[FIXED] How to validate a JSoup selection string

Issue

I am working on a program that gives the user the opportunity to define his own selection string. For example in the expression:

doc.select("a[href]");

The user would have specified the "a[href]" part. Now my question is, how can I check if the passed in string is a valid JSoup selector string? Does anyone know how to validate this?

Any help would be very much appreciated.

Thanks

Solution

approach 1: Edit the Jsoup source and make the Parser public or implement your own method there

approach 2: Parse a simple dummy element and catch the exceptions. if one is thrown: query is not valid, else it's ok. Not the best solution but it works.

Here's an example:

private static final Element dummy = new Element(Tag.valueOf("p"), ""); // used for "testparsing"

// ...

public static boolean isValid(String query)
{
    if( query == null ) // Check for null
        return false;

    try
    {
        Selector.select(query, dummy); // Use the querystring on the dummy - returnvalue is not relevant
    }
    catch( Selector.SelectorParseException | IllegalArgumentException ex ) // these exceptions are thrown if something is not ok
    {
        return false; // If something is not ok, the query is invalid
    }

    return true; // All ok, query is valid
}

Test:

System.out.println(isValid(null)); // not valid
System.out.println(isValid("div.abc")); // valid
System.out.println(isValid("p[")); // not valid
System.out.println(isValid("a:matchesxy")); // not valid
System.out.println(isValid("div > a")); // valid

Testresult:

false
true
false
false
true

Answered By - ollo
Answer Checked By - David Marino (JavaFixing Volunteer)