Apache FOP处理含特定关键词URL生成PDF失败求助

Let's break down why this error pops up and how to fix it quickly:

Why the Error Happens #

This is a classic XML syntax gotcha. XML treats the & character as the start of an entity reference (like & for an actual ampersand). When your URL includes &rel or &utm directly in the XML, the parser thinks you're trying to reference an entity named rel or utm—but those aren't valid built-in XML entities, and you haven't defined them. On top of that, it's missing the required ; at the end of the supposed entity reference, which triggers the exact error you're seeing.

Even if your URL looks like it has &rel=0 (like your example), double-check if that's actually what's being passed to FOP. Sometimes dynamic code or templating engines can un-escape & back to & before FOP parses the XML, bringing back the issue.

Step-by-Step Fixes #

• Escape every ampersand in URLs for XML: Every single & in your URL must be replaced with & when embedding it in XML. For your example URL, ensure it's written as:

  https://www.youtube.com/embed/1mDT-x2XnEg?autoplay=1&rel=0&feature=oembed&enablejsapi=1&wmode=opaque
  

  Don't skip any parameters—even one un-escaped & will break things.

• Use XML libraries to build content (don't hand-write XML): If you're generating the XML dynamically (e.g., in Java), never concatenate raw strings to build XML. Use a proper XML API like JDOM, DOM4J, or Java's built-in XML tools. These libraries automatically escape special characters like &, <, and " for you, eliminating manual mistakes.

• Validate your XML first: Before passing it to FOP, run your XML through a validator (like xmllint on the command line) to catch syntax issues early. This will point you straight to any un-escaped & characters hiding in your code.

• Watch for double-escaping issues: If you're using a templating system (like XSLT) to generate the FO file, make sure you're not accidentally un-escaping the URL. For example, misusing disable-output-escaping="yes" could turn & back into & and reintroduce the error.

Example of Valid XML Usage #

Here's how a properly formatted FO element with your URL should look:

<fo:external-graphic src="https://www.youtube.com/embed/1mDT-x2XnEg?autoplay=1&amp;rel=0&amp;feature=oembed&amp;enablejsapi=1&amp;wmode=opaque" />

内容的提问来源于stack exchange，提问作者Magnus Melwin