生成大型pdf，而主存储器中没有内容 [英] Generating large pdf without having content in main memory

问题描述

我正在使用iText生成pdf格式的非常大的表. 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一百万，我用完了内存，是否有比将全部内容都存储在内存中更好的流传输方法

I am using iText to generate very large tables in pdf format. What is the best way to generate these tables instead of having the entire content in memory? If I just increase the below size in the for loop to a million I run out of memory, is there a better way to stream it than having the entire content in memory

我看到了此帖子如何可以以最少的内存占用量直接将大量内容流式传输到PDF? 但是我想知道要使用什么iText api.

I saw this post How to directly stream large content to PDF with minimal memory footprint? But I want to know what iText api to use.

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;
}

}

推荐答案

在单元格中使用PdfPTable对象时，应使用实现LargeElement的类，该类记录为

When using PdfPTable objects with very many cells you should make use of that class implementing LargeElement which is documented as

/**
 * 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

即您应该先使用

setComplete(false),

然后将一些内容(例如20行)添加到表中，然后将表添加到文档中，添加更多内容，再次将表添加到文档中，依此类推，等等.添加所有内容后，使用

then add some content (e.g. 20 rows) to the table, then add the table to the document, add some more content, add the table to the document again, etc..., and when all is added, use

setComplete(true)

，然后再次添加表格.这样，表数据就不会保留在堆中，而是一点一点地序列化并写入写程序.

and add the table once more. That way the table data does not remain on the heap but gets bit by bit serialized and written to the writer.

顺便说一句，还有其他实现LargeElement的iText类.如果iText占用大量内存，则应始终检查添加到Document的对象:如果它们实现了LargeElement，请首先尝试将它们逐段转发到Document.

As an aside, there are other iText classes, too, which implement LargeElement. If you have issues with a huge memory consumption with iText, you should always check the objects you add to your Document: If they implement LargeElement, first try to forward them to the Document piece by piece as explained above.

这篇关于生成大型pdf，而主存储器中没有内容的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！