java - Apache POI SXSSF 和 XSSF

Question

我有一个问题。我是对的，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 工作簿就足够了(使用 xssf wb 作为参数传递)以使其在 流模式 下工作？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。如果您的类(class)收集的流缓冲区多于它可以容纳的数量，那么这个东西将无法工作。否则会

Answer 1

是的，你是对的。这两种实现方式的区别在于，stream 版本直接将数据写入stream 并在内存中存储最多指定行数(默认值为100，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。

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，第 1 行不再可访问。