuaranteeInfo> list ,int segmentSize) {
        int limit = (list.size() + segmentSize - 1) / segmentSize;
        List<List<FrApplyGuaranteeInfo>> segmentList =
                Stream.iterate(0, n -> n + 1).limit(limit).parallel().map(a -> list.stream().
                        skip(a * segmentSize).limit(segmentSize).parallel().collect(Collectors.toList())).collect(Collectors.toList());
        return segmentList;
    }
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2.通过threadPoolTaskExcetor.submit()方法进行多线程任务处理
示例代码：
第一步分段处理后的list

lists.forEach({list->{
   threadPoolExecutor.submit(new xxxxTask());
})
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第二步：具体的task需要实现callalbe
示例代码如下：

@Slf4j
public class DownloadLetterZipTask implements Callable {
    
   // 需要预审的记录    
   private List<FrApplyGuaranteeInfo> dataList;
   private ZipOutputStream zipOutputStream;
   private CountDownLatch countDownLatch;
   private IFrApplyGuaranteeInfoService applyGuaranteeInfoService;
   public DownloadLetterZipTask(List<FrApplyGuaranteeInfo> dataList, ZipOutputStream zipOutputStream, CountDownLatch countDownLatch, IFrApplyGuaranteeInfoService applyGuaranteeInfoService)
   {    this.dataList = dataList;
       this.zipOutputStream = zipOutputStream;      
       this.countDownLatch = countDownLatch;      
       this.applyGuaranteeInfoService = applyGuaranteeInfoService;    }
    @Override
    public Object call() throws Exception {
       log.info("start--------------" + Thread.currentThread().getName());        
       try {           
           for (FrApplyGuaranteeInfo applyGuaranteeInfo : dataList) {
               if (!StringUtils.isEmpty(applyGuaranteeInfo.getAcceptNo())) {
                   try {
                       // 这一步为具体的将文件转为字节数组输出流
                       ByteArrayOutputStream waterOutputStream = applyGuaranteeInfoService.getLetterPdfByteStream(applyGuaranteeInfo.getAcceptNo());
                       byte[] xmpMetadata = waterOutputStream.toByteArray();
                       synchronized (zipOutputStream) {
                           zipOutputStream.putNextEntry(new ZipEntry(applyGuaranteeInfo.getGenerateeLetterNo() + ".pdf"));
                           zipOutputStream.write(xmpMetadata);
                           zipOutputStream.closeEntry();
                       }
                   } catch (Exception e) {
                       log.error("[一键导出]---acceptNo为{}生成pdf失败", applyGuaranteeInfo.getAcceptNo());
                   }
               }
           }
       } catch (Exception e) {
           e.printStackTrace();
           log.error("[xxxx]-批量下载zip失败");

       } finally {
           countDownLatch.countDown();
          }
       return null;
      }
   }
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