思路:base64 -> multipartFile - > pdf

base64 -> multipartFile

/**
 *   将 图片base64 - > MultipartFile
 * @param base64
 * @return
 */
public static MultipartFile base64MultipartFile(String base64) {
    
    try {
    
        String[] baseStr = base64.split(",");
        BASE64Decoder base64Decoder = new BASE64Decoder();
        byte[] b;
        b = base64Decoder.decodeBuffer(baseStr[1]);
        for (int i = 0; i < b.length; ++i) {
    
            if (b[i] < 0) {
    
                b[i] += 256;
            }
        }
        return new BASE64DecodedMultipartFile(b, baseStr[0]);
    } catch (Exception e) {
    
        e.printStackTrace();
        return null;
    }
}

multipartFile - > pdf

/**
 * 将图片转换为PDF文件
 *
 * @param file SpringMVC获取的图片文件
 * @return PDF文件
 * @throws IOException       IO异常
 * @throws DocumentException PDF文档异常
 */
private static File generatePdfFile(MultipartFile file) throws IOException, DocumentException {
    
    String fileName = file.getOriginalFilename();
    String pdfFileName;
    if (fileName != null) {
    
        pdfFileName = fileName.substring(0, fileName.lastIndexOf(".")) + ".pdf";
    } else {
    
        return null;
    }
    Document doc = new Document(PageSize.A4, 100, 100, 20, 30);
    PdfWriter.getInstance(doc, new FileOutputStream(pdfFileName));
    doc.open();
    doc.newPage();
    Image image = Image.getInstance(file.getBytes());
    float height = image.getHeight();
    float width = image.getWidth();
    int percent = getPercent(height, width);
    image.setAlignment(Image.MIDDLE);
    image.scalePercent(percent);
    doc.add(image);
    doc.close();
    return new File(pdfFileName);
}



	/**
	 * 等比压缩，获取压缩百分比
	 * @param height 图片的高度
	 * @param weight 图片的宽度
	 * @return 压缩百分比
	 */
	private static int getPercent(float height, float weight) {
    
		float percent;
		if (height > weight) {
    
			percent = PageSize.A4.getHeight() / height * 100;
		} else {
    
			percent = PageSize.A4.getWidth() / weight * 100;
		}
		// -5 多缩放一点 不影响内容
		percent -= 5;
		return Math.round(percent);
	}

如果还需要转成multipartFile方便调用api上传的话

pdf file - > multipartFile

FileInputStream input = new FileInputStream(file);

MultipartFile multipartFilePDF = new MockMultipartFile("file", file.getName(), "text/plain", IOUtils.toByteArray(input));

pom 依赖 itextpdf

   <dependency>
        <groupId>com.itextpdf</groupId>
        <artifactId>itextpdf</artifactId>
        <version>5.5.10</version>
    </dependency>