java.net.MalformedURLException: no protocol for entity in XML

Can you explain a bit more what you're trying to do? Are you using XSLT to transform the XML into another format?

Is it correct that your code includes those file_xx.xml documents into one big XML file? How does that work and does it mean the declaration is included as well? Is the resulting XML well formed?

Yes, I'm using XSLT (Saxon 8.7) to transform the XML to HTML format. Instead of one big XML file, my main XML contains only the external entity references to the smaller files (file_xx.xml). Main reason is the smaller files are created separately, so we only use external entity for those to keep thing simple.

Both of the main and smaller XML files are valid. When I put them together into one big file, it validates without any problem. In fact I can transformed it fine.

I can transform the main + external entity xml fine ** if ** I run it on local Windows desktop. The DTD is valid as well as a separate project.dtd file.

The problem only appears when it is using external entity, on the server. I have a java program that does the transform.

In my main xml, I can't use file:///file_xx.xml because I can't validate it properly using XML editor. In Windows it tries to find it in C:\file_xx.xml.  Nor can I use the full path to the file (file:///C:/myfolder/xslt/project_1/file_xx.xml. Because the path will not be valid after I put the file to the server. So relative path is the only way to go I believe. But this became a problem where the XSLT processor couldn't find the file_xx.xml because there is no protocol defined.

Using the external entity is the requirement so I can't put the content together as one big xml file.

O.S

You can use the document() function in XSLT to read multiple XML documents. This example assumes the file_xx.xml files are in the same folder as the xml and xslt. That is easiest to start with, but you can move them around like you do with HTML, using relative paths etc.

http://www.xml.com/pub/a/2002/03/06/xslt.html

<!-- index.xml -->
 
<?xml version="1.0" encoding="utf-8"?>
 
<document xmlns:xlink="http://www.w3.org/1999/xlink">
   <title>Title here</title>
   <files>
      <file>file_01.xml</file>
      <file>file_02.xml</file>
      <file>file_03.xml</file>
      <file>file_04.xml</file>
   </files>
</document>
 
<!-- file_01.xml -->
 
<?xml version="1.0" encoding="UTF-8"?>
<test>
	<id>345</id>
</test>
 
<!-- test.xsl -->
 
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
	<xsl:template match="files">
		<xsl:apply-templates select="file"/>
	</xsl:template>
	
	<xsl:template match="file">
		<xsl:apply-templates select="document(.)/path/to/node"/>
	</xsl:template>
</xsl:stylesheet>

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Thanks for the suggestion. Unfortunately the file format and the external entity references must remain unchanged. I'll try to implement your solution on my program but the files were created from a conversion process that I can't change. Part of the requirment is that I shouldn't change any of the source either. That's a bummer. Seems like I have no control over the file format. Therefore I need to find another way to deal with the external entity.