Apache POI SXSSF 和 XSSF

Question

我有一个问题。我是否正确，如果我有一个通过xssf 构造函数创建的工作簿，那么将构造函数更改为sxssf 工作簿（xssf wb 作为参数传递）以使其在stream mode 中工作就足够了?非常感谢您的回答。

解决方案：这完全取决于您用于流式传输的类。如果你的类收集的流缓冲区比它可以容纳的多，这件事就行不通了。否则会

Answer 1

是的，你是对的。这两种实现之间的区别在于流版本直接将数据写入流并在内存中最多存储指定数量的行（默认值为 100，它存储在 SXSSFWorkbook.DEFAULT_WINDOW_SIZE 中）。因此，在写入输出流后，您将无法获得一些行数据。使用流实现的最大好处是更少的内存使用。如果您需要导出大量数据，只需使用 SXSSFWorkbook。

例子：

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;
        }

    }

}

输出：

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

如您所见，在使用 SXSSFWorkbook 写入输出流后，无法再访问第 1 行。