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Best way to validate non-printable ascii characters in XML

Application needs to validate the different input XML(s) messages for non-printable ascii characters. We currently know two options to do this.
Change the XSD to include the restriction.
Validate the input xml string in java application using Regular Expression
Which approach is better in terms of performance as our application has to return the response within a few seconds? Is there any other option available to do this?

It's mainly a matter of opinion but if you have an XSD that seems to be the natural place to include the validations. The only thing you may need to consider is that via XSD you will either fail or pass, whereas with ad-hoc java validation you can ignore non-printable, or replace or take an action without failing the input completely.

The only characters that are (a) ASCII, (b) non-printable, and (c) allowed in XML 1.0 documents are CR, NL, and TAB. I find it hard to see why excluding those three characters is especially important, but if you already have an XSD schema, then it makes sense to add the restriction there.
The usual approach is not to make these three characters invalid, but to treat them as equivalent to space characters, which you can do by using a data type that has the whitespace facet value "normalize" or "collapse".

In an XML document, is it possible to tell the difference between an entity-encoded character and one that is not?

I am being feed an XML document with metadata about online resources that I need to parse. Among the different metadata items are a collection of tags, which are comma-delimited. Here is an example:
<tags>Research skills, Searching, evaluating and referencing</tags>
The issue is that one of these "tags" contains a comma in it. The comma within the tag is encoded, but the commas intended to delimit tags are not. I am (currently) using the getText() method on org.dom4j.Node to read the text content of the <tags> element, which returns a String.
The problem is that I am not able -- as far as I'm aware -- to differentiate the encoded comma (from the ones that aren't encoded) in the String I receive.
Short of writing my own XML parser, is there another way to access the text content of this node in a more "raw" state? (viz. a state where the encoded comma is still encoded.)

When you use dom4j or DOM all the entities are already resolved, so you would need to go back to the parsing step to catch character references.
SAX is a more lowlevel interface and has support via its LexicalHandler interface to get notified when the parser encounters entity references, but it does not report character references. So it seems that you would really need to write an own parser, or patch an existing one.
But in the end it would be best if you can change the schema of your document:
<tags>
<tag>Research skills</tag>
<tag>Searching, evaluating and referencing</tag>
</tags>
In your current document character references are used to act as metadata. XML elements are a better way to express that.

Using LexEv from http://andrewjwelch.com/lexev/, putting xercesImpl.jar from Apache Xerces on the class path, I am able to compile and run some short sample using dom4j:
LexEv lexEv = new LexEv();
SAXReader reader = new SAXReader(lexEv);
Document doc = reader.read("input1.xml");
System.out.println(doc.getRootElement().asXML());
If the input1.xml has your sample XML snippet, then the output is
<tags xmlns:lexev="http://andrewjwelch.com/lexev">Research skills, Searching<lexev:char-ref name="#44">,</lexev:char-ref> evaluating and referencing</tags>
So that way you could get a representation of your input where a pure character and a character reference can be distinguished.

As far as I know, every XML processing frameworks (except vtd-xml) resolve entities during parsing....
you can only distinguish a character from its entity encoded counterpart using vtd-xml by using VTDNav's toRawString() method...

In Java, How to detect if a string is unicode escaped

I have a property file which may/ may not contain unicode escaped characters in the values of its keys. Please see the sample below. My job is to ensure that if a value in the property file contains a non-ascii character, then it should be unicode escaped. So, in the sample below, first entry is OK, all entries like the second entry should be removed and converted to like the first entry.
##sample.properties
escaped=cari\u00F1o
nonescaped=cariño
normal=darling
Essentially my question is how can I differentiate in Java between cari\u00F1o and cariño since as far as Java is concerned it treats them as identical.

Properties files in Java must be saved in the ISO-8859-1 character set for Java to read them properly. That means that it is possible to use special characters from Western European languages without escaping them. It is not possible to use characters from other languages such as those from Easter Europe, Russia, or China without escaping them.
As such there are only a few non-ascii characters that can appear in a properties file without being escaped.
To detect whether characters have been escaped or not, you will need to open the properties file directly, rather than through the Properties class. The Properties class does all the unescaping for you when you load a file through it. You should open them using the File class or though System.getResourceAsStream as an InputStream. Once you do so you can scan through the input stream one byte at a time and ensure that all bytes are in the 0x20-0x7E range plus new lines \r and \n which is the ASCII range of characters you would expect in a properties file.
I would suggest that your translators don't try to write properties files directly. They should provide you with documents like spreadsheets that you convert into properties file. Or they could use a translation editor such as Attesoro (which I wrote) to let them save the properties files properly escaped.

You could simply use the native2ascii tool, which performs exactly this conversion (it will convert all non-ASCII characters to escapes but leave existing escapes intact).

Your problem is that the Java Properties class decodes the properties files, assuming ISO-8859-1 encoding, and parsing escaped unicode characters.
So from a Properties point of view, these two strings are indeed the same.
I believe if you need to differentiate these two, you will need to write your own parser.
It's actually a feauture that you do not need to care by default. The one thing that strikes me as the most odd is that the (only) encoding is ISO-8859-1, probably for historical reasons.

The library ICU4J seems to be what you're looking for. See the Normalization page.

Escape sequences in XML

I'm getting an Exception due to special characters when Xml is accessed by client
Can any one help me...?

You need to set the correct encoding, and make sure the XML document is created with the same encoding.
<?xml version="1.0" encoding="INSERT ENCODING HERE"?>

You will need to ensure the special characters are enclosed within CDATA sections:
<![CDATA[
some special characters here
]]>

I have found my mistake in my case while opening/reading the XML i'm getting the error because of three symbols. So need to replace the Character: <>& by EntityName: <>&. Then only the parsing error will not be displayed.
Click Here to see HTML Symbol Entities Reference
Click Here to Read XML Basic Generation
In other scenario instead symbols the Entity names need to be replaced then only parsing exception will not be displayed.

You can include XML's special characters in XPL. XPL is structured exactly like XML but allows the special characters. The XPL to XML conversion utilities will take care of all the details for you. http://hll.nu

Escaping an xml string in java

I read elements with CDATA sections from a rss-feed which I need to convert to valid xml. The content in the CDATA section is mostly valid xhtml, but some times characters like ampersand appear in attributes (url's).
I can use .replaceAll("&", "&") to solve this but thinking a bit forward it may be that other invalid characters show up in attributes or text.
The CMS to which I'm importing the element, won't accept CDATA sections without setting up another configuration for the content, so my question is: is there any simple way to escape the string, only for attributes and text?
I'm using the jdom library to manipulate the xml after the import.
Edit: I've checked out apache's StringEscapeUtils, but this is escaping the whole string. I need something that will only escape attribute values and text inside elements.

Apache Commons provides handy functions for this: StringEscapeUtils

When you use JDOM it will automatically correctly escape ay content that needs it. Is your CMS loaded with the output of JDOM, or are you using some other library to populate the CMS...?
In essence, if you have valid XML input, and you use JDOM (something from org.jdom2.output.*) to output the data, then you will always have good output.... so, what are you doing to have broken output?
Rolf