java - 为什么我的程序越来越慢？

Question

我正在使用该程序将数据从数据库发送到 Excel 文件。它在开始时运行良好，然后变得越来越慢，最后它耗尽内存并出现以下错误:“java.lang.OutOfMemoryError:Java heap space ...”。

通过添加jvm heap sapce可以解决问题，但问题是运行程序耗时太长。

几分钟后，它完成了一个循环，用了 4 秒，可以在开始时用 0.5 秒完成。我找不到使它始终以特定速度运行的解决方案。

是我的代码问题吗？

有什么线索吗？

代码如下:

public void addAnswerRow(List<FinalUsers> finalUsersList,WritableWorkbook book){

   if (finalUsersList.size() >0 ) {
    try {
       WritableSheet  sheet = book.createSheet("Answer", 0);
       int colCount = 0;
       sheet.addCell(new Label(colCount++,0,"Number"));
       sheet.addCell(new Label(colCount++,0,"SchoolNumber"));
       sheet.addCell(new Label(colCount++,0,"District"));
       sheet.addCell(new Label(colCount++,0,"SchoolName"));
       sheet.setColumnView(1, 15);
       sheet.setColumnView(3, 25);

       List<Elements> elementsList = this.elementsManager.getObjectElementsByEduTypeAndQuestionnaireType(finalUsersList.get(0).getEducationType().getId(),     this.getQuestionnaireByFinalUsersType(finalUsersList.get(0).getFinalUsersType().getId()));

       Collections.sort(elementsList, new Comparator<Elements>(){

           public int compare(Elements o1, Elements o2) {

             for(int i=0; i< ( o1.getItemNO().length()>o2.getItemNO().length()?  o2.getItemNO().length(): o1.getItemNO().length());i++){
                  if (CommonFun.isNumberic(o1.getItemNO().substring(0, o1.getItemNO().length()>3? 4: o1.getItemNO().length()-1)) && !CommonFun.isNumberic(o2.getItemNO().substring(0, o2.getItemNO().length()>3? 4: o2.getItemNO().length()-1))){
                 return 1;
                  }
                 if (!CommonFun.isNumberic(o1.getItemNO().substring(0, o1.getItemNO().length()>3? 4: o1.getItemNO().length()-1)) && CommonFun.isNumberic(o2.getItemNO().substring(0,o2.getItemNO().length()>3? 4:o2.getItemNO().length()-1))){ 
                 return -1;
                 }  
                if ( o1.getItemNO().charAt(i)!=o2.getItemNO().charAt(i) ){

                    return   o1.getItemNO().charAt(i)-o2.getItemNO().charAt(i);
                 }
           }
           return  o1.getItemNO().length()> o2.getItemNO().length()? 1:-1;
       }});

       for (Elements elements : elementsList){
           sheet.addCell(new Label(colCount++,0,this.getTitlePre(finalUsersList.get(0).getFinalUsersType().getId(), finalUsersList.get(0).getEducationType().getId())+elements.getItemNO()+elements.getItem().getStem())); 
       }

       int sheetRowCount =1;
       int sheetColCount =0;

       for(FinalUsers finalUsers : finalUsersList){

          sheetColCount =0;

          sheet.addCell(new Label(sheetColCount++,sheetRowCount,String.valueOf(sheetRowCount)));
          sheet.addCell(new Label(sheetColCount++,sheetRowCount,finalUsers.getSchool().getSchoolNumber()));
          sheet.addCell(new Label(sheetColCount++,sheetRowCount,finalUsers.getSchool().getDistrict().getDistrictNumber().toString().trim()));
          sheet.addCell(new Label(sheetColCount++,sheetRowCount,finalUsers.getSchool().getName()));

          List<AnswerLog> answerLogList = this.answerLogManager.getAnswerLogByFinalUsers(finalUsers.getId());


          Map<String,String> answerMap = new HashMap<String,String>();

          for(AnswerLog answerLog :answerLogList ){
             if (answerLog.getOptionsId() != null)
             {
                answerMap.put(answerLog.getElement().getItemNO(), this.getOptionsAnswer(answerLog.getOptionsId()));
             }else if (answerLog.getBlanks()!= null){

                answerMap.put(answerLog.getElement().getItemNO(), answerLog.getBlanks());
             }else{

                answerMap.put(answerLog.getElement().getItemNO(), answerLog.getSubjectiveItemContent());  
             }   
          }
          for (Elements elements : elementsList){

             sheet.addCell(new Label(sheetColCount++,sheetRowCount,null==answerMap.get(elements.getItemNO())?"0":answerMap.get(elements.getItemNO())));

          }

         sheetRowCount++; 
       }

       book.write();
       book.close();

     } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
     } catch (RowsExceededException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     } catch (WriteException e) {

      // TODO Auto-generated catch block
      e.printStackTrace();
   }

}

Answer 1

您在某处创建对象并保留对它们的可达引用。

您可能正在将对象添加到集合中并且从未删除它们……所以集合只会增长直到内存耗尽。当您接近最大堆大小时，垃圾收集器会过度负担以寻找可用内存来重新组织事物，并且您越接近限制，程序就会呈指数级变慢。

此外，您可能每次都忘记关闭某些对象，例如您的工作簿。