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Yes. With iText pdfHTML, put the CSS text inside a <style> element in the HTML string, then call HtmlConverter.convertToPdf. Use the overload that accepts ConverterProperties and set a base URI whenever the HTML refers to relative stylesheets, images, or fonts.
The shortest working solution
For a self-contained document, no temporary CSS file is required. Build one HTML string, insert the stylesheet in the document head, and write the PDF to an output stream:
String css = "body { font-family: sans-serif; color: #222; }"
+ ".invoice { width: 100%; }";
String html = "<html><head><style>" + css + "</style></head>"
+ "<body><div class='invoice'>Invoice</div></body></html>";
try (OutputStream out = Files.newOutputStream(Path.of("out.pdf"))) {
HtmlConverter.convertToPdf(html, out);
}The convertToPdf(String, OutputStream) overload is intended for exactly this case: it converts a Java String containing HTML into PDF bytes in the supplied stream.
Prepare the Java project
Add iText’s com.itextpdf:html2pdf Maven artifact (the official iText installation documentation lists the current dependency coordinates), then import the converter classes and standard Java I/O types:
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import com.itextpdf.html2pdf.HtmlConverter;
import com.itextpdf.html2pdf.ConverterProperties;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Path;Choose the library version approved for your application rather than copying an unpinned version from an old example. Review iText’s licensing terms before release: AGPL licensing applies to non-commercial use, while commercial use requires a commercial license. Your deployment model, not just the fact that the code is internal, determines which terms apply.
Insert dynamic CSS into the HTML string
When CSS is generated at runtime, keep the HTML structure explicit and place the stylesheet in <head>. A StringBuilder is convenient when several rules or optional blocks are assembled:
StringBuilder html = new StringBuilder();
html.append("<!doctype html>")
.append("<html><head><meta charset='UTF-8'>")
.append("<style>")
.append("body { margin: 0; font-family: sans-serif; }")
.append(".total { font-weight: 700; text-align: right; }")
.append("</style></head>")
.append("<body><p class='total'>€123.45</p></body></html>");
try (OutputStream out = Files.newOutputStream(Path.of("invoice.pdf"))) {
HtmlConverter.convertToPdf(html.toString(), out);
}Keep CSS and markup separate in your application code until the final assembly. That makes escaping, testing, and template review easier. The resulting value still reaches pdfHTML as one HTML string; no CSS file has to be created.
Use a base URI for relative assets
Inline CSS solves the stylesheet problem, but it does not tell the renderer where a relative image, font, or linked resource lives. For markup such as <img src='images/logo.png'> or a font URL relative to the template directory, configure ConverterProperties.setBaseUri:
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ConverterProperties properties = new ConverterProperties()
.setBaseUri(Path.of("/srv/app/templates").toUri().toString());
String html = "<html><head>"
+ "<style>body { font-family: 'InvoiceFont'; }</style>"
+ "</head><body>"
+ "<img src='images/logo.png' alt='Company logo'>"
+ "</body></html>";
try (OutputStream out = Files.newOutputStream(Path.of("out.pdf"))) {
HtmlConverter.convertToPdf(html, out, properties);
}The base URI is the directory against which relative references are resolved. A relative URL cannot be interpreted reliably when the converter receives only an in-memory string, because the string has no filesystem location of its own. Set the URI to the directory that actually contains the referenced files, and verify that the Java process has permission to read them.
When to inline and when to reference
- Inline small, generated rules in
<style>when the document is self-contained. - Use a base URI for shared images, font files, or other assets maintained beside a template.
- Use stable, resolvable URLs for every resource; a browser resolving an asset on your workstation does not prove the server-side converter can resolve it.
Complete example with an external image and output file
This example combines generated CSS, a relative image, a base URI, and a try-with-resources output stream:
import com.itextpdf.html2pdf.ConverterProperties;
import com.itextpdf.html2pdf.HtmlConverter;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Path;
public class InvoicePdf {
public static void main(String[] args) throws Exception {
String css = "body { font-family: sans-serif; color: #222; }"
+ ".invoice { width: 100%; padding: 24px; }"
+ ".total { text-align: right; font-weight: bold; }";
String html = "<!doctype html><html><head>"
+ "<meta charset='UTF-8'><style>" + css + "</style>"
+ "</head><body>"
+ "<section class='invoice'>"
+ "<img src='images/logo.png' alt='Company logo'>"
+ "<h1>Invoice 1042</h1>"
+ "<p class='total'>$250.00</p>"
+ "</section></body></html>";
ConverterProperties properties = new ConverterProperties()
.setBaseUri(Path.of("/srv/app/templates").toUri().toString());
try (OutputStream out = Files.newOutputStream(Path.of("invoice-1042.pdf"))) {
HtmlConverter.convertToPdf(html, out, properties);
}
}
}The output file is complete when the method returns and the stream closes. For an HTTP endpoint, replace the file stream with the response’s output stream and set the response content type to application/pdf.
Understand pdfHTML’s CSS boundary
iText pdfHTML is an HTML/CSS renderer, not a full browser. Its feature matrix documents support for many common tags and paged-media rules, while identifying browser-oriented areas that are unsupported or partial, including scripts, CSS animations and transitions, CSS custom properties, and several modern layout features.
