本文章向大家介绍将PDF页面大小转为A4格式---itextPdf实现，主要包括将PDF页面大小转为A4格式---itextPdf实现使用实例、应用技巧、基本知识点总结和需要注意事项，具有一定的参考价值，需要的朋友可以参考一下。

将PDF页面大小转为A4格式（itextPdf实现）

1. 引入相关jar包

<!-- https://mvnrepository.com/artifact/com.itextpdf/itextpdf --><dependency><groupId>com.itextpdf</groupId><artifactId>itextpdf</artifactId><version>5.5.13.2</version></dependency>

2. 实现代码

package com.fan.study.common.util;import com.itextpdf.text.Document;
import com.itextpdf.text.PageSize;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfImportedPage;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfWriter;import java.awt.geom.AffineTransform;
import java.io.FileOutputStream;public class PdfConvertA4Utils {/*** @Param source 源文件* @Param target 转换后文件* @Description 将PDF转为A4格式* @Date: 2021/4/25**/private static void convert(String source, String target) {try {PdfReader pdfReader = new PdfReader(source);Document doc = new Document();PdfWriter writer = PdfWriter.getInstance(doc, new FileOutputStream(target));doc.open();PdfContentByte cb = writer.getDirectContent();for(int i = 1; i <= pdfReader.getNumberOfPages(); i++){PdfImportedPage page = writer.getImportedPage(pdfReader, i);float width = page.getWidth();float height = page.getHeight();if(height > width) {//横向doc.setPageSize(PageSize.A4);doc.newPage();//计算比例float widthScale = getWidthScale(width);float heightScale = getHeightScale(height);//addTemplate方法中有6个float类型的参数，是通过二维图像仿射变换得到的//cb.addTemplate(page, new AffineTransform(widthScale, 0, 0, heightScale,0,0));//二维图像仿射变换:https://www.cnblogs.com/v2m_/archive/2013/05/09/3070187.htmlcb.addTemplate(page, widthScale, 0, 0, heightScale,0,0);} else {//纵向doc.setPageSize(new com.itextpdf.text.Rectangle(PageSize.A4.getHeight(), PageSize.A4.getWidth()));doc.newPage();float widthScale = getWidthScale(height);float heightScale = getHeightScale(width);cb.addTemplate(page, widthScale, 0, 0, heightScale,0,0);}}doc.close();} catch (Exception ex) {ex.printStackTrace();}}private static float getWidthScale(float width) {float scale = PageSize.A4.getWidth() / width;return scale;}private static float getHeightScale(float height) {float scale = PageSize.A4.getHeight() / height;return scale;}
}