XSLT正则表达式只接受字符串中的几个字符

Question

I am writing a regular expression which will allow only below special characters:

- _ * & . , #

I wrote below function which will avoid all the characters except mentioned in below pattern:

<xsl:function name="wd:allowed_characters">
    <xsl:param name="input_param" />
    <xsl:if test="$input_param !=' '" >
        <xsl:value-of select="normalize-space(replace($input_param,'[^.#, \- _ * a-zA-Z0-9]',''))" />
    </xsl:if>
</xsl:function>

My problem is whenever I try to add & in the pattern at any place, I got below errors:

Severity: fatal
Description: The entity name must immediately follow the '&' in the entity

Severity: error
Description: Failed to compile stylesheet. 1 error detected.

I want to know about how can I add & in the pattern like other special characters?

Answer 1

XSLT is written in XML, so the source code of your XSLT stylesheet must be well-formed (and generally also valid) XML. In XML there are five special characters: < , > , & , " , ' which roughly can only be used as follows:

• Inside attribute values, you must escape quotes if the quote is also the bounding character, as in test=" "foo" " . Often you can write an attribute value by surrounding it with the other quote: test=' "foo" ' or test=" 'foo' " are both valid. In XPath, which is typically written in XSLT inside an attribute value, this is a common way to write string literals (this is what you are already doing in your code above).
• Either in attribute values or any other place where free text is allowed, you must always escape < and & in < and & respectively.
• The > never needs to be escaped, but many people do.
• The five "escapes" are always available as named entity references, regardless of the presence of a DTD: < , > , & , " and ' , other named entity references first need to be declared in a DTD (as is often done for   ).
• Only inside a CDATA section (and in a comment) you do not need to escape any of these characters: <![CDATA[<hello>&]]> is exactly the same as <hello>& . CDATA sections are only allowed in text nodes, not in attribute values.

It is often confusing. If the source document contains < in the XML, you won't be able to find it by comparing it to a string < , because essentially it's just the < character. Instead you must search for < . However, since XSLT is written in XML, writing <xsl:if test="contains(., < )" will search for the < character, not the four-character string < .

In regard to your question, you can write your expression simply as follows:

• replace($input_param,'[^&.#,_*a-zA-Z0-9-]','')
• I've removed the spaces (not sure that was intentional)
• I've place the - at the end, where it does not require escaping
• Your xsl:if is redundant: the normalize-space will make a string consisting of only spaces the same as the empty string. With or without the xsl:if will have the same results

Note: because of the complexities of escaping, quote-issues and other things, it is common to write a regular expression in a variable's sequence constructor, to prevent those issues to happen in the first place (added the x-modifier to allow whitespace in the regex):

<xsl:variable name='regex' as='xs:string'>
    [^&amp;.#,_*a-zA-Z0-9-]
</xsl:variable>

<xsl:function name="wd:allowed_characters" as="xs:string">
    <xsl:param name="input_param" as="xs:string" />
    <xsl:value-of select="
       normalize-space(
       replace($input_param, $regex, '', 'x'))" />
</xsl:function>

Answer 2

According to my knowledge, in XML, we can't use direct key of '&', which should be combination of '&[A-z0-9]+;'. In XML we can use either '&amp;' or '&#x0026;' entity formats. In regex '[^.#, &amp;&#x0026;- _ * a-zA-Z0-9]' can be used.