Java Apache POI SXSSF 和 XSSF

Apache POI SXSSF and XSSF

提问by Stepan Pogosyan

I have one question. Am I right that if I have a workbook which is created through xssfconstructor then it is enough to change the constructor to sxssfworkbook (with xssfwb passed as an argument) to make it work in a stream mode? Thanks a lof for your answers.

我有一个问题。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（将xssfwb 作为参数传递）以使其在stream mode. 谢谢你的回答。

Solution: It all depends on the classes which you use for streaming. If your class gathers more stream buffers than it can hold, this thing won't work. Otherwise it will

解决方案：这完全取决于您用于流式传输的类。如果您的类收集的流缓冲区多于它可以容纳的数量，则此操作将不起作用。否则会

采纳答案by pepuch

Yes, you're right. The difference between these two implementations is that stream version writes data directly to stream and stores at most specified number of rows in memory (default value is 100 and it's stored in SXSSFWorkbook.DEFAULT_WINDOW_SIZE). Because of that you won't be able to get some row data after writing to output stream. Big benefit of using stream implementation is less memory usage. If you need to export a lot of data just use SXSSFWorkbook.

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存储最多指定数量的行（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。使用流实现的一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。

Example:

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;
        }

    }

}

Output:

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

As you see row 1 is not accessible any more after writing to output stream with SXSSFWorkbook.

如您所见，在使用 SXSSFWorkbook 写入输出流后，第 1 行不再可访问。