Is there a Java utility to verify if a string is a valid HTML escape character?

Question

I want a method in the following format:

public boolean isValidHtmlEscapeCode(String string);

Usage would be:

isValidHtmlEscapeCode("A") == false
isValidHtmlEscapeCode("&#1513;") == true // Valid unicode character
isValidHtmlEscapeCode("&#x5E9;") == true // same as 1513 but in HEX
isValidHtmlEscapeCode("&#78975332;") == false // Invalid unicode character

I wasn't able to find anything that does that - is there any utility that does that? If not, is there any smart way to do it?

I don't mind a function that deals with those - but it is not my requirement (in other words - I'm impartial regarding it) — RonK
– RonK, Commented Dec 20, 2012 at 15:25
Why can't you just check if it starts with &, ends with ; and middle portion consist of (i) a-z, 0-9 (ii) # followed by digits (iii) #x followed by hex digits? — Salman Arshad
– Salman Arshad, Commented Dec 20, 2012 at 15:43
@SalmanA I was hoping for a smarter way to do it - I don't like reinventing wheels — RonK
– RonK, Commented Dec 20, 2012 at 15:49

Esailija · Accepted Answer · 2012-12-20 15:53:58Z

3

public static boolean isValidHtmlEscapeCode(String string) {
    if (string == null) {
        return false;
    }
    Pattern p = Pattern
            .compile("&(?:#x([0-9a-fA-F]+)|#([0-9]+)|([0-9A-Za-z]+));");
    Matcher m = p.matcher(string);

    if (m.find()) {
        int codePoint = -1;
        String entity = null;
        try {
            if ((entity = m.group(1)) != null) {
                if (entity.length() > 6) {
                    return false;
                }
                codePoint = Integer.parseInt(entity, 16);
            } else if ((entity = m.group(2)) != null) {
                if (entity.length() > 7) {
                    return false;
                }
                codePoint = Integer.parseInt(entity, 10);
            } else if ((entity = m.group(3)) != null) {
                return namedEntities.contains(entity);
            }
            return 0x00 <= codePoint && codePoint < 0xd800
                    || 0xdfff < codePoint && codePoint <= 0x10FFFF;
        } catch (NumberFormatException e) {
            return false;
        }
    } else {
        return false;
    }
}

Here's the set of named entities http://pastebin.com/XzzMYDjF

edited Dec 20, 2012 at 15:53

answered Dec 20, 2012 at 15:38

Esailija

140k24 gold badges280 silver badges328 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

RonK Over a year ago

Thanks, this was the best solution for my issue - I slightly modified it by adding a ^ at the beginning of the pattern and a $ at the end so for strings like hello { world it will not return true

Esailija Over a year ago

@RonK cheers, yeah I use this regex for extracting html entities and forgot to modify it ^^

NoobCoder Over a year ago

named entities paste bin needs updating..could you update please

Korgen · Accepted Answer · 2012-12-20 15:25:59Z

2

you might want to have a look at Apache commons StringUtils: http://commons.apache.org/lang/api-2.3/org/apache/commons/lang/StringEscapeUtils.html#unescapeHtml(java.lang.String)

with the unescapeHtml you could do sth. like:

String input = "A";
String unescaped = StringEscapeUtils.unescapeHtml(input);
boolean containsValidEscape = !input.equals(a);

answered Dec 20, 2012 at 15:25

Korgen

5,4191 gold badge32 silver badges46 bronze badges

Comments

hoaz · Accepted Answer · 2012-12-20 15:36:54Z

2

Not sure if this is a perfect solution, but you can use Apache Commons Lang:

try {
    return StringEscapeUtils.unescapeHtml4(code).length() < code.length();
} catch (IllegalArgumentException e) {
    return false;
}

edited Dec 20, 2012 at 15:36

answered Dec 20, 2012 at 15:24

hoaz

10.2k4 gold badges48 silver badges55 bronze badges

3 Comments

RonK Over a year ago

StringEscapeUtils doesn't handle anything in the &#xxx; format. So basing my code on it will not work

hoaz Over a year ago

It does indeed, unescapeHtml4 contains NumericEntityUnescaper, so it should handle them

hoaz Over a year ago

looks like it throws IllegalArgumentException when you pass invalid entity, so I've updated my solution a bit

Aioros · Accepted Answer · 2012-12-20 15:35:53Z

1

This should be the method you wanted:

public static boolean isValidHtmlEscapeCode(String string) {
String temp = "";
try {
    temp = StringEscapeUtils.unescapeHtml3(string);
} catch (IllegalArgumentException e) {
    return false;
}
return !string.equals(temp);
}

answered Dec 20, 2012 at 15:35

Aioros

4,3931 gold badge20 silver badges22 bronze badges

Comments

Brent Worden · Accepted Answer · 2012-12-20 15:51:06Z

0

Try matching using a regular expression:

public boolean isValidHtmlEscapeCode(String string) {
    return string.matches("&;#([0-9]{1,4}|x[0-9a-fA-F]{1,4});");
}

Or to save some processing cycles you can reuse the regex for multiple comparisons:

Pattern pattern = Pattern.compile("&;#([0-9]{1,4}|x[0-9a-fA-F]{1,4});");

public boolean isValidHtmlEscapeCode(String string) {
    return pattern.matches(string);
}

The source of the regex can be found at RexLib.com

edited Dec 20, 2012 at 15:51

answered Dec 20, 2012 at 15:30

Brent Worden

11k8 gold badges57 silver badges59 bronze badges

5 Comments

RonK Over a year ago

Not bad - but isValidHtmlEscapeCode("𘚟") will return true

Brent Worden Over a year ago

@RonK the regex has been changed to correct the length constraint.

Esailija Over a year ago

@RonK 𘚟 is valid... in decimal, up to 􏿿 is valid.

RonK Over a year ago

@Esailija - thanks, so length validation is not enough - the value of the number also needs to be validated.

Esailija Over a year ago

@RonK among other things, such as character references that would amount to lone surrogates, which I don't think htmlUnescape accounts for. Even chrome and firefox inconsistently treat &#xd801; as a valid entity, transforming it to �

Collectives™ on Stack Overflow

Is there a Java utility to verify if a string is a valid HTML escape character?

5 Answers 5

3 Comments

Comments

3 Comments

Comments

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

3 Comments

Comments

3 Comments

Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related