XSL template for converting XML to JSON

Question

I used saxon v9 to profile an XSL transformation which converts XML to JSON. The profiler tells me that the function which escapes certain characters takes about 70% of the total processing time. The conversion is important because otherwise the created JSON file will be invalid because of characters that break the strings.

java -jar saxon9he.jar -xsl:jsontransform.xslt -s:input.xml -o:output.json -TP

The "method" used to escape the values looks like this:

<xsl:template name="escapejson">
 <xsl:param name="string"/>
 <xsl:sequence select="replace(
 replace(
 replace(
 replace(
 replace( 
 replace(
 replace(
 replace(
 replace($string, '\\','\\\\'), 
 '/', '\\/'),
 '&quot;', '\\&quot;'),
 '&#xA;','\\n'),
 '&#xD;','\\r'), 
 '&#x9;','\\t'), 
 '\n','\\n'),
 '\r','\\r'),
 '\t','\\t')"/>
 </xsl:template>

Unfortunately, my XSL knowledge is too limited to create an optimum solution on my own. I assume the repeated call of replace is quite inefficient but don't know how to do it better.

Answer 1

I can believe it when the replace is the problem... it's creating a mess of nested code that's creating a lot of intermediate string values.

There's not much I can see to improve, though. The nesting can be reduced by combining a few of replaces...:

replace(.... , '\n|&#xA', '\\n')

Doing the same for \t and \r will reduce six calls to just three.

Additionally, I would consider wrapping the entire replace function in a matches call, that matches any of the patterns you are searching for, so you only need to do the full replacement call stack on values that actually require it. A large matches for all replaced values will, depending on how often values are actually required to be replaced, save time.

• Marged: Thanks a lot, I will try this when I have to access to my computer again. Do you think I could rewrite this into even less replace calls when using something similar to the declaration of this method: xsltfunctions.com/xsl/functx_escape-for-regex.html
• rolfl: I have worked with Micahael Kay in the past on JDOM/Saxon integration, and he's very friendly, knowledgable and active on Stack Overflow too. I would recommend you rephrase your question in terms of a "this code is my attempt at replacing search items in the document as part of the transformation and it sucks! What alternatives are there that I should consider?", and tag it with the saxon tag. I am pretty certain that he reads all saxon questions (and JDOM questions too).
• Marged: I tried your first suggestion and converted the 6 replaces into 3 which make use of the regex. The strange / sad thing is that when comparing 10 transformations of the original and the modified xslt the times are worse or equal.
• rolfl: @Marged - can we chat in The 2nd monitor
• Marged: As suggested by you I created a new question on SO stackoverflow.com/questions/31549633/…