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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsTo troubleshoot an HTML-to-PDF error in Java, first capture the exact exception and its full cause chain, then identify your renderer and version. Reduce the document to a minimal reproducer and check supported markup, resource access, fonts, and output-document state. These checks are more useful than a blanket try/catch or an automatic retry: most conversion failures have a specific input or configuration cause.
Start by preserving the actual failure
Record enough context to diagnose the problem without exposing private document contents. At minimum, capture:
- The exception class, message, and complete nested cause chain.
- The HTML-to-PDF library and dependency version, plus the Java runtime version.
- A document or job identifier and the stage that failed: parsing, rendering, writing, or closing.
- A minimal, sanitized HTML input that reproduces the issue, if one can be retained safely.
Do not replace the original exception with a generic error that discards its cause. Avoid logging full documents if they may contain personal, confidential, or otherwise sensitive data; keep a sanitized reproducer in an appropriately protected location instead.
Identify the renderer before interpreting the exception
There is no single Java HTML-to-PDF exception taxonomy. Error classes and messages depend on the renderer. In iText pdfHTML, Html2PdfException is documented as a runtime exception for conversion failures. Its API lists cases involving a font provider with zero fonts, a PDF document that is not in writing mode, and unsupported encoding. Read the exact message and address the matching cause rather than treating every instance as the same problem. iText pdfHTML 6.3.2 API: Html2PdfException
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Separate conversion failures from output failures
Determine whether the exception occurs while the renderer parses or lays out the HTML, or later while the application writes or closes the destination. A rendering error points toward markup, fonts, or resources; an output-stage error may instead involve a missing directory, inadequate permissions, an unwritable destination, or a stream closed too early.
Reduce the input and check renderer support
Validate or normalize generated HTML, then remove unrelated content until the smallest failing document remains. Check the exact features it relies on—such as markup, CSS, SVG, scripts, and layout behavior—against the renderer’s documented support. A Java PDF renderer is not automatically a full web browser.
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For example, OpenHTMLtoPDF describes support for a reasonable subset of well-formed XML/XHTML and some HTML5 using CSS 2.1 and later standards. That is not a guarantee of complete modern-browser behavior. If the reduced example depends on unsupported content, change the input or select a renderer whose documented feature set fits the requirement; exception handling alone will not make the feature work. OpenHTMLtoPDF project documentation
Resolve relative resources from the right base
Relative references need a base location. If the HTML includes a path such as images/logo.png, configure the source document’s location as the base URI so the renderer can resolve that path. The iText tutorial demonstrates setting a BASEURI for nearby resources in conversion examples. iText: Chapter 1, Hello HTML to PDF
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Then verify that the process doing the conversion—not just your development browser—can read each referenced stylesheet, image, and font. Check filesystem permissions and network access. Do not assume the renderer inherits a browser’s cookies or authenticated session; for protected or generated assets, configure a suitable resource retrieval or resolution mechanism.
Make font selection predictable
When using a custom font provider, confirm it contains at least one usable font and register the font files the document needs. Test in the same runtime or container used in production. The iText font guide describes the default provider’s standard and built-in fonts and glyph fallback, and notes that indiscriminately registering system font directories can make font selection vary across machines. It also warns that font embedding restrictions can trigger exceptions. iText: Chapter 6, Using fonts in pdfHTML
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A conversion that completes is not necessarily visually correct: missing glyphs or substituted fonts can alter the result without a thrown exception. Compare the output from the production environment with the expected document, especially when font availability differs between machines.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check PDF document state and the destination
- Make sure the destination directory exists and the conversion process can write to it.
- Keep an output stream open until conversion has finished; check that another part of the application has not closed it prematurely.
- If you supply a PDF document to the conversion path, confirm it is configured for writing when that path requires writing. iText’s API explicitly includes a not-in-writing-mode error.
- After conversion, verify that the output is non-empty and can be opened as a PDF before returning or serving it.
These checks distinguish a successful render from a failure or an unusable artifact. Do not return an empty or partial file as though conversion succeeded.
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Handle errors at the application boundary
Catch a library-specific exception where your code can take an action specific to that failure. Otherwise, catch an appropriate broader exception at the job boundary, preserve the original cause, attach safe job context, and return a structured failure to the caller. Avoid reporting a successful conversion when the renderer produced no valid PDF.
Retry only when the cause may be transient, such as a temporary failure retrieving an external resource, and use a bounded retry policy. A retry is not a fix for malformed HTML, an unavailable font, an unsupported feature, or a stable document-state configuration error.
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Frequently Asked Questions
What should I include in a bug report for a Java HTML-to-PDF failure?
Include the renderer and dependency versions, Java runtime version, full exception and cause chain, the failing stage, and a minimal sanitized reproducer. Exclude sensitive document contents.
Does catching Html2PdfException make an unsupported CSS feature work?
No. Handling reports the failure; it does not add renderer support. Confirm the required HTML and CSS features are supported, then change the document or use a renderer with a suitable documented feature set.
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