Apache POI SXSSF和XSSF

Question

我有一個問題。 我是對的，如果我有一個通過xssf構造函數創建的工作簿，那么將構造函數更改為sxssf工作簿（將xssf wb作為參數傳遞）就足以使其在stream mode工作了嗎？ 謝謝你的答案。

解決方案：這完全取決於您用於流式傳輸的類。 如果你的類收集的流緩沖區比它能容納的多，那么這個東西就不行了。 否則它會

Answer 1

你是對的。 這兩個實現之間的區別在於流版本將數據直接寫入流並在內存中存儲最多指定行數（默認值為100，並且存儲在SXSSFWorkbook.DEFAULT_WINDOW_SIZE中）。 因此，在寫入輸出流之后，您將無法獲得某些行數據。 使用流實現的巨大好處是減少內存使用。 如果您需要導出大量數據，請使用SXSSFWorkbook。

例：

public static void main(String[] args) throws IOException {
        FileOutputStream inMemoryOut = new FileOutputStream(new File("inMemoryWorkbook.xlsx"));
        XSSFWorkbook workbook = new XSSFWorkbook();
        WorkbookExample example = new WorkbookExample(workbook, inMemoryOut);
        example.export();

        FileOutputStream streamOut = new FileOutputStream(new File("streamWorkbook.xlsx"));
        SXSSFWorkbook streamWorkbook = new SXSSFWorkbook();
        WorkbookExample streamExample = new WorkbookExample(streamWorkbook, streamOut);
        streamExample.export();
    }

public class WorkbookExample {

    private Logger logger = Logger.getLogger(WorkbookExample.class.getName());
    private Workbook workbook;
    private OutputStream out;

    public WorkbookExample(Workbook workbook, OutputStream out) {
        this.workbook = workbook;
        this.out = out;
    }

    public void export() throws IOException {
        logger.info("export start for " + workbook.getClass().getName());

        List<Person> persons = new ArrayList<Person>();
        for (int i = 0; i < 1000; i++) {
            persons.add(new Person(String.valueOf("user_" + i)));
        }

        Sheet sheet = workbook.createSheet();
        for (int i = 0; i < persons.size(); i++) {
            Person p = persons.get(i);
            Row row = sheet.createRow(i);
            Cell cell = row.createCell(0);
            cell.setCellValue(p.getName());
        }
        workbook.write(out);
        logger.info("Is row 1 accessible after writing to output stream? " + String.valueOf(sheet.getRow(1) != null));
        out.close();
        workbook.close();

        logger.info("export finished for " + workbook.getClass().getName());
    }

    public static class Person {

        private String name;

        public Person(String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

    }

}

輸出：

kwi 21, 2015 7:56:14 PM pepuch.html2pdf.WorkbookExample export
    INFO: export start for org.apache.poi.xssf.usermodel.XSSFWorkbook
kwi 21, 2015 7:56:15 PM pepuch.html2pdf.WorkbookExample export
    INFO: Is row 1 accessible after writing to output stream? true
kwi 21, 2015 7:56:15 PM pepuch.html2pdf.WorkbookExample export
    INFO: export finished for org.apache.poi.xssf.usermodel.XSSFWorkbook
kwi 21, 2015 7:56:15 PM pepuch.html2pdf.WorkbookExample export
    INFO: export start for org.apache.poi.xssf.streaming.SXSSFWorkbook
kwi 21, 2015 7:56:15 PM pepuch.html2pdf.WorkbookExample export
    INFO: Is row 1 accessible after writing to output stream? false
kwi 21, 2015 7:56:15 PM pepuch.html2pdf.WorkbookExample export
    INFO: export finished for org.apache.poi.xssf.streaming.SXSSFWorkbook

如您所見，在使用SXSSFWorkbook寫入輸出流后，無法再訪問第1行。