一、依赖

   <spire.pdf.free.version>9.13.0</spire.pdf.free.version><itextpdf.version>5.5.13</itextpdf.version><dependency><groupId>e-iceblue</groupId><artifactId>spire.pdf.free</artifactId><version>${spire.pdf.free.version}</version></dependency><dependency><groupId>com.itextpdf</groupId><artifactId>itextpdf</artifactId><version>${itextpdf.version}</version></dependency>

二、思路：

①问题：

1、spire.pdf.free只能免费转换每个PDF的前三页

2、转换速度慢

3、多线程合并后页数顺序问题

②解决

1、将PDF文档根据页数截断为多个PDF，每个PDF最多三页

2、使用线程池多线程异步处理

3、map里的索引

三、代码：

1、 转换的类

package com.shiqiao.nev.business.infra.adapter.pdftoPic;import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.PdfCopy;
import com.itextpdf.text.pdf.PdfImportedPage;
import com.itextpdf.text.pdf.PdfReader;
import com.spire.pdf.PdfDocument;
import com.spire.pdf.graphics.PdfImageType;import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;public class PdfToPicConverter {private final byte[] pdfFileByteStream;private final Integer pageCount;private List<InputStream> picResult;public PdfToPicConverter(InputStream pdfFile) {try {pdfFileByteStream = inputStreamToByteArray(pdfFile);} catch (Exception e) {throw new RuntimeException("pdf文件转换为字节流失败", e);}PdfDocument pdf = new PdfDocument();pdf.loadFromStream(new ByteArrayInputStream(pdfFileByteStream));pageCount = pdf.getPages().getCount();}public PdfToPicConverter(byte[] pdfFile) {pdfFileByteStream = pdfFile;PdfDocument pdf = new PdfDocument();pdf.loadFromStream(new ByteArrayInputStream(pdfFileByteStream));pageCount = pdf.getPages().getCount();}public List<InputStream> convertToPictures(ExecutorService executorService) {picResult = new ArrayList<>();// 每三页为一组int groupSize = 3;int numGroups = (pageCount + groupSize - 1) / groupSize;List<Future<List<InputStream>>> futures = new ArrayList<>();for (int i = 0; i < numGroups; i++) {int startPage = i * groupSize;int endPage = Math.min(startPage + groupSize, pageCount);if (executorService != null) {futures.add(executorService.submit(() -> convertGroup(startPage, endPage)));}}// 等待所有任务完成并合并结果for (Future<List<InputStream>> future : futures) {try {picResult.addAll(future.get());} catch (Exception e) {throw new RuntimeException("图片转换失败", e);}}return picResult;}private InputStream splitPDFFile(byte[] pdfFileByteStream, int from, int end) {Document document = null;PdfCopy copy = null;try (ByteArrayInputStream bais = new ByteArrayInputStream(pdfFileByteStream);ByteArrayOutputStream baos = new ByteArrayOutputStream()) {PdfReader reader = new PdfReader(bais);int n = reader.getNumberOfPages();if (end == 0 || end > n) {end = n;}document = new Document(reader.getPageSize(1));copy = new PdfCopy(document, baos);document.open();for (int j = from + 1; j <= end; j++) {  // 注意这里j从from+1开始document.newPage();PdfImportedPage page = copy.getImportedPage(reader, j);copy.addPage(page);}document.close();return new ByteArrayInputStream(baos.toByteArray());} catch (IOException | DocumentException e) {throw new RuntimeException("PDF文件拆分失败", e);}}private List<InputStream> convertGroup(int startPage, int endPage) {InputStream inputStream = splitPDFFile(pdfFileByteStream, startPage, endPage);PdfDocument pdf = new PdfDocument();pdf.loadFromStream(inputStream);int end = endPage - startPage;List<InputStream> groupResult = new ArrayList<>();for (int i = 0; i < end; i++) {BufferedImage image = pdf.saveAsImage(i, PdfImageType.Bitmap, 500, 500);try (ByteArrayOutputStream baos = new ByteArrayOutputStream()) {ImageIO.write(image, "PNG", baos);groupResult.add(new ByteArrayInputStream(baos.toByteArray()));} catch (IOException e) {throw new RuntimeException("图片保存失败", e);}}pdf.close();return groupResult;return new ArrayList<>();}protected byte[] inputStreamToByteArray(InputStream inputStream) throws IOException {int bufferSize = 4096;byte[] buffer = new byte[bufferSize];int bytesRead;ByteArrayOutputStream baos = new ByteArrayOutputStream();while ((bytesRead = inputStream.read(buffer)) != -1) {baos.write(buffer, 0, bytesRead);}return baos.toByteArray();}
}

2、使用的地方

  public List<FileDTO> pdfToPng(byte[] filebyte, String fileName) {List<FileDTO> fileDTOS = new ArrayList<>();PdfToPicConverter pdfToPicConverter = new PdfToPicConverter(filebyte);List<InputStream> inputStreams = pdfToPicConverter.convertToPictures(pdfCovertPicExectorPool);inputStreams.forEach((e) -> {// 生成文件名String pgnNames = "fileName"+inputStreams.indexOf(e) + ".png";FileDTO fileDTO = new FileDTO(e, pgnNames);fileDTOS.add(fileDTO);});return fileDTOS;}

四、spire.pdf.free 的下载：maven仓库里进去然后点官网就能下jar包了