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Design templates for predictable output
- Prefer conventional block and table layouts for invoices, reports, and forms.
- Use print-oriented rules that the feature matrix lists as supported rather than relying on browser-only behavior.
- Replace JavaScript-driven layout with server-side HTML generation.
- Test every font, image, and page-break rule in the exact library version used in production.
A page that looks correct in Chrome can therefore differ in the PDF. Treat the feature matrix as the compatibility checklist for your actual selectors and properties, not as a guarantee that arbitrary web pages will render identically.
iText pdfHTML or OpenHTMLToPDF?
OpenHTMLToPDF is a credible pure-Java alternative. Its project describes a renderer for well-formed XML/XHTML and some HTML5 using CSS 2.1 and later, producing PDF or images. It also cautions that modern HTML5 should be specially crafted for its engine. Compare the engines against your template and deployment requirements:
| Decision axis | iText pdfHTML | OpenHTMLToPDF |
|---|---|---|
| Input model | Accepts an HTML String directly, with optional ConverterProperties. |
Pure-Java renderer centered on well-formed XML/XHTML and a reasonable subset of HTML5. |
| CSS/HTML coverage | Documented feature matrix; browser-only modules such as scripts, animations, transitions, and custom properties can be unsupported or partial. | CSS 2.1 and later within its supported subset; modern HTML5 may need special authoring. |
| Resource resolution | Set a base URI for relative stylesheets, images, and fonts. | Validate the equivalent resource-resolution configuration for the version you deploy. |
| Output engine | iText Core and pdfHTML. | PDFBox-based output engine. |
| Accessibility and PDF/A | Evaluate the capabilities and configuration required by your conformance target. | Evaluate the capabilities and configuration required by your conformance target. |
| License | AGPL for non-commercial use; commercial deployments require a commercial license. | Review the project’s license and your obligations for the chosen release. |
Choose based on the features your template actually uses, the PDF/A or accessibility requirements you must meet, dependency footprint, and licensing—not on how closely a browser preview resembles the source.
Troubleshoot missing styles and broken PDFs
The PDF has no styling
Cause: the CSS was never inserted into the HTML, the <style> tag was placed outside <head>, or the generated string is malformed. Fix: log the final HTML string, confirm the CSS appears between <style> and </style>, and validate the markup before conversion.
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Images, fonts, or linked files are missing
Cause: relative URLs have no usable origin. Fix: set ConverterProperties.setBaseUri to the containing directory, check the path spelling and process permissions, and test the resource from the same runtime environment as the converter.
A browser layout does not match the PDF
Cause: the template uses a CSS module or HTML behavior that pdfHTML supports only partially or not at all. Fix: consult the feature matrix, simplify the affected layout, and replace scripts, animations, transitions, custom properties, or unsupported modern layout rules with static, print-oriented markup.
Conversion fails while reading an asset
Cause: a referenced resource is unavailable, unreadable, or points to the wrong base directory. Fix: remove references one at a time to identify the failing asset, then correct the URI or package the asset with the application.
The application builds but cannot be released
Cause: dependency and license review was postponed. Fix: pin the approved html2pdf version, record transitive dependencies, and obtain the appropriate AGPL or commercial authorization before deployment.
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Reliability and performance considerations
- Generate the final HTML once and write directly to the destination stream; this avoids an unnecessary temporary PDF buffer.
- Keep templates and their asset directory together so the configured base URI is deterministic across development, CI, and production.
- Include representative long tables, page breaks, fonts, and images in automated PDF checks. A successful method call alone does not prove visual correctness.
- Expect asset loading to affect conversion time when resources are outside the process. Prefer locally packaged resources when repeatability matters.
- Capture conversion exceptions with the document identifier and resolved asset paths, but avoid logging sensitive invoice or customer data.
Practical checklist
- Assemble valid HTML with a single
<style>block containing the CSS string. - Call
HtmlConverter.convertToPdf(html, outputStream)for a self-contained document. - For relative resources, create
ConverterPropertiesand set a base URI to the correct template directory. - Check the pdfHTML feature matrix for every nontrivial CSS rule.
- Test the generated PDF for fonts, images, page breaks, accessibility, and required PDF/A conformance.
- Complete dependency and licensing review before shipping.
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Frequently Asked Questions
How can I verify that a relative URL uses the intended base directory?
Print the base URI at startup and inspect the final HTML for each relative reference. Then run the converter in the same working directory and under the same operating-system account used in production; a path that exists only on a developer workstation is not a valid deployment test.
Should the CSS be kept in a separate template file?
It can be, provided your application reads the template and stylesheet and assembles one final HTML string before conversion. The converter needs the resulting HTML string; keeping source files separate is an application-organization choice.
What is the safest way to handle a browser-only CSS feature?
Do not assume that a browser preview proves support. Check the pdfHTML feature matrix for the exact property or selector, create a small fixture demonstrating the desired result, and replace the rule with a static print-oriented equivalent if support is partial or absent.
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