springboot 使用免费的iText 包 实现pdf转图片

您好！使用iText进行PDF转图片需要用到iText的核心模块 `itextpdf` 和 `pdf-renderer` 模块。这两个模块都是免费的。以下是一个基于Spring Boot的示例，演示如何使用iText将PDF转换为图像：

首先，在您的pom.xml文件中添加以下依赖：

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13.2</version>
</dependency>
<dependency>
    <groupId>org.xhtmlrenderer</groupId>
    <artifactId>flying-saucer-pdf</artifactId>
    <version>9.1.22</version>
</dependency>

接下来，创建一个名为 `PdfToImageService` 的服务类，该类具有一个名为 `pdfToImage` 的方法，该方法将接受一个PDF文件路径作为输入，并返回一个图像列表：

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.PdfReader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;
import org.xhtmlrenderer.swing.Java2DRenderer;

import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

@Service
public class PdfToImageService {

    private static final Logger LOGGER = LoggerFactory.getLogger(PdfToImageService.class);

    public List<byte[]> pdfToImage(String pdfFilePath) throws IOException, DocumentException {
        LOGGER.info("Converting PDF to image: {}", pdfFilePath);

        List<byte[]> imageBytesList = new ArrayList<>();

        PdfReader pdfReader = new PdfReader(pdfFilePath);

        for (int page = 1; page <= pdfReader.getNumberOfPages(); page++) {
            LOGGER.info("Converting page {} of PDF: {}", page, pdfFilePath);

            // 使用Flying Saucer将PDF页面转换为BufferedImage
            Java2DRenderer renderer = new Java2DRenderer(pdfReader.getPageContent(page));
            BufferedImage bufferedImage = renderer.getImage();

            // 将BufferedImage转换为byte数组
            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
            javax.imageio.ImageIO.write(bufferedImage, "png", outputStream);
            imageBytesList.add(outputStream.toByteArray());

            outputStream.close();
        }

        pdfReader.close();

        return imageBytesList;
    }
}

最后，在您的控制器中注入 `PdfToImageService`，并将其用于将PDF转换为图像：

import com.itextpdf.text.DocumentException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.ByteArrayResource;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;

import java.io.IOException;
import java.util.List;

@Controller
@RequestMapping("/pdf-to-image")
public class PdfToImageController {

    private static final Logger LOGGER = LoggerFactory.getLogger(PdfToImageController.class);

    @Autowired
    private PdfToImageService pdfToImageService;

    @GetMapping(value = "/{pdfFileName}", produces = MediaType.IMAGE_PNG_VALUE)
    public ResponseEntity<ByteArrayResource> pdfToImage(@PathVariable String pdfFileName) throws IOException, DocumentException {
        LOGGER.info("Converting PDF to image: {}", pdfFileName);

        String pdfFilePath = "path/to/pdf/" + pdfFileName + ".pdf";

        List<byte[]> imageBytesList = pdfToImageService.pdfToImage(pdfFilePath);

        if (imageBytesList.isEmpty()) {
            return ResponseEntity.notFound().build();
        } else if (imageBytesList.size() == 1) {
            return ResponseEntity.ok(new ByteArrayResource(imageBytesList.get(0)));
        } else {
            // 将多个图像合并为一个图像
            // ...

            byte[] mergedImageBytes = new byte[0]; // 合并后的图像的字节数组
            return ResponseEntity.ok(new ByteArrayResource(mergedImageBytes));
        }
    }
}

这个示例代码假设您已经将要转换的PDF文件放在 `path/to/pdf` 目录下。当您访问 `/pdf-to-image/{pdfFileName}` 时，它将返回转换后的PNG图像。如果PDF文件具有多个页面，则可以将它们合并为一个图像，或者返回多个图像。希望这可以帮助到您！