在主内存中没有内容的情况下生成大型pdf

Question

我正在使用 iText 生成非常大的 pdf 格式表格。生成这些表而不是将全部内容存储在内存中的最佳方法是什么？如果我只是将 for 循环中的以下大小增加到 100 万，我运行内存不足，有没有比将整个内容都放在内存中更好的流式传输方式

我看到了这个postHow to directly stream large content to PDF with minimal memory footprint? 但我想知道要使用什么 iText api。

示例代码：

import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Date;

import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Element;
import com.itextpdf.text.Font;
import com.itextpdf.text.Font.FontFamily;
import com.itextpdf.text.Phrase;
import com.itextpdf.text.pdf.PdfPCell;
import com.itextpdf.text.pdf.PdfPTable;
import com.itextpdf.text.pdf.PdfWriter;

public class SimpleTable11 {
public final static String DEST = "/Users/.../Documents/test23.pdf";

public static void main(String[] args) throws IOException, DocumentException {
    new SimpleTable11().createPdf(DEST);
}

public void createPdf(String dest) throws IOException, DocumentException {

    System.out.println(new Date());
    Document document = new Document();
    PdfWriter.getInstance(document, new FileOutputStream(DEST));
    document.open();
    PdfPTable table = new PdfPTable(23);
    table.setWidths(new int[] { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 });
    table.setWidthPercentage(100);
    table.addCell(createCell("Account", 2, 1, Element.ALIGN_JUSTIFIED));
    table.addCell(createCell("Org Id", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Contract Number", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Transaction Type", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Transaction Number", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Transaction Date", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Start Date", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("End Date", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Billing Reference", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Line Description", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Product Name", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Related Invoices", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Monthly Unit Price", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("quantity", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Total Line Tax", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Total Price", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Exchange Rate", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Taxable", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Vat Rate", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("VAT", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Taxable", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("VAT", 2, 1, Element.ALIGN_LEFT));
    table.addCell(createCell("Total Price", 2, 1, Element.ALIGN_LEFT));

    String[] data = { "44445555", "123456", "0105567", "INV", "123456", "10/10/2018", "11/15/2018", "11/20/2050",
            "SO-0000000000-Mento", "Marketing Product", "Marketing Product ", "Marketing Product",
            "Marketing Product", "0.00", "12.56", "300.00", "0.566667345", "12.54", "10.00%", "12.56", "7.58",
            "7.27", "176.67" };
    for (int i = 0; i < 20000; i++) {
        for (int j = 0; j < data.length; j++) {
            table.addCell(createCell(data[j], 1, 1, Element.ALIGN_LEFT));
        }
    }
    document.add(table);
    document.close();
    System.out.println(new Date());
}

public PdfPCell createCell(String content, float borderWidth, int colspan, int alignment) {
    Font font = new Font(FontFamily.HELVETICA, 4, Font.NORMAL);
    PdfPCell cell = new PdfPCell(new Phrase(content, font));
    cell.setBorderWidth(borderWidth);
    cell.setColspan(colspan);
    cell.setHorizontalAlignment(alignment);
    return cell;
}

}

Answer 1

当使用具有很多单元格的 PdfPTable 对象时，您应该使用 class 实现 LargeElement ，它被记录为

/**
 * Interface implemented by Element objects that can potentially consume
 * a lot of memory. Objects implementing the LargeElement interface can
 * be added to a Document more than once. If you have invoked setComplete(false),
 * they will be added partially and the content that was added will be
 * removed until you've invoked setComplete(true);
 * @since   iText 2.0.8
 */
public interface LargeElement extends Element

即你应该先使用

setComplete(false),

然后向 table 添加一些内容（例如 20 行），然后向文档添加 table，添加更多内容，再次向文档添加 table , 等等...，当全部添加时，使用

setComplete(true)

并再次添加 table。这样 table 数据就不会保留在堆上，而是一点一点地序列化并写入写入器。

顺便说一句，还有其他 iText classes 也实现了 LargeElement。如果您对 iText 的大量内存消耗有疑问，您应该始终检查添加到 Document 的对象：如果它们实现了 LargeElement，首先尝试将它们转发到 Document 片段如上所述逐件。

在主内存中没有内容的情况下生成大型pdf

Generating large pdf without having content in main memory

java

pdf

pdf-generation

itext