image not displaying in PDF template using Spring Boot, flying saucer and Thymeleaf

Question

I create a file pdf from html template using Spring Boot, flying saucer, thymeleaf. But image is not displaying in my file.

Project structure:

code html:

<div class="col-xs-6 invoice-col-2">
   <img src="../static/images/mastercard.png" alt="mastercard"></img>
</div>

When I change img tag to:

<img src="../static/images/mastercard.png" alt="mastercard" th:src="@{static/images/mastercard.png}"></img>

When I create PDF file, I get an error:

org.thymeleaf.exceptions.TemplateProcessingException: Link base "static/images/mastercard.png" cannot be context relative (/) or page relative unless you implement the org.thymeleaf.context.IWebContext interface (context is of class: org.thymeleaf.context.Context)

Answer 1

Try using Spring's classpath: prefix. This loads your file directly from the classpath, no matter if you are running from a .jar or within your IDE. Here is an example:

<img alt="mastercard" th:src="@{classpath:static/images/mastercard.png}" />

More information about classpath: can be found in the official documentation.

Answer 2

In order to embed an image in a PDF generated by Flying Saucer,

1) Convert the image to a base64 encoded string.

Path path = Paths.get("src/main/resources/static/images/mastercard.png");
String base64Image = convertToBase64(path);

Function to convert image stored in a path like shown above, to a base64 encoded string

private String convertToBase64(Path path) {
    byte[] imageAsBytes = new byte[0];
    try {
      Resource resource = new UrlResource(path.toUri());
      InputStream inputStream = resource.getInputStream();
      imageAsBytes = IOUtils.toByteArray(inputStream);

    } catch (IOException e) {
      System.out.println("\n File read Exception");
    }

    return Base64.getEncoder().encodeToString(imageAsBytes);
  }

2) Set the base64 encoded image in the thymeleaf context

    Context context = new Context();
    String image = "data:image/png;base64, " + base64Image;
    context.setVariable("image",  image);

    String html = templateEngine.process("template", context);

3) In HTML, set the value of image as shown below:

<img th:src="${image}" style="width: 200px; height=100px"/>

4) Finally, render the HTML template to PDF

  ITextRenderer renderer = new ITextRenderer();
  renderer.setDocumentFromString(html); // html -> String created in Step 2
  renderer.layout();
  final ByteArrayOutputStream baos = new ByteArrayOutputStream();
  renderer.createPDF(baos)

Now you have the byteArrayOutputStream of the generated PDF, with which you can choose to store them to a file server or serve it to a client in a format of your choice.