检测字符串是否包含特定字符的最快方法

Question

I'm building an XML parser that goes over a big XML file and I'm looking for the fastest way to detect if a string contains a char(that isn't a " " , "\\n" or "\\r" ). I've tried using regex but it is too slow and heavy. Another method I tried was to get the ASCII number of " " , "\\n" and "\\r" and to reduce it from the size of the String, if it's larger then there's at least one char. This operation is also heavy. Good advice would be appreciated.

Edit - Clarification:

Too slow is 300 milliseconds for a line of XML parsing + string manipulation.

Examples to the 2 ways I implemented:

By Redex:

if (!str.matches(".*\\w.*")
{
  // str that doesn't contains chars
}

By summing up ASCII values:

if (numOfWhitespaces + numOfSpecialChars >= str.length()) // +1 for ending /r in
  str
{
    // str that doesn't contains chars
}

The first solution(Regex) is slower in 200 milliseconds. On a file with 500+ lines (where each line is being processed independently) it's crucial.

I hope it's clear enough. thanks!

Answer 1

The fastest way to scan a String is with a SAX listener

public void characters(char ch[], int start, int length) throws SAXException {
    for(int i=start, end = start+ length; i < end; i++) {
       if(ch[i] <= ' ') {
          // check if it is a white space
       }
    }
}

If you are not use a SAX parse or an event driven parser, this could be your performance bottleneck.

Answer 2

too slow is 300 milliseconds for a line of xml parsing + the string manipulation. The String " " detector doen't connect with the XML parser so don't confuse it together. The origin of the String doesn't matter at all for this topic.

The solution is:

By redex:

if (!str.matches(".*\\w.*")_
{
  // str that doesn't contains chars
}

By String methods:

if (numOfWhitespaces + numOfSpecialChars >= str.length()) // +1 for ending /r in
  str
{
    // str that doesn't contains chars
}

those lines should be applied on any String( it doesn't matter what is the string's origin). The time of the first solution(regex solution) is slower in 200 milliseconds after running two parallel runs, one with each solution, on a file with 50 lines (where each line contains a string that need to be checked)

I hope it's clear enough. thanks!