Apache POI XSSFWorkbook内存泄漏

Question

所以我正在用Java制作一个大规模的素数生成器（在JavaFX的帮助下）。

它使用Apache POI库（我相信我使用的是V3.17)将结果输出到Excel电子表格。

此导出逻辑的静态方法保存在一个名为ExcelWriter的类中。基本上，它遍历Arraylist参数，并用它的内容填充XSSFWorkbook。FileOutputStream实际上是用来使它成为一个excel文件的。下面是它的相关部分：

public class ExcelWriter {

//Configured JFileChooser to make alert before overwriting old files
private static JFileChooser fileManager = new JFileChooser(){
@Override
public void approveSelection(){
    ...
}        
};


private static FileFilter filter = new FileNameExtensionFilter("Excel files","xlsx");
private static boolean hasBeenInitialized = false;



//Only method that can be called externally to access this class's functionality
public static <T extends Object> void makeSpreadsheet
    (ArrayList<T> list,  spreadsheetTypes type, int max, String title, JFXProgressBar progressBar) 
            throws IOException, InterruptedException{
    progressBar.progressProperty().setValue(0);
    switch (type){
        case rightToLeftColumnLimit:
            makeSpreadsheetRightToLeft(list, false, max, title, progressBar);
            break;
       ...
    }
}


static private <T extends Object> void makeSpreadsheetRightToLeft
    (ArrayList<T> list,  boolean maxRows, int max, String title, JFXProgressBar progressBar) 
            throws IOException, InterruptedException{
    initializeChooser();
    XSSFWorkbook workbook = new XSSFWorkbook();
    XSSFSheet sheet = workbook.createSheet("Primus output"); 
    int rowPointer = 0;
    int columnPointer = 0;
    double progressIncrementValue = 1/(double)list.size();

    //Giving the spreadsheet an internal title also
    Row row = sheet.createRow(0);
    row.createCell(0).setCellValue(title);

    row = sheet.createRow(++rowPointer);

    //Making the sheet with a max column limit
    if (!maxRows){            
        for (T number: list){ 
            if (columnPointer == max){
                columnPointer = 0;
                row = sheet.createRow(++rowPointer);
            }
            Cell cell = row.createCell(columnPointer++);
            progressBar.setProgress(progressBar.getProgress() + progressIncrementValue);
            cell.setCellValue(number.toString());             
        }
    }else {
        //Making the sheet with a max row limit
        int columnWrapIndex = (int)Math.ceil(list.size()/(float)max);
        for (T number: list){ 
            if (columnPointer == columnWrapIndex){
                columnPointer = 0;
                row = sheet.createRow(++rowPointer);
            }
            Cell cell = row.createCell(columnPointer++);
            progressBar.setProgress(progressBar.getProgress() + progressIncrementValue);
            cell.setCellValue(number.toString());
        }         
    }
    writeToExcel(workbook, progressBar);


}


static private void writeToExcel(XSSFWorkbook book, JFXProgressBar progressBar) throws IOException, InterruptedException{
    //Exporting to Excel
    int returnValue = fileManager.showSaveDialog(null);

    if (returnValue == JFileChooser.APPROVE_OPTION){
        File file = fileManager.getSelectedFile();

        //Validation logic here


        try{

            FileOutputStream out = new FileOutputStream(file);
            book.write(out);
            out.close();
            book.close();
        }catch (FileNotFoundException ex){

        } 

    }
}
}

之后,我的FXML文档控制器有一个buttonListerner,它调用：

longCalculationThread thread = new longCalculationThread(threadBundle);
thread.start();

longcalculationthread创建了一个大约有100万个素数的列表，并使用以下代码将它们导出到ExcelWriter：

private void publishResults() throws IOException, InterruptedException{
    if (!longResults.isEmpty()){
        if (shouldExport) {
            progressText.setText("Exporting to Excel...");
            ExcelWriter.makeSpreadsheet(longResults, exportType, excelExportLimit, getTitle(), progressBar);

    }
   }

问题是，即使在XSSF工作簿中保存工作簿的变量是它所使用的方法的局部变量，但之后它不会被垃圾回收。

它占用了大约1.5GB的RAM（我不知道为什么），并且只有在调用另一个巨大的导出时才会重新分配这些数据（不是用于小的导出）。我的问题并不是真的需要大量的RAM，而是即使方法完成了，内存也没有GCED。下面是我的NetBeans个人资料的一些图片：

Answer 1

我找到答案了！我必须用system.GC（）提示GC。我记得早些时候试过这个，但是我一定是在工作簿仍然可以访问的情况下进行的，因此无法进行GCED。